Vehicle Dynamics starting points and design process [Archive]

ChristianChalliner

10-24-2014, 08:07 AM

Hi everyone,

A little introduction about me and my team first, I am currently a third year Mechanical Engineering student at Aston University and a member of the Formula Student team. I certainly don't know everything but I'm willing to learn even if it might be a painful process at times, similarly, I am not a maths genius, I am competent with most maths but I'm sure there will be times where I will be asking things which seem trivial to most of you! The team structure consists of 16 members and is built around the idea of FSAE/FS being a year project for third years (of which there are 9), as such the 'main' areas (if you like) are split between the 9 third year students and have been defined as:

1. Transmission and Engine
2. Uprights and Brakes
3. Suspension
4. Pedal Box
5. Bodywork
6. Chassis
7. Driver Environment
8. Intake/Exhaust
9. Suspension Arms

Whilst you may not agree with the splits and grouping of the items that is unfortunately how it is and has been defined/fixed by the project supervisor.

My area is 'Suspension' however, I'd prefer to call it general Vehicle Dynamics since I have control of all the inboard and outboard attachment points within reason.

So what is the purpose of this thread?

The reason I've created this thread is not to get everyone to answer my questions for me, that's not what I want to do and I don't learn anything from someone telling me "you want xx amount of camber compensation in roll because we did it last year and it worked pretty well". I don't wish to be spoon fed what to do but in some instances I've found myself hunting around in the dark with no proper direction and it's these times where I think "well I could really do with someone who has experience looking over what I've done and putting me back on the right track or finding my errors". What I'm trying to say is that I would like opinions on my train of thought, direction, method (analysis) and how it could be improved to ensure that I haven't overlooked something critical.

As such, what follows is my basic interpretation of how I see the problem I've been given and the solution path I believe I should be going down.

My thoughts

In the simplest form my job is to design a system which maximises the tyre performance and hence car performance in order to extract the best possible laptime and in turn gain us the most points possible in the dynamic events. As the tyres are the only part of the car in contact with the ground then it seems clear that building a system around what the tyre 'likes' is the way it should be done, similarly, it is important that the car be responsive to the driver inputs (whilst have predictable handling characteristics) so that the driver has confidence in the car and is not frightened to drive it at its limit.

Thus, it appears the system should be designed 'outside in' in the sense of design driven from the tyre, not by building a chassis and then bolting suspension to it. To me it appears that the next step is to study the tyre.

What do I already know?

I accept that I actually know very little and that this will be a long journey in furthering my understanding of these systems but as a starting point I have a copy of RCVD of which I have read both sections in regards to tyres and tyre data (I understand that these are only introductions and are not the full story) hence I know the definitions of the basic parameters: slip angle, tyre aligning torque, scrub radius, KPI, pneumatic and mechanical trail, tyre load sensitivity, cornering stiffness, slip ratio, camber, basic pressure effects, etc.

I have some experience of the competition having helped out last years team at the FSUK competition and I've looked over various threads on here for the past few years and picked up a few things, likewise I have read the Pat's Corner articles on FSG.

I know that bump and roll steer are to be avoided and can be done so by pointing the tie rods to the instant centers.

I know that I know not nearly enough :p

What is fixed?

Wheels -13x6 w/ 0.5inch positive offset
Tyres - 6.2/20-13 Avon A92 compound

What do I have available to work with/from?

RCVD
OptimumG folder
Avon tyre data - http://www.avonmotorsport.com/resource-centre/downloads
Optimum K,T&D (Subject to purchase by supervisor)
Excel
Pen + paper
Last years (broken) car

What have I done so far?

In order to determine a rough wheelbase and track widths I used the information available from Racecar Engineering along with the times for Skidpan, Acceleration and Autocross at FSUK last year to produce graphs and lines of best fit in excel, whilst the data had considerable variance due to the variety of powertrains used and design philosophy (wings or not, etc) the suggested outcome was that the minimum allowable wheelbase (1525mm) and a track width only sufficient for the car to not roll at its max lateral acceleration event was sufficient. I also noticed that most cars appear to run narrower rear tracks than fronts but plotting the track ratios against times for autocross suggested that this actually wasn't optimum and that a equal front and rear track was optimum. What I'd like to note about this last point is that I fully understand that the data for this comparison may be unreliable and that these initial conclusions may be proven incorrect at a later date.

I have also looked into the Avon Tyre data and the testing method. It appears to me that the idea of running the tyre on the outside of a drum is not really a fair comparison to running a tyre on a flat surface as it would do actually, surely the length of the contact patch is affected by the fact the road surface isn't actually flat and this in turn will affect the aligning torque readings? I'm certain that there are more discrepancies between this testing method and a flat road including the actual surface differences. Whilst I will look further into this I'd like to move onto my next point, As it is my desire to design the car around the tyre it seems that creating a tyre model should be the first step before deciding on anything else.

I understand that the idea is to normalise the loadings in order to 'fit' the data to a curve, the difficulty I am having is that whilst Avon provide co-efficients for a Pacejka '96 model I'd like to understand where these co-efficients actually come from, the actual 'fitting process' and how it works, if anyone could point me in the right direction (or work through it with me) on this I'd be very grateful. My intention is to add progress to this thread as I go along, as such there's not much here currently but if the thread lasts the lifespan of the project it should be decently comprehensive by the end!

Thanks,

Christian

Ahmad Rezq

10-24-2014, 09:08 AM

ChristianChalliner,

Designing the whole car depends on your understanding the competition and setting your targets. Setting your targets will help you to define ( Optimum Suspension Design ).
What is the response you are expecting your car to do ?
with the help of your tire data and your understanding of dynamics you can set initial suspension sketch and expect how this suspension will act when you simulate it. and again edit your design and repeat the process until you find your optimum.
it's a good idea to analysis other teams data like static weight dist wheel base track width etc . but try to think about them what are the effects of these things on your target performance? So again it depends on your targets set them and try to reach them, finish your car early and test it for more than couple of months

ChristianChalliner

10-24-2014, 06:43 PM

Thanks Ahmad I appreciate your input and it's given me something to think about (whilst jogging my memory on a few points),

The main issue of last years car was a general lack of response to driver inputs, having looked over the car since we have found considerable rear toe compliance due to: slop in rose joints; uprights of poor stiffness; unnecessarily small steer arms (<50mm); undersized bearings; poor chassis load path for the tie rod and a massive scrub radius (100mm+) all quite visible from applying very little force to the wheel. We also found considerable bump steer at the front along with: very short steer arms (55mm); limited steering angle due to the linkage inverting because of poor layout; heavy steering and again a large scrub radius (60mm).

A crude analysis of the forces acting about the steer axis at both ends of the cars shows that the tyre has considerably larger advantage over the tie rods than the tie rods do the wheel (Assuming that the mechanical trail is all the advantage the tyre has (I am fully aware that the pneumatic trail will be added to this and as such the tyre has even more advantage)). Thus I am not surprised that the car was unresponsive to driver inputs.

My initial aims are to solve these problems before going further in optimising the camber gain curves to suit the tyre, decide on roll center height and it's affects on how the weight is transferred (through the arms and the springs), decide on a rocker design (to give linear or rising rate springing) and then investigate anti-dive and anti-squat properties.

With regards to looking at others, as I see it a shorter wheelbase gives a lower moment of inertia so under acceleration there should be more weight transfer to the rear, more force on the tyre = more traction thus short wheelbase cars should perform well in acceleration. This also works both ways though and a shorter car will snap faster than a longer one making it susceptible to rapid handling changes (that the driver may struggle to deal with) however, for the slaloms the ability to change direction quickly must surely be a good thing. On a similar note a narrower track will mean your effective 'corner radii' for the slaloms will be larger so you will be able to pass through the gets utilising less steering angle and at a higher speed before the tyre lets go at the expense of the car being less stable (possibly a problem in braking zones?). I will throw out there that having a narrower track at the rear will move the balance towards oversteer and should also reduce the chance of your rear wheels clipping a gate but that is pure speculation on my part and I don't have the simulations to prove it.

I perhaps have failed to make my initial issues clear, the one which is causing me the biggest issue is that I don't fully understand the tyre data and what it means, for example: the Avon curves show data for various camber angles but I cannot make the connection as to how that will allow me to decide on what a suitable FVSAL length is and if the FVSAL length should shorten in compression or not, the only thing I see is that excessive camber gain with travel will mean that the contact patch is compromised severely in bump reducing the cars tractive and braking abilities but may be beneficial in roll as the camber angles will remain closer to the perceived 'ideal'.

All I am seeing is these lines on a page with the fairly obvious that as Fz increases Fx does and that the tyres peak at a given slip angle before the Fx value begins to drop off, likewise, the Fx values go up as camber is increased but does that mean I should endeavour to run with as much camber angle as possible without incurring extreme inside tyre temperatures and wear problems? I'm not sure it does. I feel like I'm really missing something vital to connect the dots here but I keep trying to read everything I can find on the subject but my understanding is not progressing :(

Our plan is to have the car ready at least two months prior to the competition so we can carry out significant testing to validate the design, optimise the setup and get the drivers comfortable in the car. The problem is I cant afford to wait until then to find out that I've missed something vital.

Claude Rouelle

10-24-2014, 09:14 PM

Christian,

1. At least you are stating your assets, your goals and even your doubts in a objective way. That is impressive.

2. Bump steer and roll steer is not necessarily a bad thing unless your tracks are very bumpy which is not really the case in FSAE/ FS. In any case, even without any pure kinematics bump or roll steer, you will have bump and roll steer by compliance to a point that most FSAE/FS teams have no idea of, do not calculate, or measure or integrate in their simulations and their car setup.

3. Yes it is about maximizing tire performance and car drive-ability. But its not only about maximizing each and all tires performances (that is grip) it is about also about balance (that means having the exact amount of yaw moment when you want / need it) and it is about control and stability. "THE" BEST Method to understand grip, balance, stability and control and tune your car using a decently relevant tire model understanding is to create your own Yaw Moment Vs Lateral Acceleration with Stability and Control simulation tool which is well described in RCVD and in our OptimumG seminars. It will help you to evaluate each car design and tuning parameter influence on those 4 criteria. That is THE method that makes our customers winning races and championship.

4. In your tools you should add OptimumLap. It is free of charge and it will help you to decide the priority on performance of weight, grip, aero and power. Yes it is "only" a mass point (that is also why it is free of charge) but we used it on a LMP2 (on pole) on the Le Mans circuit and our prediction was wrong by just 0.6 " on a 3'36" lap time.

In OptimumLap try different tire traction ellipse shapes and you will see which of lateral or longitudinal grip influences the most the lap time. When you will switch to your 4 wheel model that will be a good beginner to decide if you want to control more your camber variation in heave and pitch (braking and acceleration) or in roll (corner)

5. I have serious doubt about the relevance and the usefulness of the Avon tire data for FS: look at the graphs: you can't even see the peak slip angle for Fy..... You may want to consider using TTC data (if you do do not forget the Calspan sticker on your car)

6. Be careful about the track width size just to avoid tipping over under lateral acceleration; that doesn't take any transient effect, tire Mx, delta altitude between non suspended mass CG and instant center etc...

7. Equal front and rear track COULD be optimum ( I like that word :) ) except that when car do not have enough yaw angle (that means cars not driven at the limit which is the case of 90 % of FSAE 90% of the time) the driver most often will hit the cones with the inside rear wheel

8. I do not think the smallest wheelbase and smallest inertia in a FS/FSAE will make the car "too" snappy and un-drive-able; loot at competitive go-karts in tight corner; less inertia and still control-able.

Here is my advice for car design

1. Start by a simple mass point simulation
2. Then a steady state 2 wheel model
3. Then a steady state 4 wheel model with linear kinematics; roll and pitch centers do not move, spring and ARB stiffness and their motion ratio are constant, ratio camber variation per degree of roll or mm of heave constant
4. Non linear kinematics 4 wheel model, no compliance yet, still steady state but now you input your tire model to use the Yaw Moment Vs lateral acceleration simulation

At that time and only at that time you go to CAD. Not before.

There will be another OptimumG seminar in the UK around the Autosport show early January (dates to be decided soon) you might want considering it

10-24-2014, 10:56 PM

Our plan is to have the car ready at least two months prior to the competition so we can carry out significant testing to validate the design, optimise the setup and get the drivers comfortable in the car.

Christian,

I can see that although you have the right intentions, you are already HEADING WAY OFF COURSE. Sorry to be blunt, but because you are clearly putting a lot of thought into these posts I do want to help you.

First little tip, if you "plan to have the car ready two months prior to comp", then you more likely will still be bolting it together two hours before Scrutineering closes.

New plan - SIMPLIFY EVERYTHING, and get the car ready much, much earlier.
~~~o0o~~~

But biggest-picture stuff now.

Is your Team's Overall Goal to:
1. WIN OUTRIGHT!!! (or at least within the next few years)?
2. Learn to play video games?
3. Tread water, then enjoy the trip to the circus at the end of the year?

If 2 or 3, then I cannot help you.

If 1, then please read on. (BTW, well done Ahmad for also recognising the importance of setting clear targets.)

VERY IMPORTANT. This competition is there for the taking. By anyone. Your Team can win it!
* It DOES NOT require huge resources. Simple and cheap cars win regularly.
* It does not require huge experience. The Rules limit all of you to "students".

What IS required, and ALL THAT IS REQUIRED, is the WILL TO WIN.
~~~o0o~~~

Still big-picture stuff, but a bit more focussed.

By now I hope you have read Geoff's (Big Bird's) "Reasoning..." thread, stickied at top of thread list. Print it out and get all the Team members to read it. Several times, so as not to miss anything.

I also suggest the "Any way to objectively choose engine?" thread, and for your own area, the "Suspension Design" thread. (And, if you have time, any of the other threads that I have successfully hijacked. :))

The important point here is that at this stage you are FOCUSSING TOO MUCH ON LITTLE DETAILS, yet you have given us NO IDEA OF THE OVERALL CAR CONCEPT!

* Will your car be a low-power, non-aero, "super-light and agile", Tokyo Denki style car? (See also the quite neat Chinese Xiamen (splng?) car at a recent comp.)

* Or will it be a mega-horsepower, super-wide-tyred, Stuttgart-Panzer-tank style car?

* Or will it be a "brown go-kart with aero-undertray" Z-car?

It is important that your whole Team gets answers to these big questions early on, and STICKS WITH THEM. Your current Team structure probably works against this. (Frankly, I think it is a recipe for chaos.) However, you seem to be responsible for many of these big issues, so I hope you can get the rest of the Team to, err..., "sing from the same song sheet".
~~~o0o~~~

Focussing down on one particular medium-level issue.

As an example of what I was shouting about above, I strongly suggest that you DO NOT WASTE TIME on sophisticated tyre models. You already seem to have a pretty good grasp of the most important tyre issues.

Importantly, you have already found out that COMPLIANCE ISSUES, stemming from sloppy detail design, make any "tyre curves" that you come up with theoretically, utterly worthless in practice.

To repeat my mantra, at this stage your Team's goal is to build a four-wheeled-chair that can propel itself and the driver at an average speed of 50+ kph, over a distance of 30 km, WITHOUT FALLING APART. My good friends the toothless-hillbillies (lovely people) can do this easily with four wheelbarrow wheels and tyres, and absolutely no knowledge of "tyre curves", whatsoever.

To restress this yet again.
"... my job is to design a system which maximises the tyre performance and hence car performance..." <- WRONG!!!!!!!!!

Your job, and the rest of the Team's, is simply TO WIN!

A simple, reliable, "brown go-kart with a GOOD aero-undertray" could do this using only 80% of the maximum available tyre performance. Maybe with only 70 %, or less...

Anyway, tyres are consumables. They are easily changed and easily adjusted. The "static settings" of tyre brand, size, compound, rim-width, inflation-pressure, toe, and camber angles will get you 98% of the way to "maximum performance". Note that none of these depend on the suspension or any other part of the car (except, of course, for those compliance issues!).

On your billiard-table smooth FS tracks, things like suspension kinematics and springs & dampers make very little difference to the BIG-picture.
~~~o0o~~~

Probably too much for you to think about above, but a few more quick comments on your posts so far.

* Sell your 13" wheels and tyres. In case you already have a sponsorship agreement in place, Avon make good 10" tyres...

* DO NOT aim for the minimum "theoretical" track width. Your Team's inexperience may cost you dearly (ie. rollover!). Add at least ~10cm.

* DO NOT use "push/pullrods&rockers". These are a complete wank, and will just slow you down. Plain old "direct acting" SDs are enough.

* "I will throw out there that having a narrower track at the rear will move the balance towards oversteer..." NOPE! Think about it, but more importantly, DO NOT confuse yourself with such subtle details. KISS, and keep F&R tracks about the same.

* "I cannot ... decide on what a suitable FVSA length is ..." There is quite a bit on this on the Suspension Design thread (admittedly, it is only the rantings of some stupid old farts...). Also a very simple suspension with good FVSALs is shown at the top of page 25 (I think on this new forum).

* And many, many other details, which can be covered later.

Anyway, please keep "blogging the build". At the very least, your next year's Team should benefit from it...

And, like Jonny from Tasmania's thread, I really enjoy watching these things develop. Thanks! :)

Z

(PS. Just saw that Claude posted while I was writing this. No time now, but may comment more later...)

ChristianChalliner

10-25-2014, 06:16 PM

Thank you both for your thoughts, both of you have made me think deeper about certain issues and refocused me on the big picture, I'll answer both in order so firstly:

------------------------------------------

Claude, Thank you for the compliment :)

With regards to bump and roll steer not necessarily being problems I can see the value in having designed and controlled suspension driven steer characteristics however, I don't believe I am at the stage where I could currently implement a system that would improve the cars performance so for now I have decided I will focus on minimising the situation until my understanding of the system as a whole is better. Similarly, I was pondering the thought that all systems will have compliance to some extent so maybe analysing and 'tuning' the compliance may be more beneficial to car performance than just saying "well if I make it as stiff as possible it will be negligible" because in reality I'm pretty sure that the compliance can't/wont be negligible.

Your next point I think is where my understanding is most lacking, through past experience I have found that cars with better balance are both more fun to drive and turn better laptimes than ones with super sticky tyres and a poor balance so I can see the difference balance makes but I have a hard time quantifying the result. I'm away from my books currently but on Monday I will go through the OptimumG folder and start putting together a Yaw Moment Vs Lateral Acceleration calculator, I'll come back with the calculations and post them here once I've gotten somewhere for you all to see/comment on/etc.

I have looked into OptimumLap before and I did do some very basic experiments before the start of the year but they were mostly limited to mass vs laptime simulations, what I did find is that before I inputted some dummy values for load sensitivity the simulation was suggesting heavier cars were faster :p It did not occur to me to alter the effective friction ellipses in order to simulate setups favouring roll moments or bump and pitch moments but that does make sense to me in my head so I will revisit the program and perform those tests. I have a feeling that I will find lateral grip to be much more important though due to the nature of FSAE tracks.

Your comments on the Avon tyre data has somewhat validated my thoughts that I was potentially wasting my time trying to make something from it. I was pushing for the faculty advisor to purchase the TTC data over summer but I did not get very far, I will cover the reasons why at the end of this post in the 'big picture' summary I will do.

Regarding track widths, you have raised good points to suggest I was somewhat too keen to come to an early conclusion so I think I'll take a step back and look into it again once I've created a simple calculation model, it makes sense to me that a transient loading would (and indeed does it seems in the case of SUV's) be a greater factor in rolling the vehicle than just a steady state lateral acceleration scenario. Similarly, the chance of the car being driven at its maximum with students rather than professional drivers does seem very unlikely.

Indeed go-karts are still controllable despite their short wheelbases, I think I maybe overstated un-drive-able, maybe reduced stability would have been a more fitting statement, either way, I think I should be tying in steering ratio and geometry considerations to match the wheelbase since a 'faster' ratio will be needed to catch the slides as the car will rotate faster and also a longer wheelbase = more steering lock necessary to turn a given radius.

I will take your advice and update this thread as I go through the stages you have listed (I have a feeling I'll be getting stuck at stage 4! (probably earlier than that actually)).

I did check the seminar dates, the closest one to me (Oxford) is listed as November this year, I will look into it.

Once again, thank you for taking the time to construct such a detailed response.

------------------------------------------

Z, firstly, thanks for taking the time to help out (not for the first time either I might add!)

There is no harm in being blunt, I much prefer it to dancing around the point and it moves everything along at a faster pace.

You are correct in the time management issue, this is exactly what happened last year, the plan was to have a car finished a month in advance, they finished the car at the competition! We have put in place steps to ensure that wont be repeated this year.

Likewise, I agree with the simple car concept but the point where I disagree is on the aims. We all want to win, always, over the past 2 years I've had 4 projects which have been effectively mini competitions so of course I would like to win outright but in those competitions the field was equalized, that is not the case in FSAE for various reasons which are not the fault of anyone but it is important to remember that is indeed the case. I will elaborate further on this at the end.

I have read both the Reasoning thread and the Suspension Design thread, I haven't checked the Engine thread but I doubt it will make much difference to my situation since the engine choice is fixed by the supervisor.

I don't disagree that the team structure works against this, I admit and know that it does but again, it's important to know the situations which have caused this and why they are non-negotiable and cannot be changed.

I will definitely keep blogging the build providing I feel that there is something to be gained from doing it, if this thread turns into just another argument (like most on here do) then I just wont bother and everyone loses so as long as it stays civil and there is interest I will update it :)

Thank you for taking the time to reply and throw your thoughts into the ring, you like Claude have made me go back to considering 'the big picture'.

------------------------------------------

As has been pointed out I have so far failed to lay out the main goals I and the team have so hopefully this next section will resolve that matter.

The big picture

Last year we placed 77th at FSUK, we missed acceleration and skidpan because our diff carrier repeatedly ripped out of the car whilst trying to pass the brake test, we failed to complete either the sprint or the endurance within the time limits and handed paperwork in late. All of this because people did not fully understand the competition or the initial goals fully. The goal was to build a car which would place in every event, the team failed in that objective. Why? Organisation and poor car performance.

Deadlines were missed because people failed to understand the implications of missing them and the cars performance was poor because the analysis and understanding was poor, every time the analysis was incomplete the standard response was to beef up the components to a stage where they thought they would not fail. As such the car used M8 bolts, rod ends and spherical bearings everywhere, the tubing sizes were too conservative and the car ended up weighing 290kg (once all the diff reinforcement had been carried out) WITHOUT DRIVER! Yet the car still failed.

Our main aims are: slash the car weight to at least 220kg; improve the cars responsiveness; meet all our deadlines; get testing as soon as we can; finish inside the top 20 and to make the best use of the equipment we have available whilst furthering our own understanding. Due to various reasons it is not possible for us to sell parts in order to purchase new ones, I wont go into these here but lets just say it is not up to me or anyone in the team. Likewise, for the purchase of new parts, they have to go through a long and complex process before receiving approval and the order paid.

As such, our engine is fixed, it is the Honda CBR600RR 03 model, we are told the chassis must be a spaceframe, the wheels are 13 x 6 and our tyres will be the Avon's, our diff is the Drexler FSAE model and our brakes are 4 pot AP Racing Calipers with motorcycle discs. The engine is a definite weak link as it weighs roughly 60kg without considering the diff, driveshafts, chain,etc and we don't make good use of the power it has.

These are the constraints we have to work within (there are more but non spring to mind right now) I believe we can still fundamentally build a good car around these parts provided that they are integrated properly into the design and we make use of their strong points whilst recognising the weaknesses.

But in reality the main objective I and most of the team members have is to actually learn something! If we get to the competition, finish inside the top 20 and I feel like I know no more than I do now then I will still feel like we have failed, yes of course we want to win or at the very least place in a position we can be proud of but in my eyes it must come from having learnt what it takes to build a good car and not from gut feeling of 'what we think will work'.

Charles Kaneb

10-26-2014, 09:30 AM

600cc motorbike engine, tube frame, 13" wheels, Drexler are the starting ingredients for the Missouri S&T cars, winners of the autocross at Lincoln 2012 and 2013. Lots of fast cars use 'em. The weight of the engine makes it easier to get the weight distribution right. Don't second-guess it too much. If you're racing in July you need to be running at racing speeds in May which means a complete and running car in April.

Claude Rouelle

10-26-2014, 10:47 AM

Charles,

Adding weight to get to the ideal weight distribution? Patch on patch? You can get a light car with the ideal weight distribution. Many teams have prove it before.

10-26-2014, 10:07 PM

Christian,

More BLUNTNESS follows...

But in reality the main objective I and most of the team members have is to actually learn something!...
... yes of course we want to win ... but ... it must come from having learnt what it takes to build a good car and not from gut feeling of 'what we think will work'.

Very sadly, it is the above attitude that will see you repeat last year's performance this year.

I know that this comment doesn't seem to make sense to you, but it is true.
~o0o~

Last year we placed 77th at FSUK, we missed acceleration and skidpan because our diff carrier repeatedly ripped out of the car whilst trying to pass the brake test, we failed to complete either the sprint or the endurance within the time limits and handed paperwork in late. All of this because people did not fully understand the competition or the initial goals fully. The goal was to build a car which would place in every event, the team failed in that objective. Why? Organisation and poor car performance.

Deadlines were missed because people failed to understand the implications of missing them and the cars performance was poor because the analysis and understanding was poor, every time the analysis was incomplete the standard response was to beef up the components to a stage where they thought they would not fail. As such the car used M8 bolts, rod ends and spherical bearings everywhere, the tubing sizes were too conservative and the car ended up weighing 290kg (once all the diff reinforcement had been carried out) WITHOUT DRIVER! Yet the car still failed.

I am sure that last year's students also "wanted to learn". But, clearly (!!!), NO ONE WAS TEACHING THEM!
~o0o~

I had pulled out quite a few of your quotes that I was going to go over in detail (eg. all the theoretical details that you brought up). But I think it better to just sum this up as simply as possible.

* LITTLE LESSON - The main lesson you should have learnt by now is that planning to finish "a month in advance" results in complete and utter failure. Your current plan to finish two months in advance will result in a mere utter failure.

If you really want to learn anything about VD, etc., then you MUST have the car driving at least FOUR MONTHS before comp. There will still be a mountain of work to do after that.
~o0o~

* BIG LESSON - Many long-time ex-FSers will tell you that their deepest understanding of VD, or engine, or whatever in FS, only came to them many years AFTER they finished their last competition. You should realise that this whole education process is not a linear one of,
Learn-some-theory -> use-theory-to-design-a-car -> build-car -> race-it -> collect-trophies.

Real education DOES NOT WORK LIKE THAT.

This is probably contrary to everything that you have ever been told by your modern teachers, but in real-world, old-school education you;
1. First learnt HOW to do it, by DOING it...,
2. Then, much, much later, you discovered WHY you did it that way.

You can only "understand" WHY, by first "knowing" HOW. And you can only know HOW, by actually DOING it.

(As I said, contrary to everything you have ever been told... Criticisms welcome... :))
~o0o~

So, get a working car built ASAP.

You might start this process by posting as many concept sketches as you can come up with here, and then consider the reasonableness of the criticisms that the sketches receive.

The very first of the concept sketches should only show the locations of the major components. The most major component is the driver. So start with the "ergonomic concept sketches".

Err..., you do have your "ergo-rig" built already, don't you???

Yes, of course, you must have this built by now. So, perhaps start with photos of the driver in their preferred position in the ergo-rig, and with the engine and four wheels in their proposed positions.

Z

Jay Lawrence

10-26-2014, 11:26 PM

Christian,

Excellent thread so far, thanks for that.

Just wanted to re-enforce the 'build it early' sentiment. 2 months is NOT enough. Something like 4 months is more applicable and instead of saying "we're going to build it as early as possible" you set a date and remove all obstacles to hitting that date. This may sound impossible but if you approach each part with "is it actually required and will it cause us to miss our drive date?" then it is achievable. I'm talking here about items that people will typically want to play engineer with (turbos, push/pullrods, wings, fancy electronics, etc.).

You have been given some items to build around. This is not a bad thing and plenty of teams have been successful with your ingredients (including UoW, though we've had many different diff types over the years). It should also help to speed up the process because you are wasting less time choosing things that your team might not fully understand. If you feel like you don't have a solid enough understanding of tyres and how to build around them, build something in the ballpark and include plenty of adjustment (different mounting holes, adjustable rod-ends, swappable A-arms/geometry, different springs, etc.). The season will be gone before you have a chance to fully develop an "optimum" package (and inevitably the rest of the team will have also "optimised" and when you bolt it all together you end up with <<<< sum of the parts).

Sorry if I'm preaching to the converted, just figured I'd add my 2c ;)

ChristianChalliner

10-27-2014, 03:19 PM

Z,

Ok, If I read what you've said correctly then the point you are getting at really is that my mindset is incorrect?

I wont argue that you're wrong because maybe you are correct, in which case, how exactly would you prioritise your aims?

One thing I most certainly agree on is that the learning process is not linear and also that I've learned far more from things going wrong than I every have from things going well, it's just a shame that when things go wrong it tends to be rather painful for those involved!

It appears that the main point from everyone is to get a car running as soon as possible, which is great and would be ideal of course but I still have to do a base design which is at least competent before I can even get to that stage, I have taken some of Claude's advice with regards to simple sims rather than going straight to cad so I will get back once I've made some progress on those.

I did create a very basic OptimumLap sim with a 280kg car, the 2014 Michigan autocross course and base friction parameters swept from 1.35 to 1.65 both laterally and longitudinally resulting in the following:

Fy Friction = 1.65, Fx Friction = 1.65, Laptime = 59.93
Fy Friction = 1.65, Fx Friction = 1.35, Laptime = 64.37
Fy Friction = 1.35, Fx Friction = 1.65, Laptime = 61.68

So from base (1.65, 1.65) reducing the Fy friction to 1.35 increased the laptime by 1.92 (roughly +3%), reducing the Fx friction to 1.35 increased the laptime by 4.44 (roughly +7%) so from that basic sim it appears my initial suspicions that lateral events are much more important than longitudinal ones, so a setup biased towards good camber compensation in roll looks the way to go. How much more important seems a little difficult to quantify, to say twice as important seems a gross over simplification of the problem but maybe simple is the way to go.

I wont pretend we have a ergo rig, we don't, so far the driver environment guy has just been using the old car and repositioning the seat, pedals and wheel to get an idea of what most people have as a preference. But we obviously do have 4 wheels and an engine :p

Jay, I completely agree, everyone has jumped straight into detail design (myself included) which is not the way to go, obviously pulling everyone back to the 'big picture' stage might now take some effort but it can't hurt to try and is probably what is necessary.

Having set parts I actually find to be beneficial, as I have repeatedly told people, what we have are not bad parts, they have been put together as an effective package many, many times so it is not as though we are starting completely from scratch. I also find that knowing you have to use a set part prevents the urge to just go and look for something that is perceived to be 'better'.

As always, thanks for the thoughts :)

Ahmad Rezq

10-27-2014, 04:21 PM

You reached a good point to set a concept: " car which performs very well in corners".
but something to say by fixing engine and tires you will make your live harder especially if you don't have a good power train team you may end with a car which won't be able to run. so consider that.

Claude Rouelle

10-27-2014, 05:15 PM

Christian,

You wrote:

"Fy Friction = 1.65, Fx Friction = 1.35, Laptime = 64.37"
"Fy Friction = 1.35, Fx Friction = 1.65, Laptime = 61.68"

But you also wrote "my initial suspicions that lateral events are much more important than longitudinal one"

Did you mix them up?

Claude

ChristianChalliner

10-27-2014, 07:03 PM

Claude,

I don't believe I have mixed them up, maybe it is my axis system which is different to yours. I have defined Fy as the longitudinal axis and Fx as the lateral axis as it were. If this still seems wrong to you then perhaps I have made a mistake somewhere.

That does remind me though that I must stop switching between various axis systems. Our CAD program defines x as the lateral axis (left positive if viewed from the rear of the car), z as the longitudinal axis (forward positive) and y as the vertical axis (upward positive) this may seem unconventional (it is not how I would have defined them) but it does mean that even if someone forgets they shouldn't be able to create a part in the wrong orientation (or export points incorrectly).

MCoach

10-27-2014, 07:39 PM

Christian, The SAE axis system, which is de facto around automobiles, is Fy is lateral, Fx is longitudinal and Fz is up/down.

https://law.resource.org/pub/us/cfr/ibr/005/sae.j1733.1994/sae.j1733.1994_004_01.jpg

Z+ is up or down depending on who you ask, but traditionally Z+ is down because it was defined by aeronautical engineers.

Aligning your CAD design software with something like this (or perhaps the ISO designation if more comfortable?) will help standardize everything in design and manufacturing.

10-27-2014, 11:18 PM

Christian,

First up,
X = longitudinal (accelerating and braking forces),
Y = lateral (cornering forces),
Z = vertical (gravity and aero forces).

In the whole wide world, this is the only "standard" that is actually quite STANDARD (cf. drive on left/right of road, measure with metric/imperial, etc...).

PLEASE, PLEASE, PLEASE, everyone, try to stick to above!!! :)

(As for +/- directions, and position of the origin, I won't even try...)
~~~o0o~~~

Back to FS VD...

Question by Christian: "... how exactly would you prioritise your aims?"

Answer from Z (page 1): "To repeat my mantra, at this stage your Team's goal is to build a four-wheeled-chair that can propel itself and the driver at an average speed of 50+ kph, over a distance of 30 km, WITHOUT FALLING APART."

As noted by myself and many others here, the above task is not as simple as most students first think.

Hence you should PRIORITISE A "FIRST DRIVE" DATE that is a good FOUR months before comp, just so you can achieve that "average speed of 50+ kph" at the comp.

Importantly, DO NOT think that you have to have a really good understanding of VD, or of tyres, or of engine-tuning, or of any of those racecar things, BEFORE you start the design. In fact, do not even expect to have a really good understanding of any of those things when you finish the comp.

Instead, you should accept now that much of what you will be doing over the next EIGHT months (yep, time is running out!!!) will be like a blind man searching a darkened room for a black cat ... that isn't there! You, and all the other Team members, just have to put your heads down and work to the above goals.

Namely, DRIVEABLE CAR EARLY MARCH. If diff mounts rip out in mid-March, then work harder until the problem is fixed. Repeat until you can consistently cover those 30 km at average of 50+ kph...
~~~o0o~~~

Some detail stuff below, but more BLUNTNESS now (sorry, but hopefully worth it in the long run... :))

I had a quick look at the Aston Uni FS Team website, and it is worse than I imagined.

* The Team has competed at FSUK every (?) year since 2002, so is one of the MOST EXPERIENCED Teams in the UK. Ever.

* The amount of CarbonFibre and CNC-machining in the photos indicates one of the BEST RESOURCED Teams in the UK.

BUT!!!

* No indication of any significant success. Ever.

* No indication of significant knowledge transfer.

* Much useless complexity (eg. glued CF-tube wishbones, +++).

* Atrocious Ackerman on one year's car. And much more...

Bottom line here, is that this Team has a deep CULTURAL problem. Many, many, Teams suffer from this same problem. It is a case of locking yourself into a never-ending loop of underachievement. I have summed this up in the past as "polishing a turd".

M.C. Escher knew this process well. Note how one sub-team is continually INCREASING horsepower, and torsional stiffness, and all the other things that should be increased, while the other sub-team is continually REDUCING mass, etc., etc...

http://wac.450f.edgecastcdn.net/80450F/965kvki.com/files/2013/07/escher1.png

Ahhh, yes..... Non-stop progress, year after year after year... :)

But, look on the bright side, Christian. You can be the hero who achieves everlasting fame and glory because you freed Team-Aston-FS from this terrible prison. All you have to do is get the car built early!

(Note that this may require some diplomatic negotiations with your Supervisors. I suggest you ask someone more knowledgable than me for advice on this subject. Geoff?)
~~~o0o~~~

Prioritising big-picture VD stuff.

Most of your big decisions have already been made. This means that extensive Simulations are not necessary now, which is good because you can save time there.

The 13" wheels/tyres and four-cylinder-engine make outright victory much harder, but a top-ten at FSUK is still quite achievable. The tube-frame is NO handicap at all. If everything is running well a month before comp, then you might think about some quickly cobbled together aero. (<- DO NOT overthink this, so NO CFD!!!)

For now, your aim is to minimise the junk that is usually piled onto these cars! So SIMPLE suspension, SIMPLE frame, etc. ALL HEAVY PARTS TO BE MOUNTED LOW AND CLOSE TO THE CG. Putting this another way, you want minimum parts count, and squash everything that remains downward and together.

I would aim for minimum wheelbase (+5 to 10 cm to cover for cock-ups, or last minute changes) and driver's feet on front-axle-line. You probably won't manage this, but avoid unnecessary length. A round number of 1.2 metres for F&R track is good enough. "Optimising" these numbers will make very little difference to your overall performance. Wasting time on the optimisation process will give you the same result as last year.

Post concept sketches ASAP, and be prepared for Grumpy-Z to say "NO, NO, no, no, no.... you can do better...". The better the job you do at setting the correct direction now, then the quicker you will reach your destination. Final concept sketches (ie. topologically correct) end of November. Final detailed drawings (ie. with all dimensions), and hence first cutting of metal, by Xmas?
~~~o0o~~~

Some slightly more detailed stuff, though might be helpful to know now.

Here is one of my posts from the "Caster/Camber/Steering shims" thread (http://www.fsae.com/forums/showthread.php?5332-Caster-Camber-Steering-shims&p=92714&viewfull=1#post92714) from back in 2005. This discusses the range needed for these parameters, and their tolerances (I called it "accuracy" back then).

Given that earlier you said,
"Similarly, I was pondering the thought that all systems will have compliance to some extent so maybe analysing and 'tuning' the compliance may be more beneficial to car performance than just saying "well if I make it as stiff as possible it will be negligible" because in reality I'm pretty sure that the compliance can't/wont be negligible.",
it is worth asking yourself why I suggested those particular tolerances.

I can answer that question later if you want, but briefly for now, SOME COMPLIANCES CAN INDEED BE NEGLIGIBLE. (In fact, there have been whole, long-winded, FSAE/FS theses written on just that issue, applied to chassis torsional stiffness.)

It is part of the deep understanding that you might get much later that says that there are some things that you really DO NOT HAVE TO KNOW. (Here, you DO NOT have to know exactly how big the compliance is, just that it is "negligible".)

Z

Claude Rouelle

10-28-2014, 12:47 AM

Christian,

Vehicle Dynamics and CAD are not necessarily the same coordinates

But OK now we have erased a communication issue. Good

ChristianChalliner

10-28-2014, 04:05 AM

Noted on the axis system, I'll use the SAE definition from now on :)

Some very quick sketches, yes they are on CAD, why? because I could change the sketch faster than I could draw a new one by hand.

The crossed rectangles represent Springs/Dampers.

http://i1296.photobucket.com/albums/ag13/challicm/Sketch1DASD_zps87f4738c.png

Advantages - Simple (aside from creating the longer spring perch), CofG is lower than current arrangement, parts count is lower (compliance reduced as lower number of bearings?) design time potentially reduced as no time spent designing rockers and manufacturing.

Disadvantages - Motion ratios are fixed in design and will probably result in digressive springing (which is a topic for debate, does it matter, doesn't it? I'm not so sure). The new spring perch will be difficult to make and will potentially have to be rather large to prevent buckling.

http://i1296.photobucket.com/albums/ag13/challicm/Sketch3PullrodsactingasPushonthefloor_zps36ee34ae. png

Advantages - CofG is low down, could only be lower with a pull rod under the floor (The reason I've not done this is because I'm pretty sure the valving in the damper will be backwards (as in compression is a pull, rebound is a push) and I don't know if we will be able to get the shocks re-valved (yet!)). Other advantages are that the motion ratio can be altered and digressive, linear or rising rate springing can be achieved with the rocker design.

Disadvantages - As you can see, it makes life difficult with the footwell template, again more complexity, more nodes to reinforce, larger forces through the 'pull rod' due to the angle, etc. Probably more!

http://i1296.photobucket.com/albums/ag13/challicm/Sketch2Pushrodsuphigh_zps7ac0d560.png

This is basically last years arrangement.

Advantages - Similar to above but lower pushrod forces compared to the pull rod.

Disadvantages - Highest CofG of all 3 systems, probably the highest overall weight, complexity,etc

There's probably a lot more I've not mentioned but those are which spring to mind straight away.

Anyway, onto answering some of Z's points:

I know the task isn't a simple one (since last years team failed to achieve it) if anything it's easily the hardest part. The problem is that the project has (and always will be) a third year project so it has to 'fit' with what the university describes as a project which it defines as a full year. So inevitably most students see it as "well I have the full year I can put it off for a while" which is clearly wrong! But you try telling that to someone in October that you've never met and see if they believe you...

We have competed every year (except 2013) yes we've never had any real success, our highest position was 29th in 2009. Yes there is absolutely no knowledge transfer what so ever but we are working on solving that (by keeping proper handover documents and keeping in contact with previous students). Yes for some reason there was an obsession with carbon in the past which resulted in many very heavy cars because of excessive use of billet in the monocoque's due to poor understanding of load paths, etc. With regards to Ackerman I already know Z, it's one of the reasons I want to put the tie rod pickups behind the axle centreline this year.

Looking forward to your thoughts on my sketches :) and I will have a think about why you suggested those tolerances...

onemaniac

10-28-2014, 09:38 AM

It appears that the main point from everyone is to get a car running as soon as possible, which is great and would be ideal of course but I still have to do a base design which is at least competent before I can even get to that stage, I have taken some of Claude's advice with regards to simple sims rather than going straight to cad so I will get back once I've made some progress on those.

Optimum G claims that OptimumLap will simulate lap times with 90% or better accuracy. At first it sounded strange to me because it's a point mass sim, it doesn't consider all that complex suspension geometry, springs and dampers, load transfer etc etc.

BUT, given the fact that Optimum G has confirmed the accuracy through testing, we may say while the 10 input parameters stay the same, the worst design can still be 90% as fast as the best design (within 'acceptable' range I suppose, especially with compliance issue.) IF DRIVEN BY A COMPUTER.

I think the biggest loophole in FSAE is driver training and the second is the stability of the cars. If you look at competition results, the numbers tell us the fastest car around the skidpad barely maintains 1.4G of average lateral acceleration, with wings.
That's how far away FS drivers are from pushing the car to its limit.
The driver needs to be fixed through testing and stability needs to be sorted out through testing as well.

I'm not saying you should neglect details in design and just build something. but my point is that you should aim to spend the same amount of time testing the car and training the driver as you'd spend on design and build.

ChristianChalliner

10-28-2014, 01:14 PM

Interesting thoughts onemaniac,

Your point of spending as much time testing as designing/building makes sense, I actually put forward some of the points raised to a few team members today and what I remember most was the chassis guys comment "Yeah I get that but I want to design it right to start with" so you can see the mentality we've had instilled in us here :p

I also updated the previous post, let me know if you can all actually see the sketches. I may have some more for you tomorrow from the chassis guy too.

Jan_Dressler

10-28-2014, 09:34 PM

http://i1296.photobucket.com/albums/ag13/challicm/Sketch3PullrodsactingasPushonthefloor_zps36ee34ae. png

Advantages - CofG is low down, could only be lower with a pull rod under the floor (The reason I've not done this is because I'm pretty sure the valving in the damper will be backwards (as in compression is a pull, rebound is a push) and I don't know if we will be able to get the shocks re-valved (yet!)). Other advantages are that the motion ratio can be altered and digressive, linear or rising rate springing can be achieved with the rocker design.

Disadvantages - As you can see, it makes life difficult with the footwell template, again more complexity, more nodes to reinforce, larger forces through the 'pull rod' due to the angle, etc. Probably more!

Think 3D and install the shocks longitudinally, directed to the back, with the pullrod design? CoG low down and nearer to the middle of the vehicle, and shocks not interfering with the template... Just a thought.

I know, Z will hate me for the CF A-arms, pullrod, monocoque and unnecessary complexity visible in this picture ;)

http://www.highspeed-karlsruhe.de/images/fahrzeuge/F-107//F-107_rechts.jpg

10-28-2014, 10:02 PM

Your point of spending as much time testing as designing/building makes sense, I actually put forward some of the points raised to a few team members today and what I remember most was the chassis guys comment "Yeah I get that but I want to design it right to start with" so you can see the mentality we've had instilled in us here.

Christian,

Ooooo..... I think the above could be your biggest problem... :(

As so many here have said, it is of utmost importance that you get a driveable car sooner rather than later.

So, what to do?

I am the last person to advise you on this (my methods are much too old-school!). Perhaps try to convince as many other team members of the importance of an early build (= everlasting glory!), and then use "democratic pressure" to, err..., "encourage" the slackers to keep up. There might come a time when other Team members will have to step in and "help" finish off a particular part of the car. Basically, tell any "weakest links" that the rest of the Team wants to enjoy some success.

Does anyone else have some more new-age-ish acceptable advice?
~~~o0o~~~

Front-View Suspension Sketches.
========================
The Direct-Acting-Spring-Dampers are more than good enough. (Edit: And you can lower the CG by having the top-SD-mount quite a bit lower, perhaps at top-SIS height, so about 300 mm above ground...)

In FS conditions there is NOTHING to be gained from rising/linear/falling rates via rockers. Rising rates can be had through bump-stops (the best way, because most adjustable). Falling rates through droop-limiting (extensively covered by myself back in 2005, though very few people here get this yet). See the Cincinatti car at one of the 2014 US comps for a really good example of how to quickly adjust spring rates. (<- I can find these various links if you want.)

Your sketched wishbones suggest a FVSA Length of about 3/4 track-width. Going for the Lancaster-Link style suspension, with FVSAL = 1/2 track, has a lot of practical advantages. Perhaps most important is that it greatly reduces compliance issues, and also greatly simplifies the frame. (I recall discussing this before, but I lost all my PMs in the Great-Forum-Shift of 2013...)

Of course, using Beam-Axles all around ELIMINATES ALL CAMBER-CHANGE COMPROMISES during Heave, Pitch, or Roll. The camber NEVER changes! (Well, except for tyre squash, and steering-geometry.) But Suspension Kinematics are not very important in FS/FSAE. The LL style suspension has good enough Kinematics, and is very simple structurally. (BTW, the frame bottom rails can be horizontal and just above ground (ie. flat floor), with the LLs above them as they converge to the car centreline.)
~~~o0o~~~

"General Arrangement" Sketches.
========================
These are most important at this stage. So some "three-view" sketches (ie. Plan-View, Side-View, and End-View) of the whole car, showing bold outlines of driver, engine, and wheels, and lighter outlines of frame, suspension, and steering. There is really not much point going into small details until you have a good idea of this "big-picture".

A key design point here, that you will NOT get from any of the Simulations mentioned so far, is that you should try to squash the engine as far rearwards as possible. This means minimising the distance between engine output sprocket and diff, and possibly mounting the diff BEHIND the rear-axle line (eg. about 5 - 10 cm). This minimum engine-diff distance can be achieved with a gear-train (difficult, and probably best left for 2016, even if design starts now?), or a "Morse" (aka "Silent") chain, which can have very short centre distances. Talk to industrial transmission suppliers...
~~~o0o~~~

Enough for now.

Except you might want to remind your current Chassis-Guy of what happened the last time the Chassis-Guy wanted "to design it right to start with". :)

.. for some reason there was an obsession with carbon in the past which resulted in many very heavy cars because of excessive use of billet in the monocoque's due to poor understanding of load paths, etc...

Z

(PS. Jan, just saw your post. Do you think Christian's Team could pull that off in the next eight months, especially given their past track record? I mean, you crazy Germans just love getting up at 4 am so you can work a 20 hour day towards a deadline of "car first driving at 3:15 pm of Tuesday, week 31...". And you then meet that deadline! Precisely at 3:15...!!! :))

mdavis

10-28-2014, 11:17 PM

Christian,
Front-View Suspension Sketches.
========================
The Direct-Acting-Spring-Dampers are more than good enough. (Edit: And you can lower the CG by having the top-SD-mount quite a bit lower, perhaps at top-SIS height, so about 300 mm above ground...)

In FS conditions there is NOTHING to be gained from rising/linear/falling rates via rockers. Rising rates can be had through bump-stops (the best way, because most adjustable). Falling rates through droop-limiting (extensively covered by myself back in 2005, though very few people here get this yet). See the Cincinnati car at one of the 2014 US comps for a really good example of how to quickly adjust spring rates. (<- I can find these various links if you want.)

Z

It was 2013 where the car did reasonably well. The 2014 Cincinnati team took a lot of things for granted, and didn't understand how difficult it is to even build a car, let alone build a competitive one (and we weren't even competitive in 2013).

Christian,

As mentioned, get the car done as early as possible. You won't have the ideal solution (what is ideal, anyway?) the first time. Just pick some stuff and go with it. If you're worried about a certain quantity, design in some adjustability, and figure it out on track in the spring. If you don't have good drivers, you'll need time for them to get comfortable in the car anyway. The more time you can get your drivers in the car, the more points you'll gain. The car and driver are a system, you have to optimize both pieces. If you're not dealing with very good drivers, having a simple, easy to drive car with 4 months of testing time will be faster than a theoretically higher performing vehicle with 1 month (or worse, 0 time) worth of testing.

As for the chassis guy being worried about doing it right the first time, it simply needs to be stiff enough for this year. You need to get your team to think long term. If you haven't had a really successful year, you're not likely to win this year (possible, maybe, but probably not likely), so focus on building a good car that can serve as a springboard for your team for years to come. That was our focus at Cincinnati in 2013. It backfired in 2014 (the team thought they knew how easy we had it, but they didn't fully understand the dedication it took), but 2015 seems to be somewhat on track. They've got aggressive timelines, and are working towards them, even if they may have their goals somewhat backwards. As the grumpy old guy, I think they are focusing on the wrong things, but such is life. They'll find out in May whether or not their focus was right...

-Matt

ChristianChalliner

10-29-2014, 05:59 PM

Jan - I did think about that yes, just never got round to drawing it (plus it wouldn't have shown up well in 2D, my main concern with that arrangement was the difficulty of an elegant solution to sitting the rocker mount and damper top mount on chassis nodes. Or more aptly, how the chassis guy would create a node at those points without it looking extremely messy and being very heavy.

Composites are out of the question, why? we have no one with past experience of composites on the team and the learning process (as shown by the guy who did it last year) is long and as many have pointed out, time is not something we have.

Z - we're already working on it, we have another meeting tomorrow with the intention of weeding out any weak links or at least giving them 'master switch' projects as we like to call it :p

Regarding top mounts (and actually wishbone mounts too) we're running into a slight problem there, we're aiming to minimise the number of chassis tubes and with the side impact rules as they are it's pretty much fixing our upper arm nodes to a box between 300-350mm above ground level. Likewise tying in a SD upper mount to the tube running between fore and aft upper wishbone mounts puts the shock at a very shallow angle and results in low shock travel and velocity. Thoughts?

If there's nothing to be gained then why the debate and the extensive coverage of the falling/linear/rising rate argument?

As far as I can tell spring rate changes should be pretty fast given the ease of accessibility anyway but I'm always open to something even faster :)

To be honest the sketch was just that, a very quick sketch so I wouldn't read too much into the arm angles and FVSA length from them, we've had the discussion about Lancaster links before. The main thing I remember being extremely complex about the whole thing was the arm fabrication, I also remember that Lancaster dropped the arrangement last year which has me questioning as to why... I'm not convinced by the argument that it greatly simplifies the frame though because to actually achieve the 1/2 track FVSAL the IC would be dead on the car centreline, so you're actually ending up with a FVSAL shorter than 1/2 track if you were to mount them a 'conventional' distance from the centreline.

I don't see how what you say about beam axles is true, how does it eliminate a camber compromise in one wheel bump or even roll? and you've then got to restrain its sideways motion, etc so there's that.

What will please you though is that we're building an ergo rig tomorrow and that I wasn't actually the one to suggest it.

I looked up a silent chain, seems simple enough just need to find someone to cut the sprockets, we were already going down the route of compressing the back of the car anyhow, although our reasons were mainly to reduce frame weight and to make a diff carrier which actually worked by bolting it to the back of the engine (via a plate medium).

The chassis guy also requested that I post a sketch of his up here (I tried to make him create an account but he wouldn't, I can't possibly think why :p)

http://i1296.photobucket.com/albums/ag13/challicm/chassis_zpsd38a3295.png

Matt - That's true and that's what we're working towards, since it's been made abundantly clear to me that the car needs to run much further in advance than originally anticipated we have tried to push on people more to concentrate on the big issues rather than the fine tuning (since they're probably fine tuning the wrong things anyway).

Claude (If you're still checking in on this) - I did look at the yaw moment diagram in the OptimumG folder and I think I understand the idea of it, the limitation I have is the tyre data again but I think I'll still learn something from it by creating one generated from a completely random tyre curve I've made up so I'll get onto that!

I really mean to keep doing these things but every time I sit down to start I get other members asking me questions! It seems like I spend at least 90% of my time talking through ideas with people and less than the remaining 10% actually working on my own things! :( Hopefully it pays off.

10-29-2014, 11:03 PM

Jan,

I hope you realize my comment about "crazy Germans..." was a compliment (best I can do... :)). It would be scary if one of your Teams ever decided to build a brown go-kart with a really GOOD aero undertray!
~~~~~o0o~~~~~

Matt,

2013? How time flies. Seems like yesterday. (And thanks for the spell-check, 2 n's, 1 t, was too lazy but will try to remember. :))
~~~~~o0o~~~~~

Christian,

"It seems like I spend at least 90% of my time talking through ideas with people and less than the remaining 10% actually working on my own things! Hopefully it pays off."

It will, in a big way! Setting the correct direction at the beginning of the journey gives you the shortest route to the final destination.

Also, some all-day BS-ing (Brain-Storming?) sessions, ending amicably, probably with beer and pizza, are a good idea here. It is one of the key points of Geoff's "Reasoning..." thread (though often overlooked) that regular and ENJOYABLE Team meetings are a big ingredient to success. Who'd have guessed that beer and pizza can make your car go faster!?
~o0o~

"... a SD upper mount to the tube running between fore and aft upper wishbone mounts puts the shock at a very shallow angle and results in low shock travel and velocity. Thoughts?"

These are tiny cars. A Motion-Ratio of 1/2 or less is NO problem. You simply use thicker wire on your springs and a few extra clicks on your dampers. I have asked this question many times before, but have yet to hear of any Team that MUST run its dampers at their stiffest setting. In other words, there is plenty of scope to move to lower MRs. As an added bonus, using dampers with 50 mm stroke will give you 100 mm of wheel travel, which is good should you ever do any testing on tracks with REAL bumps.

A key point to understand about FS/FSAE suspension design, is that it is an ENTIRELY ACADEMIC EXERCISE. As stated many times before, cars have won these competitions with virtually NO SUSPENSION MOVEMENT at all, other than from their uncontrolled compliance! (Pat likes to give me "infraction points" for mentioning this, but it is a fact.) I have been suggesting to the Organisers since 2005 to put many real bumps on the tracks, so that it becomes a real suspension design contest, but nothing yet...
~o0o~

"If there's nothing to be gained then why the debate and the extensive coverage of the falling/linear/rising rate argument?"

As noted above, this is a PURELY ACADEMIC ARGUMENT, akin to "how many angels can dance on the head of a pin?".

If, say, rising-rate was really useful in FS, as it genuinely is on Moto-X bikes, then we should see a lot of winning FS-cars with really aggressive rising-rates. But rising-rates on the corner springs leads to excessive CG rise during cornering (this is different to "kinematic jacking"). So a great many circuit racing cars use "droop-limited" springs, which give an aggressive falling-rate. This works poorly over bumpy roads, but gives a slight advantage through SMOOTH corners (ie. CG lowers).

Bottom line here, is that like most of the "esoterica" in FS/FSAE, none of these arguments are correctly reasoned through theoretically, nor are they properly demonstrated in practice. For example, here is a thread from 2005 discussing zero-droop (= falling-rate) suspension. (http://www.fsae.com/forums/showthread.php?4047-zero-droop-behaviour) In particular, note the lack of a clear theoretical understanding of the issue, and how welding some chains onto the suspension can sometimes, err..., sort of, help it go faster...
~o0o~

"... Lancaster links ...
... I'm not convinced by the argument that it greatly simplifies the frame though because to actually achieve the 1/2 track FVSAL the IC would be dead on the car centreline..."

Yes, that is where I would put it. A bit like these Semi-Leading/Trailing-Swing-Arms (http://www.fsae.com/forums/showthread.php?8950-Suspension-Design&p=45363&viewfull=1#post45363).

To ease yourself into the structural design you could fabricate the Swing-Arms like double-wishbones, but with the two wishbones welded together at their inner-ends, making one SA. At the front this deletes two BJs, and hence the compliance that comes from them. Note that since your driver's feet will likely be in front of the SA's front members, it is probably best to have these arms passing ABOVE the bottom chassis rails (ie. the SAs enter the footbox through its walls). This gives a very easy to build "flat-floor" chassis (see below).

At the rear the SA should BOLT directly to the upright, via shims for camber and toe adjustment. This eliminates 5 (or 6) BJs per rear corner, greatly reducing compliance issues.
~o0o~

"I don't see how what you say about beam axles is true, how does it eliminate a camber compromise in one wheel bump or even roll? and you've then got to restrain its sideways motion, etc so there's that."

I have covered this extensively before, but briefly, the "camber" to be controlled is the angle between the wheel and the patch of road immediately below it. This should be close to 90 degrees (so tyreprint "flat" on road).

For very short wavelength, high amplitude "corrugations", it is the position of the wheel wrt the peak or valley of the bump that determines this angle (ie. imagine end-view, and wheel either to left, or right, of peak/valley). A passive suspension can do nothing to control this.

For much longer wavelength "undulations", such as super-flat FS tracks, the road surface can be considered a straight-line drawn through the L&R tyreprints. It follows that a beam-axle then gives the best camber-angles at any time...

Quite a few Teams are now moving to beam-axles (at least in Oz). They make a lot of sense. But the LL/Swing-Arms are also more than good enough, and also give a very simple and robust car overall.
~o0o~

"...we were already going down the route of compressing the back of the car anyhow, although our reasons were mainly to reduce frame weight and to make a diff carrier which actually worked by bolting it to the back of the engine (via a plate medium)."

Yes, good thinking!!!
~o0o~

"The chassis guy also requested that I post a sketch of his..."

http://i1296.photobucket.com/albums/ag13/challicm/chassis_zpsd38a3295.png

I know this is only a very early draft, but already TOO COMPLICATED (because very derivative!).

I would suggest,
* Start with a flat-floor (with bottom-side-rails having at most one bend at the MRH, for slightly coffin-shaped floor in plan-view).
* Four bulkheads at most (ie. 1. front-IA, 2. FRH, 3. MRH, 4. rear-of-engine).
* Make FRH narrower at top (so more like the top of MRH) for better driver sight-lines.

Z

Jan_Dressler

10-31-2014, 02:45 AM

ChristianChalliner

10-31-2014, 10:07 PM

We had another meeting on Thursday which seems to be the only day the whole team actually turns up, that needs to change and fast. But anyway, in order to give people some an idea of scale I taped out a 1530mm wheelbase, 1100mm track (front and rear) and then placed sections of cardboard to represent some components. The idea was that people would then have a good idea of the parts they were making and the 'boxes' they fit into and how they would interact with each other.

http://i1296.photobucket.com/albums/ag13/challicm/387DF3C7-62AD-4149-8231-403AA1E0B48F_zpsyg9mt5vx.jpg

http://i1296.photobucket.com/albums/ag13/challicm/DB752EDF-D505-428D-9E98-9F035CCEA3FB_zpsaapbuynl.jpg

http://i1296.photobucket.com/albums/ag13/challicm/5BA13A96-FD83-4F32-9B53-4BB47F448D77_zpswrdudua6.jpg

What struck me the most was how compressed the back of the car was actually going to be, I was one of the most vocal in pushing for a shorter rear to reduce the frame weight but I was still surprised at how short the 'mock up' made it look.

I did some thinking about the rising/falling/linear rate debate and thought that a progressive rate spring would possibly be an easy solution to the falling rate problem but what actually is the advantage of rising rate? I don't really see it over such a short travel. I'll have to prove the other things Z mentions to myself first before I believe them as I can't visualise it in my head.

Z - Some comments from the chassis guy:

"The front roll hoop cannot be narrower otherwise we will fail the template test. I am also working on reducing the number of members with the intention of seeing if it is possible to use only the mandated tubes to make a stiff enough chassis. I don't understand what you are meaning by four bulkheads at most, I count a minimum of 5: IA, fore wishbone mounts, FRH, MRH, Diff mount/engine back. Also, the flat floor isn't possible because of where Christian currently has the hard-points which would result in the driver sitting too high up."

I also tried out a few things and I was somewhat surprised.

I played around with a direct acting arrangement and ended up with a fair bit more shock travel than I was actually expecting to get, when I was drawing this I was thinking I would have around 20mm shock travel but it turns out it was actually closer to 30mm which isn't so bad given that the shocks useable travel is only 40mm. On second thoughts that means 1/4 of the shock travel isn't being used... hmm.

http://i1296.photobucket.com/albums/ag13/challicm/DAV2ABOVESHOT_zpsecd7848a.png

http://i1296.photobucket.com/albums/ag13/challicm/DAV2FRONTSHOT_zpsb1ef8689.png

http://i1296.photobucket.com/albums/ag13/challicm/DAV2ISOSHOT_zps547b3cab.png

Yes those rear arms are extremely long and are worrying me somewhat, however, I had to try it just to see if I could reach the main hoop with them since finding a suitable node for that inboard point is difficult without introducing more frame members. I can actually see how a beam axle might work at the back and I actually helped out with the design of a similar system for the eco car team we run here (much simpler than this, they don't care about the kinematics of their system :p). In essence it was two trailing arms with direct actuated dampers on the arms to give bump control but the pivot points of the arms were joined together by a torsion bar which was free to rotate in bearings giving some extra anti-roll stiffness. I was thinking if a similar idea could be adapted to this...

Jan - What you suggest wouldn't work for us as it is the intention that the front hoop has the lower a-arm node on it but still, it's an interesting idea I will look at to see if I can make it work :)

Me and the chassis guy are going to be working over the weekend so I'll sort some more progress pictures/ideas/etc tomorrow or Sunday.

P.S how do you embed photos on this forum? the attachment manager never seems to work for me.

Mitchell

10-31-2014, 10:38 PM

Ignoring the monoshock for now (although monoshock makes it even better...) You will not get a simpler or more accessible rear section of the car with anything other than a beam axle. If you can fabricate a chassis, you can fabricate a beam. This one is made out of 0.9mm sheet laser cut and folded. The -system- is lighter than the previous years although you do gain some unsprung weight, we didn't consider this an issue.

This is the rear beam behind the 2013 car.
398

And the completed rear end for comparison.
399
Lateral location is hidden behind the bottom of the shock, but it is just a cam follower bearing rolling in a machined slot.

I love what you are doing with the cardboard cutouts! This is an excellent exercise. Throw in an oil system, exhaust, fuel tank, radiator and you will learn more in 10 minutes than hours of cad. You have to be willing to push every mm you can. The diff could be further back, and the engine could be nearly touching it. Doing this moves the engine and driver back and also makes the car shorter.

mdavis

10-31-2014, 10:50 PM

Christian,

You may have shortened your rear frame, but it is still way too long. You need to move your MRH back towards the rear axle centerline. If I remember correctly, our better packaged cars (2008-2009), the MRH was ~12-14" in front of the rear axle centerline. With single cylinder engines (our team changed in 2012), this number gets even smaller. Your MRH looks like it is half the wheelbase ahead of your rear axle. Let me guess, your old car has issues putting down power? And lots of front weight bias?

Based on where your taped lines are, I would aim to move your MRH at least to the black tape line that holds your engine template to the ground... If you really want to shorten the rear end of the frame, it is possible, you just have to work towards it.

-Matt

ChristianChalliner

11-01-2014, 04:08 PM

Mitchell- When you're saying you gained some un-sprung weight how much was it that you actually gained? and how much do you think the overall weight changed by due to switching to the beam? A big killer for us is that our engine isn't dry sumped and the sump on the CBR is ridiculously tall, we've talked about cutting the pan and making it wider but shallower and baffling or gating it to prevent starvation but whether we get that done this year is another thing. If you're wondering why not just dry sump it's because there's a distrust of dry sump systems from the academia for some reason so that's a no go.

mdavis - The honest answer is that no one really knows how the old car handles, it was finished at the competition and only driven there, there was no chance to drive it post competition as we snapped an upright just by messing with the car in the workshop (they've been used for a couple of years and there was substantial fatigue cracking on them around the lower pickup) needless to say we weren't impressed. I have revised the layout today and pushed the diff further backwards, I've still left some space between the diff and engine for our rear plate to fit in.

http://i1296.photobucket.com/albums/ag13/challicm/84EBD129-3BB2-4D6F-93DE-89757713F83E_zpsxpucqd6z.jpg (Sorry about the picture).

Jan_Dressler

11-01-2014, 06:50 PM

A big killer for us is that are engine isn't dry sumped and the sump on the CBR is ridiculously tall, we've talked about cutting the pan and making it wider but shallower and baffling or gating it to prevent starvation but whether we get that done this year is another thing. If you're wondering why not just dry sump it's because there's a distrust of dry sump systems from the academia for some reason so that's a no go.

I do understand that partly... When I joined my team in 2007, we just switched to the PC37 engine. The same you are using. And yes, we too found out that the oilpan is extremely tall, and yes, there was a distrust in dry sumps too ("Team XYZ tried it and killed 6 engines, we cannot afford that!"). Dry sump is a lot of work, some thinking, extra cost, extra weight, yes. But if you do it right, you will have your engine (heaviest component of the vehicle besides the driver) at least 10, 12 cm lower. And dead reliable. And because the cylinder head is so much lower, you can put the seat further back. And the engine itself, more "under" the diff while keeping the same minimum chain length. And you have some freedom where to put the extra weight (oil tank).

Guess what, I was the "dry sump guy" these days, who designed the system. ;)
The car in the picture further up this page still used an evolution of it...
Your engine/oil guy should send me a PM. I will certainly not give a detailed "recipe" but I will tell him if he is on the right track, concerning sizing of scavenge pump, lines and so on.

Using the PC37 with stock sump is a bad joke. And cutting the sump, making it wider... CAN work, if you do it right (rotary oil pickup), but is more work and not as "safe" as a good dry sump system.

P.S.: Pictures in this forum, try it with the [ img ] [ / img ] tags (without the spaces) ;)

Mitchell

11-01-2014, 09:53 PM

Mitchell- When you're saying you gained some un-sprung weight how much was it that you actually gained? and how much do you think the overall weight changed by due to switching to the beam? A big killer for us is that are engine isn't dry sumped and the sump on the CBR is ridiculously tall, we've talked about cutting the pan and making it wider but shallower and baffling or gating it to prevent starvation but whether we get that done this year is another thing. If you're wondering why not just dry sump it's because there's a distrust of dry sump systems from the academia for some reason so that's a no go.

Change in unsprung due to the beam was <2kg. The chassis was reduced to the rules required roll hoop support and roll hoop support structure. There is no rear bulkhead, diff mounts straight to engine.

You can get an idea of how much weight was taken out of the chassis by this picture.
400

Unfortunate about the dry sump. To be fair the ones that seem to fail are the ones where people try and push them to the limit. The oil system we have was designed fairly conservatively. Oil supply is something that is not worth trying to squeeze the last 5% out of, we dont have a large budget and engines are expensive.

11-02-2014, 05:48 AM

Christian,

Most important first.

As Jan said, you can display the image on the Forum-screen by taking its URL-link (usually starts with "http" and might end with ".png" or ".jpg", etc.), and typing [eye-emm-gee] directly in front of it, and [/eye-emm-gee] directly behind it, with "eye-emm-gee" = "IMG". BINGO! The picture appears in the middle of your post.

This is an example of one of those things that you do not have to UNDERSTAND (I certainly don't, and will never try to), but it can be useful to KNOW a little of it. It is a not-entirely-standard standard that is used on many forums. Sometimes you MUST use upper-case for the codes inside the square-brackets, other times lower-case works. Usually excess spaces create havoc. Other useful codes are; I (italics), B (bold), URL (link), and QUOTE (fancy quote).

And I really miss the :mad: (mad) and :rolleyes: (rolleyes) emoticons on the older forum...
~o0o~

Back to VD.

I agree with Matt and Mitchell about moving the driver as far back as possible. Also agree with Jan that you should think about dry-sumping to lower the engine, which then lets the driver move even further rearwards. The dry-sumping is only difficult when you have NO IDEA of what to do. But Jan has said he can give your Team some guidance..., which is a good offer!

The IMPORTANT POINT here is that this big-picture issue of the distribution of the major masses of the car (ie. driver + engine, wrt 4 wheels) has a much greater influence on a car's VD than any of the other issues that most students dive straight into. For example, fine details of suspension kinematics, optimised frame torsional stiffness, shaving another n-grams of the brake-discs, etc., really amount to squat, compared with that major masses distribution.

For example, you have suggested starting with track-width = 1.1m. That would be quite good IF you have a lowish CG. But with a high-CG engine, maybe not? At Oz-2013 one of the four-cylinder cars (bad memory... UQ, Mitchell?) had a narrowish track and unusually high "RC"s, and spent much of its time up on two wheels through the corners. This was not conducive to driver confidence, so not the best lap times...

A simple fix to the above problem is to widen the track, perhaps just by fitting wheel spacers. Or lower the "RC"s (ie. lower n-line slopes). Or both. But this needs a car built and tested early, and a preparedness to make major changes just before comp.

Better to get the big issues right first.
~o0o~

The "chalk lines on the floor" approach is great. Well, here "tape lines", and conveniently on a floor with 1' square tiles! Keep doing this and more like it.

I suggest a 8' x 4' sheet of plywood about 15 - 20 mm thick that you can build up on. Also buy some lengths of softwood as used in house construction (eg. 40 x 90 DAR), and perhaps more plywood about 5 - 10 mm thick. Make plywood wheels, engine, seat, radiator, etc. You can do a "first draft" of these using your cardboard and 2" wide masking tape (works better than duct tape).

Get as many of the newbies involved in this as you can. This might be the best "knowledge transfer" they get. Also the above plywood "~ergo-rig" can be reused every year. Here is a link (http://www.fsae.com/forums/showthread.php?11850-Frame-Design-First-Car-IFS&p=121352&viewfull=1#post121352) to another of my recent posts on this sort of old-school CAD (Cardboard?-Aided-design). Also useful stuff on the first page of that thread.
~o0o~

"I played around with a direct acting arrangement and ended up with a fair bit more shock travel than I was actually expecting ...
... closer to 30mm which isn't so bad given that the shocks useable travel is only 40mm."

With only 40 mm damper travel, a MR = 1 (the experts' recommendation!) would have you failing Scrutineering! Ouch!!!

Having the DASD at 45 degrees to the wishbone gives MR = ~0.7 (=1/sqrt(2)), and ~56 mm wheel travel, which is only just legal.

DASD at 30 degrees (ie. very "laid down") gives MR = 0.5, and ~80 mm wheel travel. Good for a bumpy test track.

"On second thoughts that means 1/4 of the shock travel isn't being used... hmm."

As I have noted before, FSAE cars have won competitions with NO shock travel at all.
~o0o~

"... comments from the chassis guy:
...
The front roll hoop cannot be narrower otherwise we will fail the template test..."

I suggested narrowing the TOP of the FRH. Keep roughly the same width at upper SIS level, but bevel the corners off the excessively wide and square "shoulders" of the FRH. The current (draft sketched) FRH is simply following the current fashion. It has excessive mass up high, and the wide "shoulders" may (?) interfere with driver sightlines.

"... I don't understand what you are meaning by four bulkheads at most, I count a minimum of 5: ... fore wishbone mounts ..."

At this stage there should be NO ASSUMPTIONS at all regarding the type of suspension. The car may not have any wishbones! And if it does, then the front wishbone arms might attach to the front bulkhead (which would make a lot of sense!).

"... Also, the flat floor isn't possible because of where Christian currently has the hard-points which would result in the driver sitting too high up."

Again, this is "design by unjustified biases, prejudices, and preconceived notions...".

To restress all of this again, AT THIS STAGE YOU SHOULD ONLY BE THINKING ABOUT THE RELATIVE POSITIONS OF THE MAJOR MASSES (ie. driver, engine, wheels). All the other little details come later.

As such, when I said "flat-floor" I considered it obvious that this would lie under the driver and engine, being perhaps 30 mm above ground (to underside of floor). Suspension pick-up points are TRIVIAL LITTLE DETAILS. Sure, you will need them eventually. But you will also need an On/Off-Switch for the engine, and a whole lot of other little things.

Get the big-picture right first.

Z

ChristianChalliner

11-02-2014, 10:41 AM

Jan - Thank you for the offer :) We have a member who can possibly work on the dry sumping so if it's taken up then he will certainly be in contact with you with regards to his ideas. I completely understand where you're coming from in allowing the driver to sit further back, it's something that we've been fighting with! Currently, if we push the seat back the driver has to sit more upright which reduces the frame length and overall weight but moves the CofG higher, but how much higher? we don't know yet... it needs further analysis.

Mitchell - Looks good, one thing I don't fully understand from your pictures so far is how your mono-shock is actually actuated, I see you've got 4 links taking your beam to the main hoop and then the roll axis is where that bearing sits in the center of the chassis but how does the beam rotate upwards to actuate the shock if it's held on its axis by the bearing?

Z - I did try IMG tags initially but they didn't seem to work for some reason, it's a problem specific to this forum, I have no problems embedding photos on other forums.

I can see where you're coming from and it's something that has been mentioned before, if OptimumG's point mass simulation is within 10% and (to some extent) disregards suspension kinematics, assumes 50/50 WD, no wheelbase, etc then it stands true to reason that it's the big picture items which make the difference not the fine tuning of if you're running 1% or 5% of anti-dive. Before someone jumps down my throat I'M NOT SAYING they don't matter, just that other things are more important!

The problem is Z that I actually have to have some deliverables for my project so these issues must be focused on at some point and I also have check-ups at certain points over the year so I must do something in regards to these items early on to prove I'm actually doing something. I know, broken education system... etc, but if I go in and say well actually all I've done is said lets squash the car as much as possible and push the weight all the way to the back then that conversation only lasts so long...

I did also consider that yes the CofG is quite high but as you say by lowering the RC's this removes the lifting wheels problem but how low is sufficient? Again, analysis incomplete. The plan is to have a finished car by the end of February which should give sufficient testing, it also appears to be the case that this car and deadline is really being pushed by just 3 of us but if that's how it has to be then so be it.

It's good that you mention making a wooden rig as that's the plan for next week, it was the chassis guy that pushed for us to do a full 3D mock-up after we taped out the 2D one so we'll do that.

With regards to the DASD location, on my posted images the upper mount is inline with the upper wishbone mounts, as it turns out this actually gives quite good triangulation between all the wishbone mounts and the DASD mount so I think I'll keep with it as long as is feasible.

I wont move to Lancaster Links because I don't fully understand them and how we would integrate them into the chassis but what I am considering is the beam axle at the rear as it shortens the chassis dramatically and resolves the rear hard-points issue.

The chassis step is my fault but the intention was for it to be flat initially (and 30mm above the ground so we agree on something! :p), the decision to step it was driven by my desire to have the lower wishbone parallel with the ground, initially I thought this would give lower arm loads but now I'm not so sure, again, analysis incomplete!

We also had this idea for a pedalbox...

http://i1296.photobucket.com/albums/ag13/challicm/EDB2D855-7CB8-4FAE-905E-0BCFDD61A2CB_zpsfhwpd73b.jpg

Which removes the excessive length of this current one

http://i1296.photobucket.com/albums/ag13/challicm/723FF2A7-4093-4D5A-A34E-CDDB4938AE7D_zps2ikcrkgd.jpg

We also have an idea for the front of the chassis which we are drawing up currently so I'll upload that once it is done.

Jan_Dressler

11-02-2014, 06:24 PM

Jan - Thank you for the offer :) We have a member who can possibly work on the dry sumping so if it's taken up then he will certainly be in contact with you with regards to his ideas.
No problem, do that! :)

We also had this idea for a pedalbox...
This is a possibility certainly (and a certain team I happen to know very good did it just like that in the past), but keep the templates in mind... Depending on how long the assembly under the driver's feet is, the template would have to go over it, which means making your frame higher... Also, don't forget the fluid containers, which have to go somewhere ;)
Or think different. Placing the cylinders on both side of the pedal, but vertically, maybe...? Works, with some linkage... Just a thought :)

By the way, looking at your last picture, try to make the whole thing look a bit neater when it's finished. That doesn't make your car faster. But judges will like it. And one day, after you finished your thesis and maybe find some work in a small company that makes race (in my case rally) cars, you will find out that customers like things that look neat and tidy... Our Group R4 and N cars wouldn't need the carbon fiber and anodized alu "bling bling parts" to be fast. But they sell better with them. And you try to "sell" your car to the judges... Just my 2 cents.

11-02-2014, 08:48 PM

Christian,

Ah, good ... now I don't have to log-in just to look at pics!

"Mitchell...
... how does the beam rotate upwards to actuate the shock if it's held on its axis by the bearing?"

Mitchell's Team uses a "peg-in-slot" for the lateral location. The peg is (I guess from M's post) a needle bearing "cam-follower", and it rolls in a vertical slot, which thus lets the beam move in Heave. A similar system is shown on this "Twin Beam-Wing" (http://www.fsae.com/forums/showthread.php?1324-Beam-Axles-Front-Rear-or-both./page3) post on the "Beam-Axles..." thread. And similar systems were also used on the Mercedes-Benz "Silver Arrow" GP cars of the 1930s, and many others...

I am currently preparing a few more sketches for that "Beam-Axles..." thread that you may be interested in, should you decide to use a rear beam (err..., ready maybe next week...). You might also try looking up ECU's current car (ie. West-Oz team supervised by Kevin Hayward). I think they were at FSUK-14 (memory???) and are running a particularly neat bespoke four with rear-beam-axle. They use the head/crank/pistons/etc. of a sportsbike-four, but have made their own engine-cases that integrate a 2-speed(?) gearbox and final-drive/diff into a very compact package.
~o0o~

The main reason that everything should be pushed rearwards has to do with F:R% and "putting the power down" (as Matt described it). With a reasonably powerful four, and around 50%R, the car simply lights up the rear tyres coming out of slowish corners. All that power amounts to nought, because not enough weight on the driving wheels! This also make fast laps harder because it is so easy to spin the car on corner exits.

As I have ranted about for more than a decade now :(, 60%R allows the car to accelerate much faster out of the slower corners. It also makes the car much easier to drive fast. And, as a bonus, you get to win the Acceleration event! :)

But point-mass simulations don't explain this. They simply allow the car to accelerate at whatever rate you have assumed, which is at the edge of whatever "friction ellipse" you have input. And typical bike-engine layouts make 60%R hard to achieve, because big gap between driver's back and forward leaning cylinders, then another gap between output-sprocket and diff.

So most Teams settle for around 50% F:R (the easiest to achieve), and then argue that they have "perfect balance"!
~o0o~

"We also had this idea for a pedalbox..."

Yes, that can work. The main thing is to try to get the front-bulkhead as rearward as possible. So Percy's ~900 mm long legs (check rules?), plus maybe ~100 mm for the pedals, then the front-bulkhead.

As noted by Jan, the MCs-under-floor makes the frame a bit higher, but many cars also run very high footboxes ("Hey, everyone in F1 does it, so it must be good...").

Here is how I would do Better Brakes. (http://www.fsae.com/forums/showthread.php?11873-Vertical-mounted-master-cylinder&p=121539&viewfull=1#post121539) Also more suggestions on the rest of that thread, such as Tokyo Denki's on page 3.
~o0o~

Oh, and don't get too stressed now, with all these different ideas floating around your head. THIS IS THE FUN BIT! :)

Z

mdavis

11-02-2014, 09:44 PM

Mitchell

11-02-2014, 09:57 PM

http://i1296.photobucket.com/albums/ag13/challicm/EDB2D855-7CB8-4FAE-905E-0BCFDD61A2CB_zpsfhwpd73b.jpg[/img]

As Z has mentioned, the bearing fixed to the chassis, and rolls in vertical machined aluminium slot bolted to the beam. This allows the beam to be unrestrained in vertical movement and roll. The monoshock due to the mode separated suspension and isn't particularly important to the constraints on the beam. The same link system would work with a shock at each side of the chassis. Actually it makes it very easy to get the MR you desire by the position of the shock mount on the beam.

Unless you move to hinge type masters that is a great way of packaging your pedal box. If you mount the whole assembly on rails even better.

I will be very suprised if you have a complete car by Feb. We design freeze end of March each year for a complete car in July. This year it blew out til mid september, mainly due to learning some new manufacuring methods and a complete new vehicle concept. Our competition is in December.

Jay Lawrence

11-02-2014, 10:14 PM

On the subject of sumps: a well baffled custom wet-sump can be around 40-50mm thick and doesn't require you to package scavenge pumps and separate oil tanks/lines etc. I know anecdotes are a bit silly but here's one anyway: UoW (CBR600F4, now CBR600RR) went to a dry sump system for 2008. Unlike some people's experience with a first attempt at a dry sump system it worked very well, but when I took over powertrain in 2009 I reverted back to a wet sump. This was partly because I was a bit bewildered by the amount of work ahead of me and partly because I/we couldn't justify keeping the dry sump (higher part count, heavier, extra load on engine to drive pump, packaging issues (significant given our intercooled turbo setup)) over the wet sump (simple and proven concept over many years, albeit with a slight CG hit). Anyway, I guess I'm just saying that the standard sump must go, but that doesn't mean going all the way to a dry sump system (which will take someone fairly dedicated to implement).

MCoach

11-02-2014, 11:35 PM

You could always take your mock up and set it up on two scales and have the driver adjust him/her-self to different seating angles. This will allow you to see in real time the mass distribution change of each style of seating. Mostly what you will see is that as you lay your driver further and further down your weight shifts forward because you can't really move back with an engine in the way. Your driver's cg will also lower considerably. I think for 2014 we were running a seatback angle of 28 degrees from the horizontal (Yes, the ground!). We were certainly the smallest car at the two US competitions, but paid dearly in length due to Percy's massive legs. Just a heads up.

Z, on your point about the front hoop design of most FSAE cars, this odd shape is typically done to pass the vertical template test as there typically isn't an intermediate connection between the roll hoops, so to keep the main hoop from being excessively wide, the front is made wider which drives the top being wide due to the tubes required to attach to them for side impact tubes and the exceptionally large horizontal template that must be passed as well. As much as many teams would like to reduce the size of the front hoops, it's mostly driven by the current template rules.

For some other brake stuff, check out some of my older brake posts, I think I dropped some solid basic info in there.

For the weight balance, it's been argued many times, but there are some other considerations other than "I've been arguing this for decades and no one listens" is that the FSAE market for tires and available sizes is noticeably limited compared to either go kart manufacturers selections or much larger tire sizes. On top of that, the manufacturers and compounds don't mix and match very well throughout the series, so you're pretty much stuck with a few options, most of which have too much mass to try to dump energy into them. Want to use my favorite commercially available compound? Well, it comes in one size, and one size only. Want to move up to the next size? Then it'll be like driving on ice cubes as the tires will never heat up. So, it's not quite like the 80's F1 days where anyone really has the power and weight to put 70% of the weight (or more) on the rear axle and still have tire compounds (and suspension) that will both match correctly in cornering stiffness and roll stiffness with that bias. So something near ~45% Front become a nice happy target to shoot for with equally matched tires all around. Just throwing that out there for everyone, too.

With regard to the high roll centers, you'll want higher roll centers for FSAE than you would want for anything else. How often do circuit cars have to turn there wheels more than 30 degrees? FSAE you might get a few successive turns like that. Too low and your car won't react fast enough, throwing away responsiveness, making it slow. mildly high roll centers in FSAE is like having your cake and eating it too. The soft springs help let the chassis lower the sprung mass during cornering by being softer even though jacking forces are trying to push the car up. So, get it right and the car will play predictably in driving as well.

ChristianChalliner

11-03-2014, 08:49 AM

Jan - Thanks again! You don't have to sugar coat the build quality, we know it's awful and it's one of our big things to improve, the reason it's so bad was because time simply ran out :( For the pedal box reservoirs I was thinking if a banjo was just used to turn the outlet 90 degrees then the reservoirs could be off to the side shrouded by a small plate/floor access 'hump'. I did look into vertical mounted master cylinders too but I think this method has the ability to push the bulkhead even closer to the pedal face.

z - Ahh ok I understand that now :) I did a bit of thinking on the beams (drew a few sketches, going to build a physical model later) and something that seemed to be the case was this:

Beam = best camber control roll/bump, worst in single wheel bump, most un-sprung mass

LLink = worse version of beam (poor camber control in bump) less un-sprung mass, slightly better camber control in one wheel bump (unaffected wheel stays flat)

Swing arms = similar to LLink really, higher RC if parallel to ground.

Double-wish (with average FVSAL lengths) = pretty much the 'jack of all trades master of none' largest number of hardpoints, some (possibly lots) camber deficiency in bump and roll, un-sprung similar to that of LLink but likely the best at dealing with one wheel bump situations.

I guess the interesting point is that, we run on tracks with no kerbs that are completely flat so why do we care about one wheel bump situations at all? and if they do happen they're likely to be infrequent.

So I'm actually leaning towards beam axles... but I do feel like I've been slightly pushed that way, certainly makes rear hardpoints easier.

The idea of a custom casting is something we have thought about and it's possible it will happen in the future depending on if one of our team members gets his placement at the casting company.

I get the 60/40 argument, it's just if we can actually achieve it, we're still trying to shuffle everything as far back as we can get them to go whilst being reasonable.

915mm is the leg length. See the MC's under floor doesn't make the frame higher in my mind, if the MC's are sat just above the lower edge of the frame rail then there only needs to be a slight height increase in the floor above them. If this point is under the bend in the drivers legs then why does it matter that the floor is higher there?

Fun bit?!!!!! It would be fun if I had years to think about it yeah, it's the time issue that makes it substantially less fun!

Matt - Thanks I'll have a look for that and pass it on to the driver environment guy too. Well to be honest 'big picture VD' is effectively my project title but it goes under the guise of 'suspension' here, that's partly due to a lack of understand about the project but I wouldn't like to discuss that any further for obvious reasons.

Mitchell - That makes sense now, I just couldn't see the vertical slot, if we were going down the beam axle route we'd probably have to go with two shocks since I doubt one of our small shocks could take the load on its own. I see what you're saying about the MR too, seems simple enough :) The pedal box will likely be sliding on the frame rails with a simple pin dropping through the pedal box and frame (with a split pin to stop the pin falling out), easy to adjust and simple to make. I too will be surprised but I think it is possible providing everyone really pushes it.

Jay - Interesting thoughts, I'll pass them on to the engine/dry sump guy.

MCoach - Nice idea with the mock up, we actually had a full set of scales but they've just been sent off for repair as the load cell gave up in one of them. I see the benefit with the high roll centers (more kinematic weight transfer = faster than elastic transfer) but how high is really too high? I have no experience of what I'm aiming for here, 50% elastic, 50% kinematic transfer? 90% elastic, 10% kinematic? I have very little reference points to go off, likewise with how much steering lock do I want? All I know is that last year 28 degrees at the outside wheel wasn't enough but how much does that need to increase by to be useful? or was it because of the awful ackerman that made it so clumsy around corners? All questions, all tricky to answer when starting from zero.

---------

Just a quick thought (I have a lecture in a minute) but if I was to go to a front beam axle, where would I mount the steering rack? on the beam seems easy but then it will be rotating and moving WITH the beam, wont this lead to strange steering characteristics?

Thanks all of you for your input, it's really helping us all out here! :)

mech5496

11-03-2014, 10:32 AM

There are also pull-type MC's, we use them since 2010 and work reasonably well...plus being short they are not affected by the footwell template (less than 100mm length). Regarding the steering on the beam argument, take a look at sprint cars and their way of doing things.

MCoach

11-03-2014, 12:15 PM

Christian,

I do not yet have an answer as to how high is too high, however, in layman's terms: the lower limit of 'too high' is where your car is reacting faster than you can keep up, "twitchy, or darty" as it is done with a maneuver before you have time to catch up, the upper limit is where your car rolls over. I wish I had more time to explore the concept and calculations myself, but it's crunch time for me. Adding an extra hole for the control arm to mount to can give you some roll center adjustability which may/may not add value to testing your car.

Steering, you could always use more steering lock. Drift cars have a nice set up for high lock to lock steering. If you're finding that you don't have enough steering lock, you can always add some toe out in the rear. :) ....not that that is a bad thing anyway. It'll help the car yaw more to navigate around tighter corners.

Since I'm actually doing our kinematics this year, I've been designing beyond what the car is 'designed' to roll to just to make sure that what ever compliance from some poorly designed part that pops up won't affect the system a whole lot, so thowing points in areas with low sensitivity to change. On that note, it's really something to watch a car go out on track with -4 degrees of camber....and still watch it at a positive angle in every single corner. It's baffling.

A beam is best for roll control, but that's not to say you can't get similar performance out of a double wishbone. You may end up sacrificing some bump conditions for actually getting accurate control over roll conditions, but I think it sounds worth it. Especially when the god awful camber gain in brake dive everyone complains about can be nearly mitigated through stiffer springs, a heave spring, or some other funny things.

As for your scales, find some mates who have bathroom scales. Amateur hour can still work in these conditions and sometimes a low accuracy tool is better than no tool at all.

Good luck. Hopefully nothing I've said in this thread seems like hearsay.

Luniz

11-03-2014, 02:40 PM

Getting back to the brake MC setup: The configuration you mentioned can be achieved very conveniently with very tiny master cylinders like these for example: http://www.sportsbike.com.au/images/beringer_rear_brake_master.jpg

For comparison: The rod ends are mm if I remember correctly...

ChristianChalliner

11-03-2014, 06:22 PM

Mech (Harry) - I'll have a look, thanks for the tip (on both counts) :)

MCoach - That makes sense to me but seems tricky to quantify without a physical car and roll center adjustment points to see the back to back effects. Steering, yep I agree, providing that your arm angles aren't limiting your steering lock! :p I understand the compliance factoring (or at least I think I do) but it's something easier quantified with physical testing to my mind.

I can't say I agree with you on running stiffer springs to counter the dive/traction effects because if I understand it correctly you're crippling your performance in traction zones to do it. Bathroom scales is an option, we did actually talk about that.

Doesn't sound like hearsay to me but then again I don't know much!

Luniz - That looks interesting, I'm assuming you were going to say 8 or 6mm? we are looking at getting new master cylinders since our current ones are not spherical mounted at their ends, what kind of prices are we talking?

Onto my next thing, I get the impression I'm going to make myself look rather stupid over the next few sentences but here goes!

(I assume all camber increases to mean negative camber gains!)

With a double-wish with FVSAL's bigger than track/2 camber compensation in roll is sub 100%, now to my mind, any steer input will impart a roll event so the camber winds off as that begins, turning the wheel (assuming some caster angle) will increase the camber again so the camber is roughly increased back to its original static setting (or more, whatever you fancy!) but the caster gives you a jacking effect which is bad as it moves the CofG higher correct?

So... with a beam axle, there is no camber change in roll so there's no need to dynamically add camber to the system so why run any caster at all? if you want some steering 'weight' (again another topic on how much is enough/too much/etc) and self centering just add some mechanical trail (with spindle offset). With no caster there will be no jacking so no ill effects... seems a bit have your cake and eat it but what do you guys think?

(Note I have assumed the tyre doesn't pull under and reduce its own effective camber angle which I understand to be something quite possible?, I have also assumed infinite stiffness uprights and beams which again are likely not true).

I'd also like to add that we have a 2D plasma cutter at our disposal so I'm going to draw up some 1/2 scale beams tonight and hopefully cut and get them welded tomorrow, I do much better with proper visual aids than CAD/theory so I think this will help me, plus it will give me an idea of how long it takes to make the beams.

For a beam I was thinking of going for a inverted Watt's linkage (center on the frame, pickups on the beam) for starters as RCVD talks about peg and slot designs being tricky so for a starter I'm going to try Watt's link. I'm still struggling on how I would package a front beam but I'm thinking 4 arms leading to the front bulkhead?! not sure how I'd constrain lateral motion though and I still don't have the steering issue figured out but I'll get there!

More sketches tomorrow! (sorry I never got round to posting a new one yesterday)

Jan_Dressler

11-03-2014, 07:13 PM

On the subject of sumps: a well baffled custom wet-sump can be around 40-50mm thick
12.5 for my old team's last dry sump, without modifying anything of the engine crankcase ;)

extra load on engine to drive pump
But then again, you will get some power back (crankcase vacuuming)...

Jay is of course correct with the rest of what he said, dry sump does mean extra issues, he does mention a few.
On the other hand, it will also take someone fairly dedicated to develop well enough baffles (or rotary/swinging pickups, or whatever) that actually work good enough on a shallow sump, without "overfilling" the engine with oil. I have seen at least as many teams which destroyed their engines with poorly (or overly ambitious) designed baffled sumps than with dry sumps.

Well, you have to weigh the arguments for yourself :) Both options have their pros and cons.

Jay Lawrence

11-03-2014, 09:45 PM

Jan,

I think our dry sump was a similar thickness, but at the time we were running a CBR600F4 and the shifter lever had to point downwards. We were running a single gear at the time so not having a shift lever didn't matter (otherwise the shift lever would have gone below the chassis...). Something to possibly be aware of, but I think the geometry of the RR engine negates this anyway.

And yes, don't underestimate the complexities of either system. Another anecdote: after I left the team there was a wet sump 'design' that didn't have baffles at all. The solution? "Just add more oil." I think it ended up with something like 6 litres in there to stop it surging. It ran just fine, but was certainly not desirable.

11-03-2014, 10:14 PM

Christian,

TIMELINE - Given that you have to the end of this month (say?) before "final concept" is frozen, it is good that you are investigating all these different possibilities now. The final concept drawings are only hand sketches, or maybe even just your tapelines-on-floor, so they only have to be "frozen" on Sunday night, 30th November.

On Monday 1st December, you have a big Team meeting and say, "These are the major dimensions. Now let's get detail drawings finished before Xmas...". Or something like that... :)
~o0o~

SUMP - Preferable is lower engine CG via a shallow sump, either dry or baffled-wet.

But ABSOLUTELY ESSENTIAL is an engine that works reliably.

So maybe set your overall concept dimensions based on a lowered engine fitting in a minimum wheelbase chassis. Then, worst case, if this engine is not ready for early testing, you fit your regular engine a bit further back, which probably means stretching the wheelbase to 1.6 m (or even 1.7 m?), and fit wheelspacers to widen the rear-track a bit.

The higher CG will still allow the car to accelerate hard (ie. more rear weight transfer). The longer wheelbase and wider track will slightly slow-down lap times. But lots of driver testing will speed-up lap times much more. Then maybe in May (???) the lowered engine is ready, and you can go back to the shorter and narrower car. Wow, faster still...

Expect to take quite a few of these detours. Nothing much is linear in the real world...
~o0o~

CAMBER CONTROL - "Beam = best camber control roll/bump, worst in single wheel bump, most un-sprung mass."

NOooooo!!! This very common mistake comes from a complete lack of clear definitions, or clear statements of assumptions, that is all too typical today (ie. failed education system...).

Namely, what is a "single wheel bump"???

I covered this before, so won't go into detail again. But any passive suspension has ABSOLUTELY NO CONTROL of the "camber change" that comes from short wavelength bumps. (And a possible good definition of a "single wheel bump" is one that "has a wavelength less than the distance between nearest wheels".)

Anyway, think about the relative front-view angle between the undistorted tyre-footprint and the road-surface as a car drives over a very heavily rutted road. This angle is constantly changing from +~45 to -~45 degrees, regardless of wheel-camber wrt chassis.

For FS purposes, the road surface can be considered a straight-line passing through the two tyreprints (ie. only VERY long wavelength bumps). So, whenever one or both wheels move up or down, the best camber control comes from a beam-axle. On this flat road, there are ALWAYS situations where independent suspensions give "bad" camber.

Yes, the beam does have a bit more unsprung mass. But see the last few pages of the "Beam-Axles..." thread for Ralph's pics and links to beam-axled cars racing on what amount to ploughed paddocks. And quite fast they are...

For reference, the "best" suspension kinematics for off-road racing (IMO, and seen in practice) is NO LATERAL-SCRUB of the wheelprint (ie. so horizontal n-lines, or ground level "RCs"), and NO CAMBER-CHANGE (ie. infinite FVSALs, for minimum gyroscopic forces). These kinematics are easiest achieved with pure Leading-or-Trailing-Arms (ie. a lateral-pivot-axis swing-arm).
~o0o~

ROLL-CENTRE HEIGHTS - Warning!!! Alarm bells!!!!!

DO NOT HAVE "HIGH" RCs WITH INDEPENDENT SUSPENSION!!!!!!

Well, you can, but if you do, then you MUST take appropriate measures.

For example, fit a stiff anti-droop mechanism to the Axle-Bounce-mode (eg. use a "droop-limited third-spring"). Or just use the standard solution when people back themselves into this corner, and fit really stiff springs everywhere, so as to prevent any suspension movement at all. "Any suspension will work, if you don't let it..."

"High RC" in FS conditions (ie. track ~1.2 m) is anything above about ~0.1 m. That gives a Jacking-Force ~1/6 x the horizontal-cornering-force, which can start to give significant chassis lift. Then bad things happen... As noted above, there are ways to cope with this, but please be aware of the potential pitfalls first.

Also note that Beam-Axles DO NOT JACK. Well, not in the same way. So you can run highish RCs with beams. On rough tracks, lower RCs are usually better (see "lateral scrub", last paragraph, last section). On FS type tracks, and with beams, you could have the RC at CG height, with very soft springs all around, and no body roll through corners. Of course, then all LLTD tuning would have to come through F:R RC height. Easiest to start with RC-height at a convenient 5 - 10 cm.
~o0o~

BRAKE-PEDALS - I think there are enough "prior art" solutions out there that, at the big-picture level, you can consider the front-bulkhead to be just in front of the forward-most pedal position (= Percy's 915 mm legs).

Design guidelines for Brake-Guy:

* The brakes MUST be able to lock all four wheels at Scrutineering.

* They SHOULD have a "hard" pedal, and an easy-to-modulate feel.

* They DO NOT have to be "optimised" to the N'th degree. (An excess kilo or two will NOT make any measurable difference to lap times.)
~o0o~

I better get going on these Beam-Axle sketches. (Steering can be done via a telescopic, ball-bearing-splined shaft, to be shown on sketch...)

But meanwhile, make sure you get lots of good sleep now. Your brain does its best big-picture thinking then. Well, mine does... :)

Z

MCoach

11-04-2014, 12:40 AM

Only thing I really have to add at this point is that Z's definition of 'high' roll centers is higher than what I was considering high.
I was considering a high roll center to be anything really above about .75m so I guess Z has a higher limit on jacking forces than I was considering.

Mitchell

11-04-2014, 10:46 AM

While I believe a beam axle rear is a fantastic solution for fsae I am not really sold on beam axle fronts. We completed a design with a front beam axle but scrapped it due to many issues.

The whole nose of the car needs to be higher: 20-30mm beam clearance to ground + ~60mm high beam + 30-40mm clearance to chassis for suspension travel and you are looking at the chassis floor starting 100mm off the ground. Add in template height and a top to the chassis and you can't lie the driver down anymore because they can't see over it all.

The chassis structure gets messier: to get the driver low and the nose high (for beam clearance) you have to have either a large step up in the chassis or lift the driver, can't have a flat floor (at least with a 4cyl).

The steering system is significantly more complicated and has more sources of compliance/play. With double wishbone you can easily run a straight shaft from wheel to steering box. No unis, no bevel gears, no special slip joints or bearings. It's cheap, effective, light and has little play. If you're smart about it you can even have good ergonomics. Steering lock with a beam was also more difficult to achieve with the trailing arms required for longitudinal control. Finally with steering, due to the low mounted steering box, low clearance to chassis/steering link in roll and packaging a steering pickup in 13" wheels - the angle of the steering links becomes quite steep in front view, creating bending loads in the rack. Hello compliance.

The front of the car already has a pretty great structure to bolt some wishbones to. A rear beam removes a large amount of unnecessary chassis structure, the front does not. I am sure with more effort these issues can be solved. The ECU steering solution is a great start and i wish I had thought of it, although we still probably would have ended up with a wishbone front.

ChristianChalliner

11-04-2014, 11:12 AM

Z - Single wheel bump would be a fairly major road anomaly (pothole) I suppose or a kerb, neither of which exist in FSAE.

In other terms, I think the idea of having major design work only starting in December is far too ambitious, you assume people are like robots and will work on concepts day in day out and lets be honest people are just lazy and wont do that!

One thing I did read which leaves me at somewhat of an issue is that RCVD says that the RC isn't completely linked to the kinematic and elastic weight transfer distribution in the case of a beam axle, in which case how does one determine the split and its relationship to the linkages used?

With regards to tips on the braking system, It's fair to say it's most likely going to be me spec'ing everything about them, our calipers are fixed as the current AP Racing 4 pots (too expensive to change) (also thanks BCU for lending them to us!) but master cylinder sizing, etc is up in the air.

Anyway, onto sketches and a few ideas!

WB=1530mm
CG height (with current engine spec) = 297mm
CG height (with dry sump) ~ 250mm
F/R WD = 35/65
Ground clearance = 30mm

Basically the big square is the engine and the crossed square represents the size of our current diff sprocket, biggest circles are wheels, I've also included percy along with arms to get a feel of the steering reach required. Furthest forward point is the bulkhead/IA plate, next up is pedal face, etc (big cross line represents top of side impact structure).

http://i1296.photobucket.com/albums/ag13/challicm/Draft_zps8edb4d58.png

Main assumptions are that the two largest masses drive the WD (driver + engine) I appreciate this will change substantially once the other parts are added in but that will probably move it forward 5% or so (I've also just realised the drivers CofG is probably slightly further forward given the leg position but I'll rectify that on MK2.

Slightly disappointed no one had anything to say about my thoughts on caster and hanging suspension hardpoints from the IA bulkhead :p

11-04-2014, 08:09 PM

Christian,

Very briefly today...

* Yes, no "bumpy tracks" in FS. For "kinematic camber changes" it is enough to think of the wheels sitting "stationary" on a flat road, and the car-body moving in heave, pitch, and roll.

* I was suggesting that the early stages of design, say November, are very "fluid", with lots of free-hand sketches (like your underfloor-MC brakes <- good!) but not much accurate dimensioning. Then later, say December, each team member starts "filling in the details".

* Beam and independent suspensions are very simple mechanisms. They are best understood using the age-old principles of Classical Mechanics (= Statics + Kinematics + Dynamics). Anything you read in modern, dedicated "VD" books should be taken with a very large grain of salt. (More detailed explanations later, if you want...)

* Yes, driver's CG is forward/above their navel/belt-buckle. Quite heavy IA/front-bulkhead, which is long way in front of front-axle also makes a difference (because nothing similar behind rear-axle). Also here I would suggest fitting the radiator just behind the engine. This "close-coupling" simplifies plumbing and allows thermosiphon.

* Keep in mind that a lowered engine will allow you to shorten the car. But at the moment you are at the minimum limit... So, perhaps, move front-wheels 100 mm forward relative to driver and Front-Bulkhead, for wheelbase = 1630 mm. Then if you manage to lower the engine you can push it and the rear-wheels forward to get back to the minimum wheelbase again.

* Castor, BY ITSELF (and with narrowish tyres), DOES NOT JACK (err..., not much, and depends on wheel radius...).
Castor + Offset DOES JACK, potentially quite a lot!
Big subject, better left til later, because not important now. (However, if a Team intended to run a spool-diff, then this would be important to think about now.)

* Yes, IA/Front-Bulkhead is a VERY GOOD PLACE to hang suspension from! Unfortunately, most Teams have their IA/FB waaay too far forward, because of failure of good thinking at this big-picture level.

Z

ChristianChalliner

11-05-2014, 05:21 PM

Sketches - That's possible but I don't trust people enough to let them design nothing until December as currently a lot of people have come back with nothing, hence why I was drawing the pedal box ideas.

Beams - True, they are at least much simpler to analyse in terms of forces than the double wishbones but with the exception of panhard bar constrained setups I'm struggling to understand where the location of the RC actually is but I'll keep going and see where I get first. More detailed explanations would be nice but I will try myself first and post the results :)

Radiator - Difficult for now, personally placing it on the car centerline seems a good idea for L/R WD but unless it was to sit behind our diff it might be difficult to do that. Currently it sits on the left with the exhaust on the right but I think the radiator when full is probably heavier (but I will weigh it and see)

Castor - I think I understand somewhat... would I be on the right track to think it causes an inside rear wheel to lift? (Quite prepared to be told I'm wrong!)

Well, I think it's possible to do, our tape mockup went well although some members were in dis-belief at how short the car could actually be! We're going to make a wooden mockup tomorrow so I'll post pictures once we've done that. I also started messing around with designs for the beams, actually a bit trickier than I thought but again, once I have pictures (especially of front steering) I will post them, looks like an R&P makes life more difficult than necessary though...

Jay Lawrence

11-05-2014, 10:02 PM

Christian,

The side pod is the go-to place to mount your engine heat exchanger. It balances the exhaust out (like you've mentioned) and can keep your yaw inertia (and CG) down. Just don't try to get fancy with 'optimising' your sidepod design. A big opening with a well sealed fan on the back is a good way to go.

As for castor, take a look at a go-kart. Turn the steering hard one way and feel what happens to the inside rear wheel, remembering that karts have spools.

mech5496

11-06-2014, 04:45 AM

Christian, I regarding RC's I would really suggest to take a look at Z's posts regarding n-lines, they will help you understand a TON about linkages in general.

Menisk

11-06-2014, 09:33 AM

* Yes, IA/Front-Bulkhead is a VERY GOOD PLACE to hang suspension from! Unfortunately, most Teams have their IA/FB waaay too far forward, because of failure of good thinking at this big-picture level.
Z

I don't think it's a failure of big picture thinking. I think it's more the pesky problem of drivers and percy having legs. Ultimately your rear wheels end up as far forward as your engine and driveline packaging will allow, you place your driver as close to the engine as you can and your front bulkhead gets defined by leg length of your ergo. Unless you want to extend your wheelbase beyond the minimum defined, but that's going to hurt you on our tracks. Ultimately we attempt to get everything in the car as close the rear wheels as possible and the front draws itself based on the position of the driver and his seating angle.

MCoach

11-06-2014, 12:54 PM

11-06-2014, 07:44 PM

Menisk

11-06-2014, 11:05 PM

Groooaaann..., excuses, excuses... :(

Minimum wheelbase,
+ very low CG,
+ very low Yaw MoI,
+ best F:R% for RWD (~40:60+),
+ driver's CG close to car CG (for consistent F:R%, and implying driver entirely WITHIN wheelbase),
+ narrow fuselage for good aeroflows,
are ALL possible, and all VERY EASY, because...
= BROWN GO-KART!!!!!

Doing this simply requires you to STOP COPYING EACH OTHER, and START THINKING BIG-PICTURE!

(Hint (for thousandth time...): The engine-drivetrain is merely "the necessary ballast". As such, it can be squashed into whatever shape best suits the overall plan. And since the rest of the car is SO SIMPLE to build (remember, "brown go-kart"!!!), there is plenty of time and resources available to squash the engine-drivetrain into whatever shape you want.)

Stop copying everyone else, stop being so lazy, and DO SOME ENGINEERING!

... like trying to put brains into statues... :(

Z

Very low CG means lying your driver (the heaviest component of your car) flat, which means his heavy legs stick out forward, increasing your yaw inertia. This also moves your bulkhead forward, so if you want him entirely within the wheelbase, you're not going to have a minimum wheelbase. From the sole of my foot to the back of my bum is 1100mm while I'm sitting bolt upright. No one sits bolt upright is an SAE car because you raise the CG way too high. You're asking a lot to fit the driver entirely within the wheelbase and be minimum wheelbase as the driveline and CV angles limit the location of your rear axle. Literally the only way to achieve that is to turn the engine around a have a mid driveline and dangle the engine off the back, something interesting I'd like to have a look at.

Also last time I check engines aren't squishy. They're pretty damn rigid and the have a set size. You cram everything as tight as you can to it but you can't just magically make the gearbox disappear and the engine shorten. I'm sure with a single you can probably achieve a 40:60 bias with the conventional layout of driveline behind engine, but no chance with an inline 4 with low CG. With a single you're not going to have to worry about putting power down, you don't have any (not necessarily a problem). At this point the rear weight is only good for evening out wheel loads under braking. Long and short of it is you can't have all the things you want. They're all trade offs.

I can only assume your legs must end at the knee, the rest of us have to deal with the problems normal legs cause. Please stop chanting that people are mindless idiots on this forum. There are annoying realities caused by rules and the physical size of drivers that you completely ignore.

mdavis

11-06-2014, 11:23 PM

Typically at these levels, Rear axle center line is defined by how far forward the differential can be placed without becoming a sawblade applied to engine. The front is defined by whatever it takes to reach the desired F/R weight balance. This implies that as much weight as possible is already shoved to the back, allowing the car to achieve close to the minimum wheelbase with the desired balance.

The way we did it was start with the rear wheels/tires in a spot, the place the diff as far behind as we were willing to. From there, but the engine against the diff (as close as possible). Then place driver. This starts by moving everything as far back as possible, where your method could have the diff pretty far in front of the rear wheel centerline, which moves CG forward. We ended up something like 45-46% front with 160lb driver.

Groooaaann..., excuses, excuses... :(

Minimum wheelbase,
+ very low CG,
+ very low Yaw MoI,
+ best F:R% for RWD (~40:60+),
+ driver's CG close to car CG (for consistent F:R%, and implying driver entirely WITHIN wheelbase),
+ narrow fuselage for good aeroflows,
are ALL possible, and all VERY EASY, because...
= BROWN GO-KART!!!!!

Doing this simply requires you to STOP COPYING EACH OTHER, and START THINKING BIG-PICTURE!

(Hint (for thousandth time...): The engine-drivetrain is merely "the necessary ballast". As such, it can be squashed into whatever shape best suits the overall plan. And since the rest of the car is SO SIMPLE to build (remember, "brown go-kart"!!!), there is plenty of time and resources available to squash the engine-drivetrain into whatever shape you want.)

Z

I don't think any of the current popular engine setups are going to give this result. Do I think it's possible to put together a brown go-kart? Yes. With the current popular line of thinking? Probably not. Newer Yamaha dirt bike engine would give the best bet (rearward tilted cylinder) of the currently used options, but I still don't think it's enough. Someone is going to have to think outside the box to get this to happen, if they really want to do it, unfortunately. ETS is probably the closest to this package, but they still have a lot of unnecessary bits on the car.

From some layouts I did, I think a 72" wheelbase would be about perfect to have suspension points hanging on the front bulkhead with a much more traditional rear end layout (4 cylinder, chain drive, nearly straight halfshafts, etc.) and provide 60+% rear weight bias. This would be a really fun A-Modified project for SCCA autocross, if I had someone to bank roll it, and could drive at a level to do the car justice.

-Matt

Mumpitz

11-07-2014, 10:09 AM

bonus points for Jawa content

http://www.thumpertalk.com/topic/1010427-home-built-exhaust-not-a-motorcycle-but-surely-a-thumper/

MCoach

11-07-2014, 02:54 PM

Matt,

My assumption is that the differential is never in front of the axle centerline which basically leads us to the same conclusion.

However, this should not be the focus of this thread, and not really Jawa motors either. This should be dedicated to entertaining the questions and progress of "vehicle dynamics starting points and design process" and not allowed to be spiraled into another bitch and moan thread about everyone's an idiot. Let's stay on track and encourage our newcomer along his objective process of designing and building this thing.

Christian,

I see you have your desired weight balance and some other parameters posted. While these are considered achievable, you can make a spreadsheet to track as much of the heavy items in the car as you can, (Engine, Driver, Tires, Wheels, Steering Rack, Bodywork, Chassis, Differential, etc) so that you can easily track your MoI, overall CG relative to wheelbase, and make decisions on discrete placement of packaging items beyond "hm, well, this 12lb battery fits nicely right here on the front bulkhead, ol' chap".

This can help with the accuracy of your calculations compared to what you actually build.

ChristianChalliner

11-07-2014, 06:11 PM

Just a quick note from me (Too tired to write something in full now, that will come tomorrow).

Thanks MCoach for saying pretty much what I was going to say (and also giving me a good laugh with the battery comment!). I have no idea why the Jawa is relevant here and I don't wish for this to turn into another argument like most threads on here.

I have made a CofG spreadsheet though and I'm currently weighing all our fixed components to get an idea of F/R WD and CofG height. We also made the trip over to our neighbors Birmingham City University today (we are literally across the road from each other) really good people and had a great chat about things :)

EDIT: I did also try to change the title of this thread to "Aston University Design and Build Thread" or something similar but it doesn't appear to have worked.

11-07-2014, 11:27 PM

Christian,

I am going to digress from the topic of "Aston University Design and Build Thread", but I am sticking firmly to the topic of "Vehicle Dynamics Starting Points and Design Process". I will try to keep this digression to just this post.

I am doing this because of the huge resistance there still is here to any serious consideration of these "Starting-Points/Big-Picture" issues. Despite the importance of these issues being repeatedly discussed since this Forum began about twelve years ago, and despite Geoff putting in a mountain of work with his "Reasoning..." thread of over five years ago, by far the majority of Teams still TOTALLY IGNORE THIS "BIG-PICTURE". Worse yet, some actively fight against it (see below).

Much of the problem comes from the Team Supervisors, such as yours, who lock their Teams into an ineffective design by mandating the engine-type and wheel-sizes. There is not much you can do about this, but other Teams do have the option to move to better designs. They just have to have the big-picture issues explained to them. Again..., and again..., and again...
~~~o0o~~~

So, as a reminder to other Teams out there, here are the most important VD features that a good FS car should have, IMO.

Minimum wheelbase,
+ very low CG,
+ very low Yaw MoI,
+ best F:R% for RWD (~40:60+),
+ driver's CG close to car CG (for consistent F:R%, and implying driver entirely WITHIN wheelbase),
+ narrow fuselage for good aeroflows,...

And, once those are in place, the biggie to add is a shed-load of aero-downforce (ie. add mega-AD to above VD).

To restress this, these Overall-Size and Overall-Mass-Distribution issues are MUCH, MUCH more important to having a fast car than all the fussy little Suspension-Kinematic, and Spring-Damper-Rates, and whatever else..., little details that most Teams spend most of their time on. As noted before, cars have won FS/FSAE with effectively NO suspension movement at all. All those little details amount to squat.

Get these big-picture issues right first, then develop faster drivers, and BETTER AERO.
~~~o0o~~~

Whether you students realise it or not, the main thing preventing you from achieving the above big-picture goals is a deeply ingrained, and utterly irrational, belief that you MUST use engines taken from motorbikes. That is, ONLY engines from 600 cc four-cylinder sportsbikes, or 450 cc single MotoXers, or something very similar, seem to be considered OK. Well, there are a few exceptions (see below), but VERY FEW.

This irrationality is then supported by a never-ending stream of DEFEATIST arguments, such as Menisk's below.

"Very low CG means lying your driver (the heaviest component of your car) flat,...
... so ... you're not going to have a minimum wheelbase. ...
...You're asking a lot to fit the driver entirely within the wheelbase and be minimum wheelbase ...
... Literally the only way to achieve that is to turn the engine around a have a mid driveline and dangle the engine off the back...
... Also last time I check engines aren't squishy. They ... have a set size...
... you can't just magically make the gearbox disappear and the engine shorten...
... a 40:60 bias ... no chance with an inline 4 with low CG...
... With a single you're not going to have to worry about putting power down, you don't have any...
... Long and short of it is you can't have all the things you want. They're all trade offs.
...
... Please stop chanting that people are mindless idiots on this forum. There are [B]annoying realities ... that you completely ignore."

Contrary to "ignoring the realities", I thought through all these issues when I first became aware of FSAE back in the 1990s. The "realities" are very simple and straightforward, and my thinking on them has not changed in 20 odd years. Specifically:

The Rules regarding driver position, foot-box size, mandatory steering-wheel, and FRH above steering-wheel, all mean that a driver "lying flat" cannot see where he is going. So pointless. But lifting the driver's head high enough that he can see over the lowest legal and practical FRH means his head-rest can be less than 1.4 metres behind the pedals. This comfortably fits the driver entirely within the wheelbase!

Furthermore, the driver's raised head and shoulders give plenty of room for an engine and driveline ALSO entirely within the wheelbase. Namely, tucked under the driver's back.

The flaw in the usual student reasoning, as above, is the sub-conscious ASSUMPTION that said engine-driveline MUST come from a motorbike, and it MUST be mounted as in the motorbike, with its chain-drive going back to the diff-sprocket.
~~~o0o~~~

The quick dismissal of the Jawa in some posts above is an indication of just how strong this irrational thinking is.

Briefly, for those interested, a standard Jawa puts out more horses than the standard 450-singles. The Jawa is widely available all around the world. Jawa also make a neat, and separate, two-speed-gearbox, which is useful for different packaging options. And two speeds is enough at these power levels. (I suggest reverse-rotating-crank layout, head pointing to rear, and modified 2-speed-g'box integrated with diff.)

And again, for the record, air-cooled 450 cc turboed "singles" were putting out ~125 hp over 40 years ago. The limit through the FS restrictor is ~120 hp. So MAXIMUM POWER IS POSSIBLE FROM A COMPACT SINGLE! (This is another area where many lazy and "mindless" students were arguing that "it's all too hard, ... impossible...", until I spent 5 minutes finding the countless web-sites that show that this is all, indeed, very possible! Use Search!)
~~~o0o~~~

And there is the "Scat-Single" that I suggested recently. This would require making engine-cases, and possibly a crank, although a pre-existing crank could be used. With moderate boosting 100+ hp would be possible. At these power levels only one gear is needed, though a Jawa-style box could be used. Or a CVT. Or a IVT. Or a regular, small car, auto-box type torque-convertor, preferably with lock-up, but only single-speed. All this could be comfortably fitted, with the driver, entirely within the wheelbase.

The "extra work" required for these types of engines is little more than that usually done on many FS engines, with their intakes, exhausts, dry-sumps, and all the EFI stuff. Given that many Teams are now on their Nn-th iteration of billet-machined-uprights, none of which are any better than the folded-sheet-steel ones they built Nn+ years ago, imagine how far down the track to an ultimate FS-engine those Teams could be now if they decided to do billet-machined engine-cases instead!

It is quite bizarre that in this engineering competition there are so many student engineers who are so averse to engineering an engine!
~~~o0o~~~

Perhaps even more troubling is that even when some Teams are presented with a golden opportunity to do some of the above, they IGNORE THE BIG-PICTURE issues.

So, take for example RMIT at Oz-2013, who ran the Yamaha "Genesis" 500 cc engine. This is a vertical, parallel-twin engine, coming standard WITHOUT a gearbox. (IIRC, it is meant for snowmobiles, with CVT drive as standard? Corrections welcome.)

Anyway, a perfect opportunity to really squash the car up, as explained above. But the driver was sat in the same place as all standard cars! Namely, with knees over the front-axle. Then there was a significant gap behind the fire-wall back to the engine. Then another gap back to a bespoke 6-speed sequential gearbox. (Why 6-speed!? And why the really stupid carbonfibre case!!!?) Then another long gap back to the chain-driven diff.

In short, a great opportunity wasted, because NO THINKING at this important "VD-Starting-Points..." level.

Someone..., some day..., please..... :)

Z

(Edit: Here is another car with the Genesis/Phazer engine. Is all that space between engine and diff really necessary? Or is it there "...because that's how everyone else does it"?)
http://imageshack.us/a/img580/5782/img20130414121414.jpg

Menisk

11-08-2014, 07:05 AM

The Rules regarding driver position, foot-box size, mandatory steering-wheel, and FRH above steering-wheel, all mean that a driver "lying flat" cannot see where he is going. So pointless. But lifting the driver's head high enough that he can see over the lowest legal and practical FRH means his head-rest can be less than 1.4 metres behind the pedals. This comfortably fits the driver entirely within the wheelbase!

Have you ever driven one of these car's Z? We have a 30 degree seating angle this year and you have plenty of visibility forward. You only need to see the top of the cone looking forward, the majority of your vision requirement is the front wheels so you can place them as close to the cones as possible. You can seat the driver nice and upright too, but he is the heaviest component and you're now contradicting your low CG requirement. Also how the heck do you expect to have your rear axle 125mm behind the headrest without an unachievable amount of driveshaft angle. I don't know what shape engines are in your part of the country, but motorcycle engine or not you're going to have trouble squeezing anything bigger than a 100cc kart engine behind a driver and have the driveline somewhere the allows the rear axle to be 125mm behind your headrest.

There are ways you could do it. You can have the fun of turning the engine around and running a mid driveline and working out an intermediate shaft to get some form of drive to it from your gearbox output. You could try and turn a single sideways and make a small transaxle for it to a mid driveline. But teams already struggle to get conventional cars with more simple setups built in a year. Who do you expect is building these cars? Fully qualified, full time engineers? Our team's philosophy is the simplest solution with the fewest parts because 9 times out of 10 it's the lightest and most reliable solution.

The "extra work" required for these types of engines is little more than that usually done on many FS engines, with their intakes, exhausts, dry-sumps, and all the EFI stuff. Given that many Teams are now on their Nn-th iteration of billet-machined-uprights, none of which are any better than the folded-sheet-steel ones they built Nn+ years ago, imagine how far down the track to an ultimate FS-engine those Teams could be now if they decided to do billet-machined engine-cases instead!

It is quite bizarre that in this engineering competition there are so many student engineers who are so averse to engineering an engine!

Have you ever built one of these cars Z? Let alone while also trying to study an engineering degree that already has most students forgoing sleep to complete assessment while doing it? There is a reason it costs Honda millions of dollars to have full time engineers design and build engines. To think that some sleep deprived student is going to be able to tear an engine apart to do work with internal mods, cranks, gearboxes etc. and end up with a better package that's lighter than what the motorcycle manufacturers produce is stupid. On top of that they still have to sort out an intake and exhaust and sump solution to suit their car and keep from starving engines of oil. Sorting out a good, efficient and driveable fuel map in itself takes days of time on an engine dyno. I'm lucky enough to have worked with a man that's being doing it for 40 years. To sort out all the setup, track down a few niggling issues and get the fuel and ignition map where we wanted it took 24 hours of engine dyno time. Not all teams are even lucky enough to have access to an engine dyno.

I don't disagree with you that gearboxes are unnecessary in this competition with a 600. We drive our car in 2nd gear everywhere. 2nd gear tops out at 105 and will happily light the rear wheels up at 20km/h. The problem is that engines capable of decent power without a gearbox - like a Yamaha Fazer - are not easy to come by in some places. Apparently when you live in a country that's filled with desert snow mobiles aren't so popular. Motorcycles however are.

This irrationality is then supported by a never-ending stream of DEFEATIST arguments, such as Menisk's below.

Not defeatist, realist. Have you ever built one of these cars? Have you ever built one with a team of student engineers? You've probably built things, how did your first attempt turn out? The key word is student. Engineering students already have a massive university load, and on top of this most need to work in order to feed and house themselves AND build an FSAE car. Most of these students have never built anything close to the complexity of a car and we need to learn all the manufacturing processes at the same time. Yet somehow you seem to think that doing all sorts of crazy engine work that students don't yet fully understand is perfectly achievable on top of the usual intake, exhaust, sump and EFI that we all have to do to begin with. We're students for a reason. We don't know how to do this stuff yet. Clearly we're all stupid and defeatist for choosing a cheap, available and reliable engine package to save resources and minimise the chance of engine trouble ruining the competition we've spent all year preparing for. Not to mention you somehow seem to think you can do all this to have an engine the size of an RC car motor and a driveline packaged under a driver to allow your rear axle to be 100mm behind the headrest. Also, for the record in choosing our engine package we didn't just assume it had to be a motorcycle engine. We looked at everything from snowmobiles and ATVs to microlight aircraft. Motorcycle engines are simply the most practical and affordable option.

So yes Z, you are ignoring realities. So I'll ask again? Have you ever built or driven one of these cars? How well did you first backyard project work? I would love for you to draw me some pictures (with dimensions) of how you intend to fit a 95 percentile driver within the wheelbase of a car and not have insane amounts of CG height. After that you should get out into your shed and build it, and then come beat us all at competition. Until then learn to encourage students without reminding them how stupid you think they are and how superior you think you are. You need to learn how to play nice with others.

tromoly

11-08-2014, 02:20 PM

(Edit: Here is another car with the Genesis/Phazer engine. Is all that space between engine and diff really necessary? Or is it there "...because that's how everyone else does it"?)

Z,

That's my picture, the short answer is the space is needed to make everything fit, also that was the first year we used that engine so there were some uncertainties regarding center-to-center from engine PTO to secondary shaft, so this was left "stock", the next year pulled an inch or so out of the center distance and it worked alright. You do point out the second-biggest issue I have with using a CVT, having to use a secondary shaft increases the rear length of the chassis quite a bit, if a single-cylinder gearbox engine were used atleast 6-8+ inches of chassis could be eliminated.

In addition, IIRC the Phazer twin weighs about the same as a single-cylinder with gearbox, once the CVT pulleys and secondary are added onto the Phazer weight it's already quite a bit heavier and, I suspect, has quite a bit more rotational inertia.

So to answer your question, about 90% of that space is needed for everything to fit.

ChristianChalliner

11-08-2014, 07:59 PM

Ok, so my thoughts (very basic but time is limited again),

I disagree that fitting the driver inside the wheelbase isn't possible, I think it is but that it does require a relatively small engine or extreme angling of driveshafts to do it. MCoach makes an interesting point in having the driver and percy sit differently in the car which is pretty much exactly how I put the basic sketch together, the driver would sit laid down but percy sat relatively upright, meaning that a 'real' driver sits with legs bent in the car and with the bulkhead moved much closer to the driver. We were also considering UJ'd half shafts as opposed to the current tripods we use, we think we can have the UJ's at greater angles and push the diff even further back but we'll see...

I agree with Z that putting the driver flat makes it impossible to see out (something we confirmed with our very basic cardboard 'screen' setup for a front roll bar to see how high was too high).

I agree with Menisk that it is quite difficult to find the time to actually work on very elaborate solutions whilst still working on other projects/coursework/etc.

I completely agree with the steel vs alloy upright issue Z raised, in fact, we dug out some of our old steel ones and commented on how light they were for their stiffness, so much so that it's something we've already committed to this year. Here's a picture of one of our old ones:

http://i1296.photobucket.com/albums/ag13/challicm/7986AE7E-3D79-4FE1-A842-3CD49165C476_zpsj1ntfcbz.jpg

Not the best in terms of neatness (or design) but these are easily lighter than our alloy ones from last year and don't have the rigidity of a wet towel either.

MCoach

11-09-2014, 09:43 AM

Christian,

I've sent you a PM.

Forbes

11-09-2014, 02:36 PM

Christian,

NASA (USA's Space group) put together mass/inertia data for each major component of a human being. They published this information (I do not recall where, one of my team members found it in 2013) somewhere online, and that allowed us to look at seat back angle vs. CG height vs. Yaw Inertia for various seat back angles.

-Matt

mdavis, Christian

I believe this is the link to the NASA document: http://msis.jsc.nasa.gov/sections/section03.htm#_3.2_GENERAL_ANTHROPOMETRICS

Forbes

11-09-2014, 10:01 PM

So yes Z, you are ignoring realities. So I'll ask again? Have you ever built or driven one of these cars? How well did you first backyard project work?

Menisk,

Since you ask, no, there wasn't any FSAE when I was young.

But I did build something a bit bigger, at highschool, by myself. It went really well! There is a short thread about it (Gallery section, search "Young Z"), but it seems the photos disappeared when the Forum changed hosts. (I can dig up photos if anyone wants.)
~o0o~

Our team's philosophy is the simplest solution with the fewest parts because 9 times out of 10 it's the lightest and most reliable solution.

Me too. I am interested to see your version of "simplest". What Team are you, and will you be at FSAE-Oz-2014?
~o0o~

... it costs Honda millions of dollars ...
... To think that some sleep deprived student is going to ... end up with a better package ... is stupid.

Honda spend millions designing MOTORBIKE engines. Komatsu spend millions designing EARTHMOVING engines. Etc., etc. So what? You want an FSAE engine. Very different.

Look here (http://www.rotecradialengines.com/aboutus.htm) to read about two trade school boys who wanted to build an AEROPLANE engine. So they did! Fortunately, they only talked to Engineers AFTER they built it, otherwise my guess is they would have been told "IMPOSSIBLE!!!".

(BTW, one cylinder+head off that engine would also be a great starting point for a cracker of a little FSAE engine. Just DON'T get any Engineers involved! :) Their new site here. (http://www.rotecengines.com/))
~o0o~

... get out into your shed and build it, and then come beat us all at competition.

Since 2002 I have been lobbying the FSAE organisers to include at each event some "demonstration runs" from all sorts of non-FSAE, but small, racecars. So, different types of go-karts and other "mini-racecars". Let them clock Acceleration, Skid-Pad, and Autocross times, and let the students learn how simple it can be.

But, so far, NOTHING. (My guess is that the organisers fear the reality of it all.)

Should this ever happen, and especially if Prize Money is offered ($ = :)), then I will certainly get busy in the shed...
~o0o~

... learn to encourage students ...
... learn how to play nice ...

The real world is NOT NICE!

This is perhaps the biggest problem with the Modern Education System. You will eventually learn this reality, but it would be nice if your teachers let you in on this secret a bit earlier (ie. the occasional "old-school kick-up-the-bum" can work a treat).
~~~~~o0o~~~~~

Tromoly,

I would have sent the CVT drive FORWARDS to a Secondary-Shaft under the seat-back. Plenty of room there (ie. move any junk there elsewhere). From the SS a chain-drive would go rearwards, just to right of engine, to a diff/sprocket mounted just behind the engine. Or a two-speed Jawa-style gearbox and clutch could be mounted in front of the engine (ie. as the "SS"), instead of the CVT.

From the photo I reckon the rear-wheels could move a good 0.4 metres (16") forward. So front-wheels also move forward, and driver's feet are now about on front-axle line.

Not sure what to do about the flooding though? Gumboots for all??? :)
~~~~~o0o~~~~~

Christian,

Cardboard-Aided-Design works a treat with those uprights, too. Try "cornflakes packet cardboard" for your modelling. Cut with Mum's scissors, weld with masking tape or hot-melt glue. Think through the process of assembling it all, while doing this "CAD".

I suggest ~1 mm thick sheet steel, although slightly thicker (~1.6 mm) is easier to weld. Have the sheet completely surround the central bearing support tube, so only a circular weld at each end of this tube. Weld with "TIG" ("inverter" machines are dirt cheap these days, and you can buy "throw-away" gas bottles). Give several Team members plenty of practice welding scrap off-cuts. No heat-treat is necessary (other than maybe a lick of oxy-flame), but do final machining AFTER welding.

Importantly, try to find a "bloke-in-shed" who knows all this stuff, and ask for tips.

More importantly, there is not a lot you can do about "ultimate best weight distribution" now, so aim for "better than last year", and focus on EARLY BUILD FINISH.

Z

Luniz

11-10-2014, 03:06 AM

Z, Menisk, others: Would you mind continuing your argument elsewhere, preferrably offline? It has kind of steered away from the original topic and onto general FSAE philosophy and rules committee bashing, as usual...

Christian: You're right about the uprights! Welded sheet metal has the advantage that you can make them by yourself and a 10% increase of stiffness in the upright probably gives you more performance gain than a 10% decrease in weight...

Concerning the brake cylinders I posted earlier, yes I meant to say 8mm rod ends... In case anyone is interested, they're made by a VERY small company in eastern France called "Beringer", their lead times are sometimes a few months and sourcing them can be quite tricky.

mech5496

11-10-2014, 03:28 AM

Lutz if rodends are 8mm, it is not particularly compact. I know for isntance that AP makes one pull-type model that is really small and light (we use them since 2010). Beringer makes some top-notch components for Supermotos and go-karts, so they might worth a look as well.

ChristianChalliner

11-11-2014, 07:36 AM

Forbes - Yes I did find that document and presumed it was the one mdavis was talking about, thanks anyhow :)

Z - It would be good to see those photos! Interested to see the results. The CAD design for the uprights is a good shout and actually something the eco team have already done for some of their folded alloy parts so I'll mention that to the uprights guy. We have a good welder who can weld thicknesses as low as 0.8mm with TIG effectively so there's no issue on thinner material, of course final machining will be done after welding otherwise the bearing housing would not be round :) We are definitely focusing on an early build finish although it has been put forward that we are over stressing some of the members somewhat but I believe it will be worth it in the long run.

Luniz - Looks like we're going down the right track on that one then, it also has the advantage of being significantly cheaper than CNC'd alloy and can be produced much faster (no need for extensive CAD models, etc). I will look for the master cylinders later.

Mech- That would depend on what you consider compact, I have no arguments with an 8mm end if the cylinder itself is tiny, likewise I have a problem with a 6mm ended component that is enormous!

I did plan on writing a lot more than this but things came up as usual :( Again, thank you for all the help all of you.

ChristianChalliner

11-11-2014, 02:10 PM

Firstly, sorry about the double post!

Secondly, I've drawn up a rough idea for a front beam axle using 4 trailing arms which is similar to how the ECU car is at the rear. The basis of the design (described in RCVD on page 6XX, sorry I don't have my copy right now) is one where the lower links join up to form an A-frame and the upper links are parallel.

The problem I'm having is that it is not possible to have the upper links exactly parallel because then they would be sticking excessively far out from either the beam or the chassis. What this means is that the convergence point for the upper arms is reasonably close to the car so when the roll axis is drawn between the upper and lower convergence points it is excessively steep. If I understand RCVD the roll axis slope is equal to the amount of roll steer, in which case what is shown below would be ridiculous!

I CAN lower the roll axis to around 1 degree of roll oversteer however, this then means that the upper arm is sloped downwards a large amount. I will confess now that I don't properly understand anti-dive and anti-squat so I'm not sure on the effects this will have, if it is similar to a double wishbone then surely sloping the upper arm downwards will promote a pro-dive effect?

Anyway, the pictures can do it more justice than my explanation so here goes:

http://i1296.photobucket.com/albums/ag13/challicm/BeamFrontSideView_zps0f1a53db.png

http://i1296.photobucket.com/albums/ag13/challicm/BeamFrontFrontView_zps7345deaf.png

I appreciate that there are other issues with this design and I'm working on solving them however, inputs are always welcome :)

The main reason for picking this design was that it places the roll center in the 5-10cm region that Z recommended and that it also makes fabricating the lower arms and beam easier: simpler jig, one less spherical, less welded tangs on the beam, etc.

11-11-2014, 07:05 PM

Christian,

Will post Beam-Axle suggestions in a few more days...

My laptop power supply EXPLODED last night!!! Big fireworks. Burnt a hole in the table! :( So battery now draining lowww....

Z

DougMilliken

11-11-2014, 11:43 PM

My laptop power supply EXPLODED last night!!! Big fireworks. Burnt a hole in the table! :( So battery now draining lowww.... Z
Seems like your life is always dramatic(??) Fwiw, I've run a laptop (power supply label says 16V DC) from the ~14V in a car (with alternator charging). Might not charge the laptop battery, but will run the computer.

Loz

11-12-2014, 05:37 AM

Christian

Looks extremely similar to the beam axle on the front of the 2010 ADFA car. Although, the ADFA car used a pair of leading arms converging at the centreline under the vehicle.

http://s27.postimg.org/6r0sxatf7/ADFA_front_beam_axle.jpg

Before you get into any kinematics, there are lots of other considerations you need to work through with statics (although from your drawing the design is already heading beyond conceptual design and into detail design - not what I would call "rough").

The design (beam or otherwise) needs to first be able to appropriately transmit the tyre forces into the body while static (i.e. we are talking about action/reaction and stress/strain, although more specifically, managing system compliance).

With a beam axle the steering concept should also be well thought out and derived early in the process so that you have a good understanding of the nuances which will likely point the approach in a different direction compared to that of independent suspensions.

Even though a beam can be a simple system which delivers a range of favourable system attributes and can enable the delivery of a high performing vehicle in a short time frame, there are also just as many opportunities to fudge-up the design as there are with double A-arms etc, if you are not careful.

Fortunately, the good news is that with some logical thought, application of engineering fundamentals (primarily dealing with forces) and purposely keeping it simple, you can avoid crossing paths with many gremlins that may bite.

Loz

ChristianChalliner

11-12-2014, 07:31 AM

Loz - You are correct in thinking it's extremely similar, that's because to me it seems it is the best way of fitting a front beam under the car in the style I intended to use, I did try a folded structure type but found it tricky to fit underneath the body whilst mounting the damper to it in a manner that meant I was meeting the minimum travel requirements. By the time I had got it to work I had something which looked suspiciously like a big U shape so decided to try just a bent tube instead which for the most part fits the needs well and cuts down on the manufacturing.

I understand that the steering is tricky, I have put some thought into it already although I've not written/drawn anything out that I can show yet but I was thinking along the lines of a system which went: Steering wheel > Bevel gearbox > telescopic column vertically to floor > steer arm > link out to upright, along with some manner which coupled the column length to the axle vertical movement in order to prevent wheel toe changes, something even as simple as just a point on the axle which pressed on the underside of the steer arm on the column would do it? I was also thinking that there is no rule stating that both wheels have to be steered independently so why not steer only one upright and run a large link between the two behind the axle line? would give good ackermann I reckon...

Here's some pictures of the arrangement with lower roll steer but resulting in a more aggressive VSAL:

http://i1296.photobucket.com/albums/ag13/challicm/BeamFrontSideViewShort_zps2ada4143.png

http://i1296.photobucket.com/albums/ag13/challicm/BeamFrontFrontViewShort_zps35986e3d.png

I also have some impact attenuator points I've been asked to discuss by the guys who are working on that. We have an Instrom testing machine capable of performing slow crushing of components (so not a true dynamic test) however, every time we've made up a standard impact attenuator and mounted it to a bulkhead the result has been what is shown below:

http://i1296.photobucket.com/albums/ag13/challicm/899F283D-E94B-4F04-8474-C2053EC02E4C_zpsx3703wj2.jpg

http://i1296.photobucket.com/albums/ag13/challicm/56592A85-A75F-462E-9078-0921EE9A157B_zps7pyrxbuc.jpg

For this test the absorbed energy was 4100J which is both below the minimum 7XXXJ required and clearly the bulkhead has collapsed/deflected beyond the maximum 25.4mm , the deflection of the system was 150mm. I did not conduct or view the test but I can ask any questions if anyone has any.

mdavis

11-12-2014, 08:31 AM

Christian,

Are the tubes in your frame free to move in the lateral direction (the way they splayed out during testing)? If not (hopefully not), you may want to constrain them. What we did was put some sheet steel (I think .065, extra from making bulkheads, but whatever is laying around should work) strips between the 4 stand-off tubes. This constrained them to each other, and fixed our very similar problem. Make sure you constrain both directions, otherwise the bulkhead will bend along a different axis.

-Matt

ChristianChalliner

11-12-2014, 08:39 AM

mdavis - Thanks, yeah we did think about doing that for our next test and it was actually something we mentioned before we crushed it so we will try that :) Also, some clarification about the deflection, I've now been told that the plate only began visually deflecting after the instrom measured 150mm deflection so I assume the attenuator had already deflected around 150mm before this happened.

Jay Lawrence

11-12-2014, 09:44 PM

Christian,

I don't believe there is anything stopping you from running you steering link from upright to upright, though I imagine you will have a hard time packaging it. Also on steering: the ADFA car shown above had issues at comp (may have been 2009) with a very similar design wherein they had to run their wet tyres in order to meet ground clearance rules due to the location of their steering rack. At least that is what I was told, and they were certainly running wets when the weather was fine. Also, there's obviously some linearity concerns with those ADFA steering rods, but you're probably already aware of that. Just some things to be aware of with this type of design.

ChristianChalliner

11-14-2014, 05:42 AM

Thanks Jay, good point on the link running across the car, I hadn't picked up on that somehow, there are ways around it I suppose but it would result in multiple links and presumably lots of system play. That's a strange one on the wets as unless the car didn't meet the 25.4mm minimum bump travel or the rack was touching the ground I can't see how it could have failed to meet the ground clearance rule.

With regards to the steering I've been going through a few rough ideas, it seems fairly simple to make a telescopic linkage which actually physically connects and steers the wheels but the tricky part is actually altering the gear ratio whilst turning the shaft through the 80-90 degrees. It seems obvious to say bevel gearbox but finding one that isn't just a 1:1 ratio or enormous has actually been quite hard (I haven't found one yet). Another issue with the bevel box is the positioning of it in the car and the fact it reverses the shaft direction, seems easy enough right? just flip the inboard steer arm around... But that creates another problem in that then the shaft will be coming down rearwards of the FRH and it makes it harder to achieve good ackerman (at least with rearward pickups on the uprights). So I looked at another solution, a double UJ to turn the column through 80-90 degrees but then you start to end up with stupidly small steering wheel angles creating very high wheel angles unless you make the inboard arm very small which creates YET ANOTHER problem in that then the outside wheel wont turn at all in comparison to the inside wheel, in short, this is a complete pain and there seems to be no way of having your cake and eating it!

I'd rather not have to make my own bevel gearbox but I suppose that would be a possibility if I can find somewhere to cut the gears for me.

I think there must be a few arrangements I haven't yet tried which I need to which will solve the above, I'm sure it's possible, I've just not hit on it yet.

Mitchell

11-14-2014, 09:04 AM

Have a look at the ECU steering setup, would work well for beam axles :)

JSR

11-14-2014, 10:46 AM

We also had this idea for a pedalbox...

http://i1296.photobucket.com/albums/ag13/challicm/EDB2D855-7CB8-4FAE-905E-0BCFDD61A2CB_zpsfhwpd73b.jpg

Which removes the excessive length of this current one

http://i1296.photobucket.com/albums/ag13/challicm/723FF2A7-4093-4D5A-A34E-CDDB4938AE7D_zps2ikcrkgd.jpg

Maybe something like this then: http://www.fsae.com/forums/attachment.php?attachmentid=415&stc=1&d=1415979894

ChristianChalliner

11-14-2014, 03:53 PM

Mitchell - Thanks! will do :)

JSR - YES! Exactly like that, even the tilting of the cylinders is how I was going to do it but perhaps even more aggressively and then tuck the reservoirs away in a frame gap covered by a thin non porous skin/bag (no heavy plate or 'shield').

I've been looking at the beam axles thread, some (lots) of interesting stuff in there. The Cylindroid concept helped my understanding somewhat, or at the very least affirmed my view (perhaps mistakenly?) that movements about the roll axis will have an effect on the pitch axis location, movement, rotation, etc. I'm also fairly sure that the compromised anti-dive geometry in favor of lower axle roll steer is the better of my two posted ideas, it's still not ideal but it does have the advantage that it would be rather easy to integrate into a chassis design. I also considered the implications of hanging hard points from the front bulkhead and main hoop, I came to the conclusion that it will/should work well when it comes to jigging the chassis since they are both 'main' interface locations on the car (and the FRH for the front shock mounts). This would be helpful since I've been told that the last chassis was awful to jig up.

The beam axles have been received favorably by team members especially after a quick chassis concept was drawn up demonstrating how simple the frame can be made and was somewhat hesitantly received by the supervisors but they've pledged their support to the idea if we decide to pursue it.

11-20-2014, 06:30 AM

Doug,

Silly me, with my old-fashioned views that exploding electrical appliances were somehow unusual. I have now been reliably informed that they are, in fact, everyday occurances.

Ahh..., progress..... Soon we can look forward to exploding Jumbo Jets..., every day...!!! :)
~~~o0o~~~

Christian,

Lots of new stuff now posted on the "Beam-Axles..." thread. Take your time reading through it, and feel free to ask for any clarifications (it was bit rushed, so I probably missed some bits...).

And photos now back in "... Adventures in Africa." thread (Gallery section).

Z

ChristianChalliner

11-20-2014, 09:35 PM

Thanks Z,

I had a quick look just now in the thread, my rear beam is very similar to your layout 4 (the lower arms converge almost to an A frame aside from the fact they have to skirt around the inconsiderately placed oil pan :P ), I'll write a bit more later/tomorrow and show some more sketches along with a preliminary pedal box design (it appears I've acquired a second project).

ChristianChalliner

11-21-2014, 06:04 PM

Hi guys,

Just a quick update on something I've been working on. It's not VD related (at least not in a suspension design/kinematics manner) as that will come later with many drawings plus ideas/explanations. It is however, my first step into braking systems and I believe some background information is necessary.

Last year at the competition we had a hard time passing the brake test because the front wheels struggled to lock, in the end they did but with high tyre pressures and some rather suck it and see balance bar adjustment. So for this year I've made up a spreadsheet using the formulas found on the StopTech website and I'm convinced I must have made a mistake somewhere. This is because the calculations show that the current brake system is way over spec'd with even a modest applied force resulting in what would be a wheel locking situation at best and neck snapping at worst if the tyres were able to generate the required mu values.

So as far as I can see this means either one of two things:

1. My calculations are incorrect

2. There's something wrong with the system on the car

I have attached my excel calculations for you all to look over. I tried to make it easy to understand what was doing what and all information is accurate and measured from the past car. I appreciate that there is no consideration for the weight transfer or the tyre mu values but that is because I reasoned there was no point continuing until the numbers were verified.

Thanks,

Christian

11-21-2014, 08:27 PM

So as far as I can see this means either one of two things:

1. My calculations are incorrect

2. There's something wrong with the system on the car.

Christian,

I assume that EACH of your (four x) calipers has FOUR x 1" pistons? That is, TWO pistons on EACH side of caliper?

If so, then my rough calcs give:
O/A Mechanical Pedal Ratio = ~3,
O/A Hydraulic Ratio = ~26 (= Area-All-Calipers/Area-Both-MCs),
O/A Wheel Ratio = ~1/6 (Mu x Rc/Rw),
for
Total Ratio = ~13.

(All good numbers, BTW.)

So,
1 kN Foot-Force = 13 kN Braking-Force,
which is pretty close to what you have...
~~~o0o~~~

So ... my guess is ... [drum roll ...] ... air-bubbles in the front brakelines!

This is a very common problem in FS/FSAE. Perhaps a result of students spending too much time doing "calculations", and then thinking it just has to be bolted together and it will work just fine?

So (if old car still working?), get a BIG bottle of brake fluid and preferably a "suction system" to fill the lines, or be prepared to turn the car every-which-way-up, and do a lot of shaking, and jiggling, (and cursing... :)), to get ALL the bubbles out.

(Note that bubbles in the front lines can let the front-MC bottom-out, so it stops working...)

Z

ChristianChalliner

11-21-2014, 09:08 PM

Z,

Yes that is correct, they are actually these calipers: http://www.apracing.com/product_details/motorcycle/brake_calipers/motorcycle_rear_2x2_piston_caliper/cp4227-2s0.aspx

I think I'm with you aside from you've taken the pad material mu to be 0.55 whereas my selection from the list was 0.39 because I don't actually know the pad material so I assumed worst case, I will be ordering new ones at some point anyway and most likely the 0.55 ones.

That's quite possible as we did have a line failure at the competition and as the caliper has two inlets and two vertically opposed bleed nipples for each piston pair it makes it somewhat difficult to bleed (we found the best thing to do is actually remove it from the car and stick some plate in the caliper to act as a 'disc' for the bleeding process). We do have a suction system which we will be using this year :) Unfortunately, the old car is no longer in a running state but the brake system is still intact.

My next brake system quandary is bias bars! I understand the principle in moving the force application point along the bar so simple moments tells you that it splits the force as such however, the operation itself is somewhat mystifying, especially when the bar is not just moved laterally but then set so that it is not perpendicular to the master cylinders!

Some rough CAD ideas coming tomorrow along with comments on the front and rear beams, problems and thoughts :) But put simply, I think I'm in trouble at the front and that I've backed myself into a problem which will take significant work to resolve.

Mitchell

11-28-2014, 09:02 PM

Just thought you might like a source for some steering components and ideas:

http://www.hyperracing.com/pages/products/online_store.aspx?category=12500

Luniz

12-01-2014, 10:23 AM

Z,

Yes that is correct, they are actually these calipers: http://www.apracing.com/product_details/motorcycle/brake_calipers/motorcycle_rear_2x2_piston_caliper/cp4227-2s0.aspx

With these calipers it is highly likely that there is air in the system somewhere as they're next to impossible to properly bleed. The only reliable way I found after days of trying was to run brake fluid from a pressurized container (read: coke bottle...) through the system with the caliper in my hand and slowly turning it over while the fluid is "running" through. There is one place in the caliper where air will almost certainly be trapped if you don't move/rotate the caliper while bleeding.

ChristianChalliner

12-02-2014, 09:07 AM

Hi everyone,

Luniz, Mitchell thank you for the link and also for the advice on the caliper, a few years ago there was a part machined where someone tried to link the two line inputs on the caliper to each other in order to remove the T-piece connector in the lines, I'm not really sure what happened other than I was told it didn't work particularly well, I can only assume that what had effectively happened was that the connector had been screwed into the adapter such that there was no fluid flow to the upper caliper pot. Personally, I think it's worth doing properly again at some point but needs the proper research and testing carried out as running a line splitter hovering in free air doesn't look particularly nice or fill me with great confidence.

I'm sorry it's taken so long to update this with any real information, there were a few issues last week which prevented me from doing any significant work however, I do have a rough CAD drawing for you all to look over/criticize/etc:

http://i1296.photobucket.com/albums/ag13/challicm/19-11-14carshotFS_zps17aeadd5.png

So a quick rundown. We've decided that we would like to do a front and rear beam, the reasoning behind this is that a rear beam has been proven to work effectively and package very well (certainly in the case of ECU and UQR), we'd also like to do a front beam as running through the manufacturing we reckon we can build one much faster than last years double wish setup. Another reason is that looking at UQR's car it looks like they are running very short FVSAL's to give similar camber gain in roll at the front to their rear beam. In our opinion this compromises the chassis at the front end as it forces you to place either the upper arm attachment points in the middle of a bar or the use of more bars to triangulate the points whilst still meeting the frame rules.

Another main aim of ours is to reduce the frame weight by at least half, using a front beam allows us to remove even more bars from the chassis and also removes the need for the chassis to have sufficient stiffness to prevent camber compliance issues, we fully accept that it does NOT remove the need for the chassis to control the axles to prevent them wandering left/right and likewise that the beam then must have sufficient stiffness to keep camber compliance to a minimum.

Both beams will be constrained via 4 trailing links geometrically positioned to 'lock' the axle in place horizontally, the front beam lower will have actual convergence of the lower arms at the center of the beam, if my understanding is correct this places the roll center around 40mm above ground with the upper arms running as close as parallel as possible and sloping downwards in order to give a near horizontal roll axis to reduce roll steer. This has caused issues as it results in a short side VSAL which might lead to axle hop but I am not entirely sure as I don't fully understand the theory behind anti-dive/squat/etc.

The rear beam will be similar to the front however, there wont be a physical convergence point of the lower arms since the arms have to run around the sump, this also puts the roll center higher at the rear which if i understand correctly means that more load will be transferred geometrically resulting in faster response however, that is for independent suspensions so I am not sure if this is still true for beams.

The biggest problem is steering the front beam, in comparison to a double wish setup it is a real nightmare in my opinion, it's easy to draw up some ideas that 'might' work however, putting one into practice is significantly different and more difficult. My favored layout currently is one where a bevel gearbox is positioned at the top of the car with a 3:1-4:1 ratio attached to a column which runs down to the floor of the car and sits in a bearing housed in a cross member, the lower segment of the column is splined with a internally splined sliding pitman arm attached, this arm is then pushed up and down the column as the beam moves up and down thus preventing any wheel angle changes since the links remain the same length in relation to the beam. The issue with this method is that in order to get even 100% 'ackermann' gives a system where the uprights are steered from the front potentially resulting in an interference issue with the beam. Posted below are a few very rough drawings of various systems(some may not be accurate since they were only intended to show the method of steering the axle rather than the actual generated geometry):

http://i1296.photobucket.com/albums/ag13/challicm/152F5FA7-6E85-4332-AAE3-811878CCAD78_zpsewlhfvxw.jpg

http://i1296.photobucket.com/albums/ag13/challicm/056AF40B-CB03-4F01-8548-7AF04CE95B38_zpsu21dliug.jpg

http://i1296.photobucket.com/albums/ag13/challicm/F2617A8D-C00C-47CB-B2A7-CF5C13AFAACD_zps6y1vgo7x.jpg

(sorry about the general poor quality of the drawings and handwriting)

Finally, yes our beams look similar to those from prior art cars, yes I accept that it could be considered 'copying' by some but in our opinion it is fair game so long as we understand why we are doing what we are doing and our targets, plus, it's not like everyone accuses each other of copying their double-wish setups is it?

Onto a few extra things now. We have a set of cane creek DB coil shocks currently, in our opinion they don't fit in with our car concept since why does a car which is simple and for the main part non-adjustable need 4-way adjustable damping? It doesn't. We will do far better to run a fixed car and learn from it than we will by getting lost in adjustment. From a quick browse around it appears that the Kaz Tech quarter midget shocks will fit in with our car well, they are non-adjustable without a rebuild however, providing the dampers are spec'd within reason they should fall close to the 'optimum' required. They also lend themselves better to direct acting and potentially mono-shocks in the future since they have 70mm of travel.

I was also having a look around for some 8inch wheels and tyres to be used in the future. I came across these 'mini-cup' cars which for a start look like fantastic fun! (http://www.americanraceronline.com/tires/mini-cup/) and also have a slick pattern up to 8inch wide, I also found the chassis manufacturers site and a few photos to show how everything is packaged, if anyone is interested they can be found here: http://www.ncchassisco.com/chassis/mini-cup.aspx

Anyway, enough for now, see what you guys think!

Christian

MCoach

12-02-2014, 10:31 AM

Hey Christian, quick note on the American Racer tires ('Merica!). They are meant to be used in a spec series and used to help control wear and cost. Where as the Hoosier LC0 for minicup cars may last a night or two or less considering how much the amateur circle track guys dope their tires, the American Racer tires are meant to last a whole season with some left for testing. Here in the US, California-Berkeley and and Oakland University have both tried them with ill success. They are cheap on price, just right on size, but have been described to me as "driving on ice cubes". So far, I don't think anyone has discovered the magical "competitive 8 inch tire option" and typically anything this small is meant for small kids so it's not like they are marketing towards FSAE in anyway.

I think you might want to shun the idea of the hydraulic rack due to driver feedback requirements. Also, I'm not sure if it's legal.

Your chassis looks legal but you may want to check against a simulation as to how stiff that iteration actually is and if it meets your chassis weight/stiffness requirements. As a spaceframe team, one thing we did to great extent last year was use all of our body panels for chassis stiffening by making them load bearing. It helps narrow the gap between monocoque teams and space frames in stiffness, but you'll still be at a large deficit in weight compared to well done monocoques. I think ETS may have 40lbs less into their finished chassis than we do.

Have you considered ditching the third pedal? The clutch is only really utilized when getting the car going from a stop, so it may be more space efficient for you guys to move it to a handle somewhere. The ability to drive two footed with a bit more luxury/space between the pedals is also nice.

The Kaz quarter midgets may not not be adjustable without a rebuild kit (which means if you should get these shocks, get the rebuild/shim kit) but there is one thing that they have over the double adjustables: springs that fit with rates that are available in 5lb/in increments. The double adjustables as well as many others like Ohlins only have springs available in 25lb/in increments. It means you can get that much closer to dialing in your suspension to get exactly what you need. On the spot adjustability is the only thing you're missing out on.

On note of your rear structure I believe that your fuel tank needs to be protected in side view from anything that could get to it which I don't think this iteration currently does, but that just may be the angle unless there is space in front of the main hoop you're utilizing.

What differential do you plan on using?

ChristianChalliner

12-02-2014, 12:28 PM

MCoach - thanks for the detailed feedback :)

It's a shame the tyres are like concrete but maybe in the future it will be a viable option, as much as i loved the idea of making tyres like Delft i don't think it is ever a possiblity for our team so that kind of drops the 8inch wheels. Still, i think there's a lot of potential in the 8's if they can be made to work.

The hydrualic rack issues are something we're aware or and certainly legality is questionable, i have asked the Rules body to see if it is legal but i have yet to hear back, i understand the feedback loss is problamatic but i think it would be a good solution for a front beam if that could be considered manageable. One thing i was especially worried about with this setup was how to prevent the fluid boiling, i know that's a problem some of the UK drifters have and end up running power steering fluid coolers.

Bonded panels are on the list and we have a person who intends to do this but that's as much as i know currently.

See the third pedal is an interesting one, we currently have a centrifugal clutch in the car but it's never worked very well so that's why we made the decision to go back to a manual clutch this year. I'd prefer a hand clutch but i'm not the one making the decision on that but i will put it forward.

That's good news on the shocks, i know about the rebuild kit but quite honestly i'd rather not get one for this year or until someone comes along who i think is an appropriate person to rebuild them, basically, i don't trust any of the current members enough to rebuild them without screwing it up, not even myself at this point. So the less 'oh we could change this' the better i think.

Fuel tank will be of a triangular shape and pretty much the drivers backrest, we intend to have the driver sitting on the firewall which is inturn just infront of the tank, we will need some shielding to prevent the tank being heated by the manifold but we believe we can implement this without problems.

The diff we plan on using is the drexler but i think if i had unlimited choice i'd use a spool and have a good look at the geometry on go karts to see how they unload the inside wheel in turns. Why a spool? In my opinion i think you can build a very simple car that performs reliably, is easy to build and is fast without adjustment. As far as i'm concerned in our current state adjustment will only lead us down a blind alley so i'm trying to remove it where possible.

That's probably made a lot of people groan and question how you can have a car without adjustment but honestly i think we will learn more and be faster by just driving around any car problems we have and then working on those problems next year or if they're exceptionally bad we can always make a new part.

MCoach

12-02-2014, 07:48 PM

Depending on how much of the cars goals and requirements are based on previous cars, the design might be down a blind alley and you might not know it yet. I'm not saying you're wrong, just leave some wiggle room.

This year was our first car on 10s and it really is difficult to package things compared to a 13" wheel package. From talking to older members it had be done before, but poorly. From the time I joined the team we had always wanted to do it but there were so many opponents to it for various reasons...

But finally, we went ahead and did it anyway, however, we didn't really know where to start or where we wanted to end up. our 13" design could have just been scaled down but would that give us what we wanted? Maybe, maybe not. So we designed around what we thought it should be and gave it a lot of adjustment. Roll centers were 4 point adjustable front and rear, caster was adjustable by 6 degrees (ancient American secret), toe pick up points were adjustable through shims, a few more things than your typical FSAE car.

We didn't fully explore the adjustments before our stint at competitions this year, but it allowed us to take a look at where we may have been off, regroup, develop, and continue to understand how to better ourselves by educating ourselves of the consequences of moving it from it's adjustment and tweaking the adjustments as we develop new systems. We've only gotten faster since. So, some groans from me. It's nice to have the adjustment even if you may not readily use it. "Measure twice, cut once".

The way go karts unload their inside tires is a lot of caster. For an Aussie reference check out the Monash car from about the 2007-2009 era. I believe they ran a spool about that time. You could also ask them a bit about it's pros and cons and why they moved away from it. I think the Drexler is a solid choice based on the but have no personal experience with it.

coleasterling

12-02-2014, 08:58 PM

As far as 8" tires go, mini-cups are no good from either Hoosier or American Racer. They are both way too hard. Hoosier will not do a custom run of them in the LC0 compound, either (Believe me, I tried! I even offered to buy a full run myself.)

I personally think a Hoosier 42400 could be competitive. It isn't as soft as an LC0, but is a heck of a lot softer than the mini-cups. It is treaded, but how much does that really actually matter? The tires are cheap, so maybe some of the 8" wheel teams could try them out.

http://www.racetires.com/shop/42400-modified-midget-jr-sprint-micro-sprint-dirt/

12-02-2014, 10:04 PM

.. i think you can build a very simple car that performs reliably, is easy to build and is fast without adjustment.
... in our current state adjustment will only lead us down a blind alley so i'm trying to remove it where possible.
... i think we will learn more and be faster by just driving around any car problems ... and then working on those problems next year...

Christian,

Very well said, IMO.

For those students who disagree with above quote, be reminded that Christian's School is a perennial tail-ender at FSUK. Sometimes when you find yourselves at the bottom of a very deep hole, you have to abandon all ideas of fancy fully-adjustable, titanium-runged, carbon-fibre ladders, and just start climbing.

Big-picture work seems to be on schedule, and now that it is December you can start fleshing out the details.

(Although ... could you please add Percy to your CAD sketches (ie. the 3 x hip/shoulder/head circles + ~0.9 m long legs). Percy is the most major part of all the big-picture bits, so he should appear in all such sketches.)
~o0o~

More Detailed Comments.
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BEAMS - Have you seen my recent posts on Beam-Axle Kinematic Design (http://www.fsae.com/forums/showthread.php?1324-Beam-Axles-Front-Rear-or-both.&p=121931&viewfull=1#post121931)?

Your current ideas seem similar to B-A(4), namely a "W" shaped linkage in plan-view (with beam at top of W, and car-nose pointing down). This is similar to ECU's and UQ's rear-beam (edit: oops, not UQ), and is a good enough choice considering all the other FS bits that have to go with it.

Your front-beam also seems similar to this, but in side-view the links should be close to horizontal, to make the longitudinal n-lines through the wheelprints more horizontal (ie. ~0% anti-dive). (I still think the Model-T-Ford front-beam (ie. in Twin Beam-Wing sketch) is simply simpler, but it is a close thing.)

STEERING - Your BGB sketch is similar (I think?) to the arrangement on my B-A(5) sketch. I am quite sure that, if well-detailed, it will work fine. The R&P you drew will also work fine, except that most FS/FSAE R&Ps I have seen are poorly detailed! I would avoid the hydraulic-steering, except MAYBE as a 2-year project, perhaps started now, but not used til 2016.

Best is to stick to the earlier discussed aim of getting the whole car built early. Then, should some little details in the steering turn out to be less than ideal, there is still time for a bit of final polishing/improving before the comp. Worst case, in such an event you can always ask for suggestions here. :)

FRAME - "T3.12.5 The Front Hoop must be no more than 250 mms (9.8 inches) forward of the steering wheel..." <- This just a reminder.

Along with putting Percy in your CAD sketches, it is a good idea to give him some arms, and hands, and a steering-wheel.

Otherwise frame is OK. It will have lowish torsional stiffness, but with beams you can run springs that are so soft (or you can adjust handling via RC heights) that a wet-noodle frame will do.

For an easy approach to a simple+stiff frame, I suggest the minimum number of mandatory tubes (as you have done), then spot-weld a sheet of 0.5 - 1.0 mm thick steel (I suggest galvanised) to the bottom-rails. Use MIG with "spot welding timer" to fill ~3 mm diameter holes that are pre-drilled in the sheet every 20 - 100 mm. This means you do NOT need any tubular diagonal bracing of the floor, because the sheet does the bracing. And it also acts as ... a strong floor!

Add similar sheets (maybe even 0.3 mm thk) to the lower sides of the frame, make sure the MRH is well connected to the engine (because this acts as a "torque-box"), and the stiffness shoots up.

SPRING-DAMPERS - Again, the beams make this choice much easier. As before, with beams you can use very soft springs (ie. because no camber-change with Heave/Pitch/Roll), and with soft springs you only need low damping. The main decision here, IMO, is cost and availability. I would look for "low" and "easy". (Honestly, I reckon I could do it with some heavy-duty elastic bands! :))

TYRES - For future option of 8" wheels and tyres I would be looking to quad-bike off-road racing tyres. These are usually heavily treaded, but soft compound. So when half-worn they might work well. However, this would require the Team to do all the testing because (IIRC) the TTC cannot test 8" tyres (ie. too small...).

This is another good "2 year" project, where the student takes last year's car, retro-fits 8" wheels, etc., buys a trailer load of quad-bike tyres, then does endless figure-eights while logging lat-Gs, or just using stop-watch.

DIFF - Given you already have the Drexler, I would stick with it for now. Once the car is built and running, and assuming you have time, you can vary the Drexler so that it acts as anything from open to spool. Test to see what works best, or even "acceptably". If spool = good-enough, then make a bolt-on spool replacement for the Drexler, and save a few thousand quid in the Cost report.

Go-karts make a spool work by using Castor+Offset ... PLUS a stiff car (ie. mandatory no-suspension!). This also makes the driver work hard (ie. he has to lift the inside-rear-wheel up)! Heavier car = more driver work = ughhh! For your general set-up, I would suggest it easier to get a spool to work by fitting stiffer springs at rear (or softer at front), or a higher rear RC (up to ~axle-height), or both. This makes the centrifugal force at car CG do the work, and life is much easier for the driver.

LAST BITS - Miscellaneous comments based on quick re-read of your posts.

* Aiming for ULTIMATE low weight is NOT important now. Your good big-picture thinking will get you a long way in that direction. Your four-cylinder "ballast" stops you setting any records here, so your bigger-picture goals of getting the car built early and being well-tested are much more valuable.

* "Short SVSAL ... axle-hop" is NOT a big problem. If so, then after you post more detailed drawings I can tell you how to fix it.

* IMO, two-pedal car + hand-clutch = much better. Long term goal of "auto-box" (= NO clutch!) = even better! :)

Z

MCoach

12-03-2014, 12:05 AM

Erik, another quick note. Adjustments on systems don't need to be carbotanium or complicated. In fact, we didn't use either material for last years car.
for things like control arms or shims it can just be a matter of an extra hole or two drilled for the sake of knowing the difference in parameters and comparing calculations to real life. For shims it could also just be a matter of stacking washers in a different arrangement or more of them. I know that adjustable usually means more complicated, but there are simple ways to do some of these thing.

You caught me on the offset. Lots of castor + lots of negative offset could yield the opposite of desired results! :P
Lots of castor + some offset is enough to put your your desired tire in the air.

mech5496

12-03-2014, 03:54 AM

For an easy approach to a simple+stiff frame, I suggest the minimum number of mandatory tubes (as you have done), then spot-weld a sheet of 0.5 - 1.0 mm thick steel (I suggest galvanised) to the bottom-rails. Use MIG with "spot welding timer" to fill ~3 mm diameter holes that are pre-drilled in the sheet every 20 - 100 mm. This means you do NOT need any tubular diagonal bracing of the floor, because the sheet does the bracing, and it also acts as ... a strong floor!

Add similar sheets (maybe even 0.3 mm thk) to the lower sides of the frame, make sure the MRH is well connected to the engine (because this acts as a "torque-box"), and the stiffness shoots up.

Z

Agreed, the logis is the same with composite stressed panels but way simpler/cheaper. The Locost/Super 7 gang knows it for ages, with bonded & riveted aluminum panels dramatically increasing their torsional stiffness...

12-03-2014, 07:51 PM

MCoach,

It is true that making adjustable parts can be quite easy, such as your example of stacked washers, perhaps at each end of a toe-link to adjust bump-steer.

But the point I think Christian was making, and that I strongly agree with, is that it is not the MAKING of adjustable parts that takes the most time, but the TESTING of them. Especially as the number of adjustments increase, and the combinations and permutations skyrocket. And then you get lost...

Funnily enough, I reckon it is teams in the middle of the ladder that probably need the most adjustable parts. Teams at the top have already figured-out most of this stuff, so they just make parts with settings they know will work.

But the goal of teams at the bottom of the ladder is to "build a car that can drive 30 km at an average speed of 50 kph". If they can manage this before comp, then there is most to be gained by simply getting the drivers familiar with the car (ie. lots of seat time), regardless of the car's details.

Then, if still some time left, small ergo fixes (move the shifter a bit, make throttle smoother...), multiple tyre pressures to test, multiple static-toe settings, brake-balance, spring-rates, ... and the platinum-plated Drexler ("You mean we've had it for five years, and no one has ever adjusted it!?", which means resetting all the spring-rates again, etc., etc... There are a lot of adjustments that can be made on a very simple car.

If the team is successful (ie. finish mid-field), then next year they can start with mega-testing of last year's car, but retro-fitted with multi-adjustable-everything. Which is sort of the end of Christian's quote above.

Z

(PS. Or they can say "Engine, frame, suspension all look OK, so time to dive into this aero thing!".)

ChristianChalliner

12-03-2014, 11:15 PM

I'm short of time tonight but will get back tomorrow with more! In essence Z is spot on in terms of how he has interpreted my post, my feeling is that we are much more likely to get good returns from running many, many laps with fixed settings to get our drivers up to a reasonable pace both in understanding the car and the kind of courses they will be running on. As such, this is not the time to be making adjustments since it's 5-15 minutes per adjustment which is 5-15 minutes less running and practice for the driver! At this kind of level I'm firmly of the belief that 'improving the bracket which connects the wheel to the pedals' is the most important thing we can do.

Will get back with more tomorrow!

Christian

Edit: if the beams go well this year, next year I'm pushing for someone to do an un-sprung tray connecting the front and rear beams.

ChristianChalliner

12-05-2014, 05:00 AM

Finally got some time to write something not in a rush!

To start here are a few more pictures as to how the design has progressed, there are some issues with it. For example, the front roll hoop definitely needs to be raised for the cockpit template so I am already aware of that. With the accurate masses of all known components plus the masses of designed components with applied materials in SolidWorks the overall weight at this stage is 149kg of course this is still missing a radiator, exhaust, intake, diff hanger, etc.

http://i1296.photobucket.com/albums/ag13/challicm/FS2015ISOshotV3_zpse82661dd.png

http://i1296.photobucket.com/albums/ag13/challicm/FS2015SideshotV3_zps7010f2da.png

http://i1296.photobucket.com/albums/ag13/challicm/FS2015FrontshotV3_zps04ab1947.png

The mentioned issue about the steering wheel and front roll hoop is a definite concern and one that we've been working on. In essence it's driven by the desire to limit the number of tubes in the chassis, we didn't want to have to put in another roll hoop for the steering wheel since we already have the current one where the front shocks mount. It's possible to move it slightly rearward but then the shocks are inclined rearwards, I'm not sure how much of a problem this is, or if it is even a problem?

As Z pointed out the frame doesn't have to have high torsional stiffness since the beams are doing all of the work (aside from feeding in the arm loads and the SD forces) which is why we're not targeting high torsional stiffness but more an aim of reduced overall compliance. It was always our intention to have the floor as a 0.5mm sheet of steel welded in but we hadn't considered the reinforcement with spot welds so we will give that a try.

The steering is doing my head in, it's super super easy to run a setup which has reverse ackermann or even parallel steer but trying to run a setup with pro ackermann where there isn't interference with the beam, frame, shocks, basically anything.

There are carbon arms in those images currently but those are there because they are someones project, the first run of the car will be with steel arms and the car will probably run with steel arms at the competition but we can't stop people developing their own projects as they are what people are actually graded on rather than the car performance.

The pedal box and hand clutch I think needs reconsidering since the column does make it difficult to press the brake pedal in its current configuration and it's not really ideal to push the brake pedal further to the right.

At least the team is getting along better now and we're starting to get parts to actually work together now which was a big problem earlier on however, my frustrations with upper management are getting worse, basically because they seemingly have the whole process backwards, they're intent on having a chassis designed and built soon but I don't see the point because why on earth does someone want the part which everything bolts to designed first! Surely all the sub systems need to be designed first and then the chassis designed around those but that just falls on deaf ears.

In short, internal politics ruins everything, of course, these are only my opinions and don't represent those of the rest of the team/university, etc.

mech5496

12-05-2014, 10:53 AM

Good job so far! I believe it would be useful to add actual masses to all components to keep track of your CoG position and yaw inertia at the design stage.

The pedal box and hand clutch I think needs reconsidering since the column does make it difficult to press the brake pedal in its current configuration and it's not really ideal to push the brake pedal further to the right.

RUN A HAND CLUTCH! It is easier to package, lighter, provides better ergonomics, requires less parts to be manufactured, it is way cheaper. The easiest way is to add a tube near FRH and bolt a motorbike clutch handle directly on it. It is really easy to add a simple mechanical linkage to actuate the shifter as well.

Adam Farabaugh

12-05-2014, 10:53 AM

I think everyone seems to race to the goal of building the chassis, which is not a bad idea if you have everything designed before you start building it! You can look at some teams' facebook pages etc. and see that they are welding their chassis, which to me means that they must have already had their design freeze. Or are they really starting to weld without being 99% sure everything fits? I know I wouldn't want to angle-grind our frame apart...

MCoach

12-05-2014, 11:54 AM

If you're starting off fresh, parallel steer will get you a long way in this competition.

Taking a second look at your chassis the proportions seem a little odd to me. Is your front roll hoop waaay out in front of your driver or is your wheelbase really long?
In regards to that, there is a maximum distance that you'll need to adhere to for the distance from the steering wheel to the front roll hoop.

If you don't have a model of a 95% hooman, I'd suggest making Percy a solid model with some width to represent a normal driver. That may help decide some more of the chassis width with regard to the shoulder, hip, and thigh area of the car. Other than that, model the templates, I'd hate to see you roll into tech checking to see if they fit for the first time.

12-05-2014, 09:11 PM

Christian,

... we didn't want to have to put in another roll hoop for the steering wheel since we already have the current one where the front shocks mount. It's possible to move it slightly rearward but then the shocks are inclined rearwards, I'm not sure how much of a problem this is, or if it is even a problem?

NO problem. In fact, it is an ADVANTAGE (ie. "Mass Distribution Rule 1. All major masses to be mounted low down and close to CG."). I reckon the centreline of FRH can easily be ~0.2 m behind the front-axle-line (or more). With the top-SD-mount coming a bit forward from the FRH, and the lower-SD-mount welded to the back of the beam, the SD's final slope in side-view is just right.

(Edit: Also, having the SD slope from-wheelprint-to-CG helps better react all the major wheelprint forces. See below.)
~o0o~

More importantly, think about the structural performance of your front-beam-axle and its locating links. Consider side-view when under HEAVY braking. The bottom links are under GREATER (X-axis) tension than the actual wheelprint Fxs, and the top links are under smallish compression. BUT, because the bottom links are at 45 degrees in plan-view, their tension loads go up another 40+%. Right now I would not get into that car if it had (student!!!) glued CF-tube links!

But even more concerning is that these large bottom-link loads are reacted at the centre of the beam. So, at the very least, you should design the beam to be adequately strong and stiff against this LARGE bending load.
~o0o~

I don't want to sound as if I am harping on about this, but in your current layout I see a much better fit for the "Model-T" style beam.

This could have its main "apex-BJ" about half-way between your FRH and MRH, fitted to a lateral floor cross-member there (which is braced with the floor-sheet). Your diagonal SIS tube(s) would now be wide "V"s (in side-view) that meet this floor cross-member. The floor from MRH to the apex-BJ would be horizontal, for lower CG of driver+car, then slope upwards to clear the beam.

Importantly here, the largest front wheelprint loads of outer-wheel-braking+cornering are now fed directly through the beam's diagonal torque-arms, into the apex-BJ, and to the most central, and hopefully strongest, part of the car.

Lateral location of this beam can be via a P&S as in the "Twin Beam-Wing" sketch. Or via something like your bottom-link-wishbone, but with a Ball-in-Tube joint at the axle. Or, better yet, reverse your bottom-link-wishbone, and have the B-T joint under the front-bulkhead (so the bottom-link-wishbone connects to beam out near the wheels).
~o0o~

The steering is doing my head in, ...

Keep at it. It WILL work! :)

BGB with crown-gear ABOVE pinion. Rearward facing Pitman-Arm (as in your image). Angle of PA-to-Toe-Link (ie. along their "centrelines") less than 90 degrees. FORWARD facing Steer-Arms. Angle of TL-to-SA (along centrelines) considerably less than 90 degrees (say <70?). PA a bit shorter than SA.

Moving the spring-damper rearwards, as above, will help with clearance issues.
~o0o~

...my frustrations with upper management are getting worse,
... whole process backwards, they're intent on having a chassis designed and built soon ...
... internal politics ruins everything ...

I suggest that whenever the above "chassis first" ideas are raised in meetings, you raise a small 4" angle-grinder, and say, with TERRIFIED look on your face and tone of voice taken from that "Jaws" movie,

"Weeee're gonna need a BIGGER ANGLE-GRINDER!!!" :)

Seriously, keep reminding them of all the EXTRA cutting-and-butting that will INEVITABLY have to be done if they follow that course. Even when things go really well, there is always some rework. But try to keep cool...

Z

ChristianChalliner

12-06-2014, 05:06 PM

Mech - You don't need to convince me, I've been told "you go away, you come back with something that works and if we like it we'll do it" so that's easy enough with the bike hand clutch like you say.

Adam - Yup, well that's what happened last year, the amount of brackets and bars which were added in post paint was ridiculous.

MCoach - The front roll hoop really is that far forward, luckily we do have a person who fits the 95th pretty much identically so we're using him to make sure it seems reasonable along with the Percy template, it looks odd in the CAD but it actually works ok even if the steering wheel is right at the edge of the 250mm envelope.

Z - I see what you're saying and to be honest... I want to change it as for exactly what you're saying I realised I'd backed myself into a compromised design but I fought so hard to get the design accepted I fear that if I propose a new idea now I'll just be told to get lost. I'll work with the chassis guy though as an offshoot project to see if we can get a model T style beam in (I think it would work well as the anti-sub belts need a floor brace anyway so they can go in the same place as the beams ball joint). If I can get one in and with steering which works then I'll put the idea forward, my main concern is how I would make a model T style beam? It's easy to bend some tube to the shape I've got currently but it's a different story to start flattening tubes and still argue it's easy to fabricate! Also, I understand how the P&S works from a conceptual point as a lateral restraint but how does it account for the fore/aft movement of the beam whilst retaining pre-load as in your sketch?

Rearward facing pitman arm with forward upright pickups was the only way to get pro-ackermann steer when I was messing around with drawings, maybe I missed something at the time but all other configs ended up with parallel or reverse ackermann unless silly configurations were ran. Why do I want the crown gear above the pinion? Springloading gears together when the gears mesh in a conventional manner is pretty simple but I'm not sure how I'd achieve that through a 90 degree turn, unless springloading the crown gear against the casing would be enough? I don't know, I'm probably completely wrong!

Ahh if only that would scare them! I try and keep calm about it all but sometimes it's just impossible when people come out with the absurd, the idea that a bevel box and pitman arm is somehow more complex than a R&P is mystifying to me. But it is what it is and I just have to get on with it :)

Oh actually, just something that came into my head, I was considering purchasing an in-line bias adjuster to place in the line running to the rear brakes and removing the bias bar. My logic on this was that given that we have the same caliper size front and rear and the same master cylinder we are never going to run out of rear brakes. So reducing the pressure to them wouldn't be a problem and would simplify the pedal box, it would also mean that probably for the first time ever the bias adjustment would actually work! My only concerns are will the adjuster have enough range to be of use? I was considering that someone as a development of our car could place some in-line pressure gauges and find out what master cylinder size they actually wanted for the rear rather than just running the same as the front.

Christian

MCoach

12-07-2014, 11:19 AM

One thing that the beam axle does lend itself to is making unsprung aero really easy to do compared to most other suspension types.
...You know, food for thought when you get to that point. ;)

ChristianChalliner

12-07-2014, 11:35 AM

Oh I know, I've already said that if time permits it or at the very least next year someone should do a tray connecting both beams together so we can have a full length un-sprung aero tray. You know what I was told? "Yeah, lets just get this working first" :p

Luniz

12-07-2014, 06:22 PM

Just a quick advice on the brakes issue: The usual way to do this is designing a brake system that already has the desired balance set via the components (piston diameters, rotor sizes etc...) and just using the balance bar to fine tune it. I doubt that the adjustment range of a pressure regulator is big enough to offset the balance from 50:50 to what you need. Should be somewhere around 75:25 front to rear... But you need to find that out via CoG height and weight transfer. Doing this, you can then calculate the required line pressures and see if your regulator has enough range to drop the pressure to the desired value... but I highly doubt that.

ChristianChalliner

12-07-2014, 07:37 PM

Luniz, 75:25 is much higher than I expected, I was thinking more in the region 60:40. 75:25 to me seems like you will be locking the fronts up long before you're making full use of what you have available although it makes the car more stable on the brakes.

I understand that usually you would work it out that way but you're forgetting the strange environment I'm in, unless cast iron evidence that we need more front bias is presented it isn't accepted. So put simply if in testing the regulator is wound all the way to the front and the rears are still locking first I win as I've got justification to purchase a new rear master cylinder (cheaper and easier swap than rear calipers). It's possible to run higher mu value pads at the front to change the bias but it's doubtful that the pads front to rear will maintain the same mu value ratio across a run and wandering bias isn't something conducive to driver confidence.

Claude Rouelle

12-07-2014, 09:25 PM

Christian,

FYI the ideal DYNAMIC weight distribution in braking is 50 - 50, that is if you have the same front and rear tires That will tell you what your ideal static weight distribution should be for a given wheelbase, a given CG height and a given longitudinal deceleration ....which is dependent of your tire longitudinal grip. That will guide you to your front/ rear braking force distribution.

Beware that the ideal weight distribution in braking is not the one in cornering neither the one in acceleration; you will have to make compromise depending of the shape of your circuit.

Claude Rouelle

12-07-2014, 09:29 PM

Christian,

"75:25 to me seems like you will be locking the fronts up long before you're making full use of what you have available although it makes the car more stable on the brakes"

Based on what calculations?

How do you define stability in braking?

"as I've got justification to purchase a new rear master cylinder (cheaper and easier swap than rear calipers)" Or another front. But you should not go through multiple trail and errors sessions: simple calculations should tell you what master cylinder size you need.

12-07-2014, 09:57 PM

Christian,

Easiest first.

BRAKES - The Rules mandate two independent circuits for F/R. So tossing the bias-bar+2-MCs means you would have to use a larger "tandem-piston-MC" (ie. the type with two equal diameter pistons in series). And you would then still have to add the pressure limiter. So NOT much simpler than the bias-bar arrangement. The two-pedal + hand-clutch is a good idea though, and gives plenty of room for the bias-bar.
~o0o~

STEERING - Good ackermann comes from having the correct angles between the Steering-Tie-Rod and the Steer-Arm, and also between T-R and Pitman-Arm, when using one. Try angles of 60, 70, 80, and 90 degrees, in the directions I indicated in my last post. Then, from the observed pattern, home in on better angles. Start with the SA as long as possible, and make the PA about 70 - 80% as long. So, if PA = 100 mm long, => SA = ~130 mm long, AT LEAST.

"Why do I want the crown gear above the pinion?"

So when you move top of steering wheel to right, the car goes to right! :) (Ie. it allows rearward-PA, forward-SA, and generally good ackermann.)

"Springloading gears ... not sure how I'd achieve that through a 90 degree turn..."

Firstly, the idea of springloading the gears (as is done on all production car R&Ps, EVER!) is to eliminate backlash. Especially for the teeth that contact near straight-ahead driving, which wear down faster than the other teeth. The idea is to provide a "suspension" for one set of teeth that allows them to ride up-and-down as they roll over the worn-down teeth.

With BGB, my suggestion (in earlier post here and on "Beam-Axle..." thread +) is to have the pinion-gear-shaft mounted in the housing in the normal fashion, say on two deep-groove-ball-bearings. Thus it is fully constrained, except for rotation. But (!), the crown-gear-shaft is mounted in two bronze-bushes (easiest), or perhaps two needle-bearings (maybe next time), so that it CAN FREELY SLIDE VERTICALLY. So, only radial constraint, but free to rotate, and FREE TO MOVE AXIALLY (ie. up-down).

The last step is to provide a circular pad (preferably bronze, but steel will do) that sits on top-centre of the crown-gear-shaft, and has a spring between it and the housing that pushes the pad and shaft down (with force of ~10 - 30 kg?). The crown-gear is now always in tight mesh with the pinion-gear, but it can ride up-and-down as it rolls over the pinion-gear's worn-down teeth.

The usual "adjustment" process is to screw down the spring until it is coil-bound (ie. solid), then back-off about 1 mm. This allows ~1 mm of "suspension travel", but stops the teeth separating any more than 1 mm, so they don't slip over each other. And, BTW, choose gears with fewer but BIGGER teeth. This much better than many little teeth! I would like at least 10 mm pitch (ie. centre-to-centre of teeth).
~o0o~

MODEL-T BEAM - Engineers vs Artisans...

"... my main concern is how I would make a model T style beam? It's easy to bend some tube to the shape ...
... but it's a different story to start flattening tubes and still argue it's easy to fabricate!"

[Mini-Rant :)] IMO the "Meccano Set" of recent times has SET BACK Engineering much more than it has advanced it. Nowadays, and even back in my day, far too many young Engineers think that "engineering" is about collecting together large numbers of prefabricated parts, such as shafts and wheels and plates and brackets and things with lots of holes drilled in them, and then assembling said multitude of parts with another multitude of nuts and bolts and washers and other bits and bobs...

On the other hand, ... on the other side of the world, in any remote village in Africa, the approach is very different. There the young boys don't have the luxury of selecting from a multitude of prefabricated parts. Instead, if they are lucky enough, then, perhaps, maybe..., they might have some fencing wire. Maybe even a single pair of pliers, in the whole village. Although fingers usually suffice.

From said raw materials, namely a piece of wire, these young boys, maybe 10 years old, craft a small man about a foot high. Their creation has fully articulated arms and legs. He sits on a little bicycle, complete with rotating pedals and wheels. The young boys attach a long thin stick to the bicycle seat and push their creation around in front of them, with the rider's legs going up and down, and the wheels turning around and around...

Quite brilliant, really. From almost nothing, a small mechanical-man. Most ingenious!

But back in the civilised world, I suspect that most student Engineers, 20+ years old (and also too many Senior Engineers!), think that hammering a nail into a piece of wood is too difficult a "fabrication" step.

"You want to do what!!! How the (bleep!) are we going to write a Matlab program to calculate the optimum kinetic energy needed from that "ham-whatever" thing you're proposing... Geeezzz ... ya gotta think about the practicalities here!!!"

Anyway, (IMO :)) good Engineering is more about being able to do good ART, than it is about being able to do good calculations. When the "art" is right the product works. But good calcs with bad fabrication is just junk. [End Mini-Rant]
~o0o~

Soooo..., the skills you need are more black-smithing, tinkering, panel-beating, etc., and less Matlab-ing, Solidworks-ing, etc. As mentioned before, sheet-metal working skills for ~0.3 - 3 mm thick steel will get you most of the way. I find 1.6 mm, = 1/16", = 16 g, particularly easy and useful.

The main part of the beam is just a tube, as you already have. The two tapered "torque arms" can be done like this. Cut two wedge shaped pieces of 1.6 mm thick steel that are ~600 mm long, ~200 mm wide at one end, and ~100 mm wide at the other end. Use a folder or press to put multiple small bends in it, along its long axis, so that its cross-section resembles an angular C-shape.

Next, use blocks of wood and a biggish hammer, or a big vice, or a small hydraulic press, to squash the C into a taller-than-wide polygonal O-shape. IMPORTANT! Evict all Academic staff from the area while you are doing this last step, lest they have kittens. They are terrified of hammers! Seam-weld the joint with TIG. Best to have this joint on a corner of the polygon section for easier welding.

Lastly, weld the two tapered torque-arms to the main tube, and to a gubbin that carries the main apex-BJ (which should be generously sized, say 10 mm bore). Add some nice gussets at the triangle's three corners for a true craftsman-like job. Done!

Using only "Cardboard-Aided-Design" to get the right shape for the sheets before bending, I reckon about one craftsman-day of work to make the whole beam. Students will take longer, a few days or maybe a week, and should practice first on offcuts of sheet.
~o0o~

LATERAL CONTROL OF BEAM - For this, and given the frame layout you now have, I again suggest a Ball-in-Tube joint at the centre-bottom of the front-bulkhead, with a wishbone going back to connect to the beam via 2 x BJs roughly where the torque-arms attach to the main tube. The B-T could just be a rubber bush, because very little fore-aft movement there.
~o0o~

Ahhh... this would be so much easier to explain with a very simple sketching facility here...

Enough for now. I am heading down to Melbourne in the next few days, so may not be able to add much in the next week...

Z

Luniz

12-08-2014, 04:01 AM

I understand that usually you would work it out that way but you're forgetting the strange environment I'm in, unless cast iron evidence that we need more front bias is presented it isn't accepted.

Wouldn't a very simple weight transfer calculation at 1g of deceleration be "cast iron" enough to convince the decision makers of the need to run different size master cylinders? This kind of calculation should be understood even by the most idiotic white collar decision making tie wearers... Also, don't nail me down to that 75:25, could also be 66:34 or whatever. It's been a while since I have designed a brake system for my team and I can't remember the numbers any more ;-)

Luniz

12-08-2014, 04:11 AM

I just found an online calculator for the brake bias and punched in some ballpark numbers (13" tires, 25.4mm caliper piston diameter with 2piston calipers...) , and this is what I got:

http://brakepower.com/

But as a word of advice: Try to put your own spreadsheet together for this calculation so you can actually understand how it is done...

ChristianChalliner

12-08-2014, 07:45 AM

I don't have much time so I can't write a full reply but thank you all for the input (good to see you adding your thoughts again Claude :) ), I ran the numbers through that online calculator assuming a 1g stop and modifying the numbers until the front master cylinder came out at ~14mm (to match the current MC size) I ended up with the following:

http://i1296.photobucket.com/albums/ag13/challicm/Calculator_zps29142621.png

Numbers speak for themselves I suppose.

Will write a full response later.

Luniz

12-08-2014, 08:14 AM

You may have forgotten to add the driver weight, 220kg seems a bit optimistic for a first year, 4cylinder, spaceframed car on 13" tires, and I think you might have forgotten to factor the driver into the static longitudinal weight distribution as well, and I'd question the CoG height... Also, the rolling radius of the tires is a bit high, the hoosiers have 21" OD. But as far as the bias is concerned, yes, you are likely to end up somewhere between 60:40 and 75:25 depending on the numbers.

ChristianChalliner

12-08-2014, 09:00 AM

Luniz - Yep all correct! In my haste I made quite a few mistakes there, the radius should be divided by 2 and the driver weight should add ~60kg to the car weight. CofG has been calculated via the CAD models plus actual measure component masses but I do agree it appears optimistic.

Edit: actually i have no idea where that 305mm came from, should be 254mm.

ChristianChalliner

12-21-2014, 09:31 PM

Hi everyone,

So after being soundly made to look stupid in my last few posts here I'm back with some more on how we're progressing!

Firstly, I would like to give some 'real' justification for front and rear beam axles beyond the fact that they significantly reduce frame complexity and weight. At the start of this thread I talked about the uselessness of the Avon tyre data and was advised by Claude to seek out access to the TTC, I did, and was told that it was not an option to fund the resource. The reasons why it was rejected is beyond this thread. However, given that the previously mentioned Avon data is for most purposes useless, how would it be possible to decide upon a front view virtual swing arm length for a double wishbone system? what exactly would have been the justification without tyre data? beyond the original optimumlap sim I ran? With this being the case the use of beams makes a lot of sense for this reason alone, there is no need to consider a FVSAL because there are no compromises in pitch or roll, the need for tyre data to establish this parameter is eliminated.

I appreciate that other factors to be decided remain unchanged such as ackermann geometry, anti-dive, etc but there's considerable literature available to support various points and depending on the method of constraining the beams certain parameters are almost fixed by structural needs. Whether you consider this to be a disadvantage of a beam is up to you but personally, I find it advantageous as there is no 'black art' aspect involved, the answers can be found through first principle generated numbers.

Furthermore, comparison of last years car (in CAD) and this years car shows a considerable drop in yaw inertia (the actual numbers I have forgotten but we were talking at least 5%) this is because there is a much lower proportion of chassis members outside of the wheelbase and the pedalbox is 10cm shorter than previously.

Initial studies on the front beam also show a camber compliance in the region of 0.5deg/g, sounds rather large, so maybe something will be done to reduce this. But, consider this, the beams have FVSAL = track/2 in roll therefore, 100% camber compensation in roll, compare this to a car with 50% camber compensation in roll and is a compliance of 0.5deg/g really that bad when after 1 degree of roll a car with 50% compensation has already lost 0.5deg due to geometry?

Moving on, the upright steer arms will be 100mm long, this is a practical limit due to both the wheel and the desired wheel/wheel ratio, I initially decided upon a bevel gearbox ratio of 2.5:1 however, discovering that no one in the local area makes these ratios (and that trying to calculate your own gears and then finding someone to cut them is actually rather tricky!) I found a local supplier who will supply 2:1 and 3:1 ratios. Personally, I believe the 2:1 ratio will result in steering which is too heavy so I have decided the 3:1 is the best compromise. I have put together a brief set of numbers which are included as an attachment, the second tab includes the formulas used for calculating the 2.5:1 ratios in case anyone is interested. One thing I have been able to use the Avon data for is approximating the maximum self aligning torque (~90Nm) and then assuming this is being 'fought' by the driver to give the necessary torque the bevel gearbox must carry. I think I may have made an oversight here but I'm interested in what others have to say. Using these numbers gave a crown gear torque of ~70Nm, using a 3:1 ratio this drops to ~25Nm at the steering wheel, this is directly at odds with this article (http://www.sae.org/students/cockpit_control_forces.pdf) which suggests the the system should be designed for a steering wheel input of 100Nm. This being based off data of peak torques generated by test subjects, now, my question is, is my assumption that the 90Nm aligning torque as a maximum is wrong? or is it that these tests are effectively assuming that said person is trying to resist the tyre striking something such as a kerb?

This brings me to the next part of this problem, selecting a 'correct' gearset. The gears will be sourced from Cross+Morse (who are pretty local to the University) the data sheets are shown here: http://www.cross-morse.co.uk/pdf/Bevel%20GearsEN.pdf . After some testing (using a gaming wheel) we concluded that it's reasonable to expect the wheel to be turned at approximately 60rpm, following from this, the transferred power (assuming crown gear is made to withstand 100Nm) is 0.628kW. Looking at the data sheet (and assuming a moderate shock and light impulse modifier of 1.5) this suggests that gear set M501545 is appropriate but this gear set is enormous and heavy! with a crown gear of diametrical pitch of 225mm and a pinion dp of 75mm, this is unacceptably large and heavy (8.4kg!!!!), now, it makes sense that at higher rpm these gears can withstand higher powers as less torque is transferred however, I don't believe it right to just assume the rpm is twice as much to end up with a reasonable gear size.

But onto the rest of the car!

The front beam has been redesigned to be a leading arm with peg and slot lateral restraint, the reasons for this were discussed previously and have allowed the front roll hoop to move rearward by 200mm, this has also condensed more frame mass towards the CofG whilst retaining very similar chassis masses (difference of -0.2kg). One interesting thing is that with the rearward balljoint and the 'peg' placed on the chassis and on an axis parallel to the ground plane axle roll steer is reduced to zero throughout the range of travel WRT the body since this axis is fixed on the chassis. There was also the added advantage of removing any interference issues between the steering arms and the damper units. A few pictures are shown below:

http://i1296.photobucket.com/albums/ag13/challicm/FS2015ISO22-12_zps389f4e60.png

http://i1296.photobucket.com/albums/ag13/challicm/FS2015FrontBeam22-12_zps72fd9f13.png

I imagine most will note that the arms do not converge at the balljoint and hence put the lower link in bending, this is a further concern since in braking this link is also in compression, yes there is a buckling concern however, if the links converged at the balljoint housing then the driver would be sitting through the links! I'd also assume that it's noticed that the links actually pass through the frame, my understand is that this is fine providing they are shielded by a solid material (at least, that's what the rules say) thus, the floor will sweep over these links which will also form the leg support for the driver. In order to fit the beam in the car it will be welded up as shown in a jig before the upper links are cut out, sleeved and then bolted back into the beam, all this will be done in a jig to prevent any alignment changes.

The rear went from a folded construction to a bent tube back to a folded construction again. This was because the requirements changed, initially we were going to run rear uprights however, weighing up the benefits of the reduced complexity and weight versus the lack of adjustable toe we decided that integrating the hubs into the rear beam was a more worthwhile endeavor. Again the beam will be made up within a jig to minimize any resultant toe angles from construction. Please excuse the poor quality of the CAD, it was drawn up in somewhat of a rush.

http://i1296.photobucket.com/albums/ag13/challicm/FS2015Rear22-12_zpse893c9e2.png

Since there are no longer rear uprights and hence there is no longer a 'steer axis' my thoughts were that the center of the hub bearings have now effectively become the steer axis, as such, in order to minimize scrub radius and hence tyre advantage the beam has been pushed out as far as possible into the wheel, this has resulted in a scrub radius of ~50mm. The shock position results in a motion ratio of 0.5, yes this is digressive as the system will move similar to a scissor jack but it is yet to be determined whether this is a problem or not. The rear roll center works out to be 90mm, resulting in 1/3rd of the weight transfer being kinematically transferred. In contrast to the front 0.8 degrees of axle roll oversteer is present, this may be too much? but it is thought that this will help to turn the car into corners and reduce understeer common of FSAE cars, so passive steer effectively.

From a personal point of view tensions between myself and the 'management' have calmed somewhat but some issues remain. When a third year mechanical engineering student doesn't understand basic gear principle you know something is wrong...

Likewise, when lazy members try to take credit for my and the chassis guys work we can't help but get somewhat annoyed.

There's more I've forgotten I'm sure but that will be sufficient for now I'm sure, as always, feel free to throw stones/ask questions/etc.

Thanks,

Christian

EDIT: Oh and I've started investigations with one of the faculty advisors into the future development of an un-sprung undertray for this year or at minimum next.

EDIT EDIT: The front beam is not complete! so don't blast me for the peg and slot having no side support or the use of a single gusset for the shock support, the shock support will be boxed and the peg and slot will have side supports I just haven't drawn them in on the CAD yet because it's time I can better spend doing other things!

Pete Marsh

12-22-2014, 03:00 AM

Don't forget to add the Moments from the trail and offset to the self aligning torque of the tyre.

I think there might be some confusion between max design strength, and expected steering forces. 100Nm sounds like a reasonable value for the highest loads a person could exert, but is miles too high to steer the car.

Pete

12-22-2014, 03:13 AM

Christian,

Looking good. Just brief note for now ('cos Xmas-Chaos!!!).

Quick look at your gear charts, and I would pick either M251545, or maybe even M201545. The power ratings given (though I didn't look closely) are probably VERY conservative. The M25 or M20 gearsets can be lightened a lot by machining away much of the heavy bosses.These are made extra big so that customers have plenty to work with. Choose slightly bigger gears now, then next iteration you can go smaller and lighter and use the company's induction hardening services.

As theoretical check of your required gear tooth size just calculate what load at the steering-wheel rim is required to shear one tooth off its base, assuming tooth made of mild-steel. If this load is much bigger than, say, 100 kg, then unlikely the driver can do it. Plus you have the safety factor of the tooth being better-than-MS. And maybe add another SF = 2+?

The overall arrangement is really looking good. Track width looks quite wide though?

For the Model-T-front-beam I still suggest the tapered torque arms as suggested on page 12. This is also the way Ford, and countless others since, have done it. All round simpler, lighter, lower-CG, stronger, easier, +++. I will post another sketch on a slight variation to lateral location for this type of beam soon, but silly-season now...

Also good idea to build at least two of each beam, both front and rear. A "lightweight" one for initial testing (ie. to check compliances and ultimate strength) and a significantly stronger one for "just in case". So if the lightweight one fails just before comp, fit the heavier one, take the 5 kg (?) hit, and go on to complete all Dynamic Events. Note how UQ at Oz-14 had to significantly (!) brace their lightweight rear-beam just before comp, even though initial testing showed it to be OK. More testing = faster drivers = higher loads everywhere!!!

Z

mech5496

12-22-2014, 09:58 AM

Christian, seems you have made some solid steps since the beginning of this thread, keep it up! Adding to Pete's comment, think that you most probably need some camber/toe adjustment, as those are important factors to vehicle setup (actually near the top of the list together with springs/LLTD and tire pressures). Hint: Take a look at Z's adjustment method proposed on "Suspension Design" thread, where he talks about swing axles (cannot find the link right now)

Big Bird

12-22-2014, 11:19 AM

Wow. What a great thread! I've got some reading to catch up on here...
Nice work Christian.
OK. Digressive rate at rear. Therefore with weight transfer to rear (under accel) the ratio of F:R roll stiffness becomes more forward biased compared to linear rate. Therefore lateral loads taken more on front end than with a linear rate rear. Therefore less weight transfer across rear axle than with a linear rate rear. Therefore better grip under accel???
Does that make sense?

ChristianChalliner

12-22-2014, 03:07 PM

Pete, Ahh yes, thanks for reminding me! I had realised I was missing the mechanical trail x lateral force and the scrub x longitudinal force torques but at the time of writing I had forgotten that the initial investigation failed to consider these. Rather silly considering I talked about the scrub radius and resultant tyre advantage at the rear! You're correct that there is some confusion, from personal experience with torque wrenches, karts, etc, I was thinking that around 20Nm max for a 'normal' steering load but my argument is that if it only takes 20Nm or so to turn the wheels dry (and steering torque reduces at speed) then why is it necessary to design to 100Nm? It seems pointless to me because it is not physically possible to exert this torque and have the tyre react it unless the tyre is somehow bolted rigidly to the ground. You'll end up with a system somehow capable of transmitting ~300Nm to the wheels, also, I remember doing up flywheel bolts to 110Nm and I was using all my strength on a 0.5m+ long bar. Given this, I see 100Nm as a totally unreasonable load to expect the steering to withstand.

Z, the gear 'size' you have selected tallies closer to my original estimates when running through the ANSI document to size my custom gears, this would have resulted in a pinion capable of reacting approx 40Nm of torque. I will perform the shearing calcs to test the smaller gear set though and also contact the company to see what their specs really are. I agree that the gears can probably lose much of their weight through some 'lightening' holes and reduction of the bosses so I'll look into that.

The track width is 1200mm, from a rough drawing of the car inclined at 60 degrees we were unhappy with how close the CofG was to going 'over' the outside tyre pivot so when considering transient maneuvers and the early talks of lifting inside wheels I decided to bring it up to 1200, it can always be reduced next year if we think it necessary.

With regards to the tapered torque beams you're going to have to show a sketch or picture as I'm having difficulty understanding where you're coming from, I looked at model T beams and they appear similar to the one I've drawn albeit missing the upper links. This isn't exactly possible in our configuration unless the beam was inside the car. One option is to 'split' the pivots so that there is a pickup on either side of the car for each side arm pair, whilst this makes the structural issues easier and lowers the loads, since the convergence point of all 4 is now 'imaginary' axle roll steer is back to changing over the travel and the beam must also now be torsionally flexible otherwise it's over constrained. I suppose this is easy enough to do by cutting holes in the front view of the beam and might even be helpful for feeding air to an undertray?

The plan is to have two beams as suggested, one as the 'design' and the other as the heavy weight with double thickness of all sections.

Mech, thanks :) I see where you're coming from but I honestly believe we will benefit more from jigging something to spec at the rear and just driving what we end up with, any issues can be fixed next year. The front will however have both toe and camber adjustment, toe through the threaded arms and camber by having different housings slotted into the ends of the beam. Hopefully we don't have to use the second but it's possible if necessary.

Geoff, firstly, it takes a strong person to accept they were/are wrong so a big thumbs up for the UWA thread although I don't believe that you should be held to account in isolation but that is for another thread. Elsewise, thanks :) and yes that makes sense to me! Via a similar logic though front springs stiffening relative to the rear will give understeer on corner exit?

More to come soon, busy with Christmas!

Thanks,

Christian

12-22-2014, 07:24 PM

Christian,

Another short note...

Track width =1200 = good. Much more = too wide = too slow through the slaloms. Much less = too risky for roll-over, given unknown CG height and cornering grip levels.

For the tapered torque arms see this SLT-Swing-Arms (http://www.fsae.com/forums/showthread.php?8950-Suspension-Design&p=45363&viewfull=1#post45363) post. Try to make sense of the structure of the arms there, from the image and any words describing it (also more words in some later posts I think). Otherwise I can post another sketch later. It is all straightforward blacksmithery, and very useful stuff to learn for projects like FS.

For Front-Camber&Castor-Adjustment I suggest an adjustable, or replaceable, bracket between the beam and "upright", either at the upper or lower BJs (only one needs to be adjusted). (Edit: Angle-grinder and welder also good for adjustments here!) Toe is easiest adjusted via the toe-links (ie. conventionally).

For Rear-Camber&Toe-Adjustment you can use something similar to above Swing-Arm link.
BUT (1) if you can do a stiff, accurate, and UN-adjustable zero-camber&toe-angle beam, then that would be good enough. That is ECU's approach.
BUT (2) I also have another suggestion. Do the ends of an unadjustable beam with short horizontal-lateral-axis tubes at the ends that act as the bearing-carriers. Make these tubes with ID about 10 mm larger than the OD of your bearings. Then fit a sleeve inside these tubes that carries the bearings, and is clamped in place by the outer tube. Importantly, machine inner-surfaces of this sleeve so they are NOT parallel with OD. Say 1 degree out of parallel. Then, by rotating the sleeve you can get camber = +/- 1 degree, or same from toe, or a combination inbetween... Or replace sleeve with another one for bigger/smaller adjustments of camber&toe.

The "split pivots" twist-beam, with connection to chassis at each side, is a good idea. BUT (!!!) it requires considerably more structural know-how than the simpler Model-T style. Maybe for next time...

In side-view the Model-T apex-BJ only has to be about 0.4 - 0.6 metres behind front-axle-line. Not sure where yours is, but in plan-view an "X-shaped" floor brace, fitted between the V-shaped SIS tubes and the FRH, could carry the apex-BJ at its crux. (Edit: This structure would work very well for torsional stiffness. Think about the "load paths". Though tor-stiff NOT very important...)

Must now go a-visiting...

Z

Kevin Hayward

12-22-2014, 08:41 PM

Christian,

The ECU beam has shims to adjust camber and toe. Enough to be zero for accel, and a couple of degrees for skidpan. A shim in for toe adjustment, just to account for welding deformation. Nothing fancy, just thin shims inbetween a bearing carrier and the beam. The goal was to make it non-adjustable in the future once testing showed what camber was best to run. Not so sure anymore as the adjustment was very useful.

There are nicer ways of doing this. Z suggested machining the bearing carrier off axis to allow a few different angles depending on orientation.

Love the work by the way. Some nice simplifications and shouldn't be too hard to pull off.

Kev

ChristianChalliner

12-22-2014, 10:01 PM

Z - Yes that was the idea on the track, as much as was necessary to be 'stable' but no more :) maybe 1150 or less next year...

I have looked at the post you mentioned, I can see where they're going but if you look at the front beam and consider if you were to place one beam in the place of the two links. It would be around midway between them, trying this ends up with the arms intersecting the chassis quite catastrophically so the only way to do it would be to remove the upper link entirely and replace the lower link with a much thicker one. It would probably be necessary to fabricate some gusseting between this and the upper attachment point too, I will try this although initial attempts have not been promising! I'm just concerned I'd be placing a considerable bending load (pretty much the entire braking torque) on the attachment between the beam and the arm.

Front camber is adjustable by the method you mentioned already, those open box ends will have billets which connect to the upright, these will be removable and hence provide 'adjustment' probably only +-2 degrees of caster but easily enough camber (2,3 maybe even 5+ possible!).

I like the idea for the rear, although I don't understand how such a mechanism would be restrained, what happens if the housing spins? and if it is a press fit then it's not exactly easy to adjust anymore?

The pivot point is 640mm behind the axle line, I will show more pictures tomorrow so you can see more of what is happening underneath the car.

Kevin, thanks for your input, I was hoping I'd hear your thoughts on this at some point! :) Interesting to know how much adjustment you had given the similar rear setups, did you have any issues with movement of the shims? Thanks for the compliment though, hopefully it will all come together well.

I was hoping to have all my design work done by Christmas but it looks like I'll be overrunning slightly unless I can get all of this sorted over the next few days which is doubtful.

Christian

mech5496

12-22-2014, 10:46 PM

Z's link was the one I was talking about a couple of posts earlier. Consider that camber adjustment method would be better to be done by replacing something solid (i.e. shims) rather than using some sort of slider, as loads are high and you want to avoid compliances as much as possible. Kev I had a short talk to some of the team at UK which mentioned that camber and caster are shim adjustable. How you guys cope with mounting holes/bots misalignment though? Slightly overbore holes and call it a day?

Claude Rouelle

12-23-2014, 05:34 AM

Just as simple steady state consideration.

If you reduce your mass 10 % and lower your CG 10 % you can reduce your tracks 20 % and keep the car from rolling over with the same lateral acceleration. And that is without any downforce.

But have a look at the difference in yaw inertia.....

Remember to calculate the yaw inertia of your 4 suspended masses around the CG (parallel axis theorem) and compare it with your engine (even a 4 cylinders) Vs CG yaw inertia: you will be surprised.

In transient things are not going to be as simple calculations but you will not be far away anyway.

12-24-2014, 11:05 PM

If you reduce your mass 10 % and lower your CG 10 % you can reduce your tracks 20 % and keep the car from rolling over with the same lateral acceleration. And that is without any downforce.

Claude,

20%!!!???

Ooops!!! I hope that is a typo!
~~~~~o0o~~~~~

Christian,

"... so the only way to do it would be to remove the upper link entirely and replace the lower link with a much thicker [and tapered] one." <- Yes!
~o0o~

"It would probably be necessary to fabricate some gusseting between this and the upper attachment point too,..." <- Not really.

The upright's upper-BJ carries relatively much SMALLER loads than the lower-BJ. The structure from the main beam about 200 mm inboard of the wheel (ie. roughly where the SD attaches, and the area that should be the strongest section of the beam) should taper slightly towards the upright's heavily-loaded lower-BJ. Roughly half way along this "limb" there should be another limb "branching-off" upwards, and tapering even more to the lightly-loaded upper-BJ.

Visualise where the big, medium, and small forces are acting, and then try to imagine how a tree's branches would grow if they had to carry these forces.
~o0o~

"I'm just concerned I'd be placing a considerable bending load (pretty much the entire braking torque) on the attachment between the beam and the arm." <- Yes!

But that is fine. It WILL work. Remember that the braking and cornering forces originate at the tyreprints (ie. at ground level) and are then reacted MOSTLY at the beam's main apex-BJ, and also at the SD BJs. These forces take a little detour up through the wheel structure, and then through the wheel-bearings, but for the most part they can travel close to the ground. So mostly on a line from tyreprint to apex-BJ.
~o0o~

"I like the idea for the rear, although I don't understand how such a mechanism would be restrained, what happens if the housing spins? and if it is a press fit then it's not exactly easy to adjust anymore?"

Several options, but one is to have the outer housing split like a "C". Two biggish bolts (eg. M8 or M10) bridge the gap in the "C" and clamp it tight on the inner sleeve. It is only the tiny frictional-force from the ball-bearings that will cause any spinning, so no problems there. But tyre Fy cornering loads will push the sleeve axially towards the diff, so best to have a larger OD shoulder on the outboard side of the sleeve, to prevent it sliding inwards through the outer C-tube.

Note that this sort of adjustment only works for INBOARD-brakes! For outboard-brakes any Camber and Toe adjustments should also move the calipers. Or else you might be able to re-adjust the calipers to suit the new disc position whenever C&T are changed?
~o0o~

Edit: In your rear-CAD-view last page, you can move the SD's lower-BJs downwards, so the SDs point directly at the centre of the wheelprint. This is better, structurally and kinematically, IMO.
~o0o~

I will try to do a few sketches of above stuff over the holiday break...

Z

Claude Rouelle

12-29-2014, 10:28 PM

~~~~~o0o~~~~~

Car of 200 Kg in a simplified 2D mass. That is 100 kg or a force of 981 N per wheel
CG height 300 mm
Track 1200
Lateral acceleration needed to get the inside wheel load to zero is 2.00000001 G

~o0o~

Let’s get 10 % of the mass and 10 % of the CG height
Car of 180 Kg. That is 90 kg or a force of 882.9 N per wheel
CG height 270 mm
Track 1080 (which is -10%)
Lateral acceleration needed to get the inside wheel load to zero is 2.00000001 G

~o0o~

So there was effectively a typo in my last December 23rd post. Apologies to all.

~~~~~o0o~~~~~

Ahmad Rezq

12-30-2014, 05:40 PM

For the braking system,

Defining the braking system variables is a good start in order to proper design the system,
I will assume that you set your static weight distribution, your wheel base, and have a good estimation of your cg height.
Starting form vehicle dynamics equations you can figure out the braking force distribution between front and rear.
Baking to the braking system, to proper size the hydraulic system components we need to first investigate the system parameters.
1 - The driver force
2 - The Balance bar ratio ( Assuming Balance Bar system is used )
3 - The MC/s Bores size
4 - System Pressure ( Assuming Ideal Analysis )
5 - Calipers pistons size and number of pistons
6 - Calipers pads mu
7 - Front and rear rotor size.

Here are my tips that i used to design the braking system
1 - I did choose my front and rear calipers considering their bore size , number op pistons , weight ( Unsprung mass ).
2 - I make initial sizing for the rotors considering the calipers size , wheel package
3 - Assume initial pedal ratio and i will talk about it later
4 - For the rest of system parameters and knowing the braking force distribution at the maximum deceleration i did iterations considering the following:
I iterate many configuration of master cylinders bores with the selected calipers and the results were :
MC/Front - MC/Rear - Bias Ratio - Driver Force To Lock The wheels

there were many combinations and i filtered the results based on the following
1 - The bias ratio is 50/50 or closer
2 - The driver force is not too small or not too large

Pedal ratio :
first we assume an initial number for the pedal ratio to start the iterations and we need now to optimize the pedal ratio
the proper pedal ratio is that to give the driver better feeling of the braking system
In FSAE one must consider the braking test 2000 N on the braking pedal you may design your system with a very high pedal ratio but this won't help you in the braking test ie ( Increasing pedal bending , and pressure which may lead to line failure or worst ) .

For the braking system i designed and after choose the proper combination as mentioned i made small iteration on pedal ratio i tried to reduce it and compromise with driver force to lock the wheel.

you need also to check the pressure in order to design your lines also check it with your parts suppliers.

Here's a snapshot from the iterations done on a car with following specs

Car specs

m_car+m_driver = 255 kg
wheel base = 1550 mm
Static weight distribution = 50-50%
Cg Height = 250 mm
wheels = 10'

Max dec = 1.5g

Selected parameters
1 - Front and rear calipers bores = 25.4 mm with 2 pistons
2 - Rotor size Front and rear [Outer Dia , Inner Dia]=[175,125]mm
3 - Pedal Ratio = 5

464

Claude Rouelle

12-30-2014, 07:50 PM

Ahmad,

What is your goal here? if it is to design and simulate a complete braking system I feel a few essentials things are missing: basic coefficient of friction of the brake pad on the brake disc and on the tire on the ground, compliance sources and measurements, acceptable brake pedal travel, conversion of the vehicle’s kinetic energy into heat energy and dissipation calculation, initial brake disc temperature and calculation of brake disc temperature at the end of the braking phase, moment of inertia of rotating parts, initial and final braking speed, brake disc volume, specific mass and mass and brake disc material specific heat, contribution of the braking of the engine downshifting, estimation of the brake temperature on a complete lap, time (or number of laps) it takes to reach the nominal brake temperature window .....

Still way to go my friend.

Ahmad Rezq

12-31-2014, 03:21 AM

Cloude,
For sure you are right
My goal here is to initially size the hydraulic system, setting the pedal ratio and initially setting the rotor geometry. As you mentioned there are many things to do to complete the whole system design,
System Volume Analysis.
System Thermal Analysis
Etc.
So don't take my comment as the complete view of the braking system design as it's not and i didn't mean it to be

ChristianChalliner

01-07-2015, 05:48 PM

Just a quick note to say thank you for the comments over the holidays :)

We have our January exams soon so I will probably not add too much to this until the end of those.

I do have one question for Claude though,

You say calculate the yaw inertia for the 4 suspended masses about the CoG it sounds silly but I don't really understand what you mean here when you say 4 suspended masses, to what are you referring here? Are we talking the individual corner weights (vertical loads) acting at each contact patch or something else?

Also, the comments on the braking system are useful but perhaps for a following year, it really isn't supposed to be my area so I can't dedicate as much time to it as I would like with regards to things like thermal analysis of rotors and brake fade.

Thanks,

Christian

mech5496

01-11-2015, 03:52 PM

You say calculate the yaw inertia for the 4 suspended masses about the CoG it sounds silly but I don't really understand what you mean here when you say 4 suspended masses, to what are you referring here?

I believe what Claude means is how much yaw inertia all four corner assemblies (wheels/brakes/uprights/hubs etc. AND beams) contribute to the total car yaw inertia (MoI/z)

ChristianChalliner

01-11-2015, 08:37 PM

Ahhh ok! I assumed it was along those lines, just i was thrown off by the term 'suspended' for some reason, essentially we're talking about how much the unsprung mass contributes here then.

01-11-2015, 08:44 PM

Christian,

Some new stuff on the Beam-Axle thread that you may be interested in...

But STUDY FOR EXAMS FIRST! :)

Z

ChristianChalliner

02-12-2015, 06:17 AM

Hi guys, big update coming on this shortly. Things not progressing smoothly though :(

ChassisSim

02-18-2015, 09:44 PM

Hey Guys,

I posted this on the Dan's Vehicle Dynamics corner thread a couple of months ago. However having a read of this thread I think the following is very appropriate to be shared here,

http://www.chassissim.com/blog/chassissim-news/using-chassissim-to-design-a-race-car

It's about how to use simulation (ChassisSim in particular) in the racecar design process. It's focused on how ChassisSim has been used in the past for racecar design projects.

Forgive me in advance if this is a repost on this thread. I was talking to a few of my colleagues last week and they found this really useful. I trust everyone else will get a lot out of it.

All the Best

Danny Nowlan
Director
ChassisSim Technologies

ChristianChalliner

03-05-2015, 07:06 PM

Thanks Danny, I've been watching a lot of your vehicle dynamics corner videos and they help out a lot, they're also pretty good when it comes to finding simple ways to explain concepts to other team members so thank you for providing those to us.

With regards to the project, where to start really. Bad to worse to worse than bad to maybe we'll be ok in the end has been my feelings on this really.

Essentially, the decision was made by the faculty adviser that the beam axle concept would not be feasible this year and that also a management reshuffle was necessary. I was disappointed to say the least but I can see the reasoning and despite having the option to pursue a rear beam axle only car I decided that it did not fall within my original concept and that I did not like the idea of having to run a bump compromised front end with stiff springing as I felt it removed some of the key gains of running front and rear beams. You might disagree but that was my feelings on the situation.

As such, shown below is as far as our beam axle concept will go, which is a great shame. Myself and other team members don't want our work to go to waste on this though and have decided that at the projects conclusion (end of exam season) we will post all the information and related items for the beam axle concept here, this will include all CAD, all spreadsheets, probably a few team members dissertations and some extra thoughts. We believe strongly that this concept can work and that it should be pursued by someone with the flexibility and desire to do so.

http://i1296.photobucket.com/albums/ag13/challicm/FSAE%201_zpsk0nzamhy.jpg

http://i1296.photobucket.com/albums/ag13/challicm/FSAE%202_zpsamksbird.jpg

The other news is that in the reshuffle I was made the team manager, which is not a roll I wanted, certainly not at this stage in the project as it seems it's basically been dropped on me at a point where we've had to perform a complete redesign in less than half the time with very little chance of succeeding.

So, our new car, it's a double-wishbone car. It's reasonably standard fair but carries over a few things from our previous design such as the pedal box, diff hanger, interior concept, some frame design and the shocks. Practically the only thing that isn't carried over is the suspension concept. Given the haste that this has been put together with there are numerous deficiencies with the design but ones which we consider acceptable compromise given the situation. For example, the VSAL lengths are equal to track width, the honesty of this is that without data and with only the very basic optimum lap sims I did near the start of the year it's difficult to get much further so we decided that this would be a good datum point to start from. Similarly, the front roll center is at ground level with the rear 30mm higher, the reasoning? ground seems a good place to start when you have no idea otherwise and 30mm higher at the rear is more by convention than anything else.

Anyhow, here's the car, see what you think, rip it apart, you've all helped us a great deal so far and we need your support more than ever right now.

http://i1296.photobucket.com/albums/ag13/challicm/FSAE%204_zpsazyji0ly.jpg

http://i1296.photobucket.com/albums/ag13/challicm/FSAE%205_zpsgmoshbpu.jpg

One thing which concerns me the most is that our rear uprights are a carry over part which are known to have issues. Fortunately the upper and lower points are removable on these so I'm going to do my best to make use of the main body and reduce the scrub radius and increase the size of the toe base as much as possible. It might even be possible to machine new bodies if we have the time but it looks unlikely.

In terms of stats, this frame is 3kg heavier than the beam axle car but the suspension weighs approx 7kg less so it may be lighter overall.

We've started manufacturing the frame this week and are currently about half way through profiling all the tubes, we expect to have these finished by tomorrow, after that it's onto the jig.

Oh and, the entire new car was designed in only 3 days so, there's likely a lot of things we've missed so please, call a spade a spade if you see anything majorly wrong!

Thanks,

Christian

CWA

03-05-2015, 07:44 PM

Hi Christian,

Reading between the lines of the technical details you've posted, I see you've conveyed many feelings that I recognise as having had during my first year of real FSAE involvement. I just wanted to say best of luck to you over the next few months, even when it feels like the plan is falling apart, stick with it, being able to adapt to big changes at short notice always requires strong character.

This isn't the only car you'll ever build! So don't be disappointed when external influences or factors deemed out of your control act to change things this time around. There is always next time. Things like this happen in industry too, even if perhaps for different reasons. Don't get too hung up on how the car has had to change at such a high level, nor how this has altered all the design metrics you considered to be important over the last few months.

Recover what you can, but now make sure you are properly focused on the build and make sure efficiency of delivery is prioritized. Make your peace with how the project has turned out so far and carry on, make sure your team feels this way too. It's easy for members to lose interest and direction in times like this, so stay confident and positive. Now that you're team leader you are responsible for keeping your team strong, do this by setting a good example. If you can do this well, you'll feel the reward when the real crunches come.

I look forward to seeing your car in the summer.

Jay Lawrence

03-05-2015, 09:35 PM

Christian,

Nothing like an engineering project run by politicians eh!
I would second what CWA said in that you just need to make it work now. We had a similar issue in 2009 where the car was going to use a hydraulic interconnected suspension system; it wasn't managed properly and failed miserably right at the installation stage, so a junior member and myself (as powertrain leader with very little suspension knowledge) had to get a conventional system working. We put our heads down and built the car with about 6 weeks of tuning time (not enough, but more than most) and finished 3rd at FSAE-A that year. The point is, just get on with what you've got, and if you complete it early enough you can fix whatever doesn't work in time for comp.

Also just to add: if you are hanging around next year, don't give up on your concept. Keep it going in the background so that after comp you can go further with it and get the details sorted for early implementation next season.

Ahmad Rezq

03-06-2015, 12:12 PM

ChristianChalliner,
Sorry for not reading many of the entire comments here, but when looking at the images you posted i had some questions
1 - what is the Torsional stiffness for your chassis ?
2 - what is the center distance between your sprockets
3 - what is your final reduction ratio ?

Claude Rouelle

03-06-2015, 01:10 PM

Ahmad,

Why do you need to know the answer to the last 3 questions you asked to Christian?

Let's say Christian gives you these numbers, how useful would that be to you and your project?

Don't you think that a better question would be to ask why and how Christian came with the numbers he has (whether he gives them to you or not) and first YOU to give the reason why YOU think these numbers are important.

That approach would be more in the spirit of this forum, don't you think?

And the answers and information you will get from Christian and others will be even more useful.

But that would requires a bit more lines to type in your email and maybe a bit more risk taking by exposing how much you do not know?

But aren't we all the same? At the certain time we all realize how little we know compared to how much we should know.

Be humble, be risky. Dare to question the knowledge and the establish "principles" of everybody including the "experts".

And never stop using the word WHY.

Ahmad Rezq

03-06-2015, 01:25 PM

Claude,
I appreciate your contributions in teaching the new generations to introduce their selves before posting or to include the reasons for every question they asked and more which we must respect you for.
any way i asked these questions and waiting for Christian answers to discuss about some issues we faced in car design.
:)

Claude Rouelle

03-06-2015, 01:35 PM

Then Ahmad say it so and include these questions in your thread instead of just asking for numbers!

How would you react if somebody would bluntly asked you where your roll centers are, what Ackermann you use and and what your weight distribution is without asking the reasons why they ask these questions or explaining the challenges they face?

It is just a matter of simple communication skills to imagine how the reader is going to react to your rather terse questions before you post them.

Ahmad Rezq

03-06-2015, 01:47 PM

Claude Rouelle
I wouldn't mind provide him with the numbers he asked for. believe me this answer is not because i asked the same way.
it depends on the manner Claude, you can ask but you can't order. i didn't force Chris to provide me with the data.
we may lost as we are using keyboards to transfer our thoughts.
I wish you could change your look in many posts here in the forum and take it simple and easy as we all here wanna gain from your knowledge.

Claude Rouelle

03-06-2015, 01:49 PM

From my knowledge a bit and from others a lot

Ahmad Rezq

03-06-2015, 01:59 PM

Claude Rouelle
Indian people drink hot milk.
we are here from different cultures and that doesn't mean at all to consider the forum or any mean of communication like a supermarket, but we may have different thoughts especially in communication and i think you as an international instructor knows this very well.

Claude Rouelle

03-06-2015, 03:01 PM

And you do not need to make excuses about it.

I am just trying to help you with the general way people communicate in this forum and in the industry.

Remember that what triggered my remarks was the blunt question you asked about somebody else numbers (without anymore comments about the whys and the hows of your questions) and that in my opinion is not acceptable wherever you are from.

It goes against the learning process in general and the fair spirit of this forum in particular.

Yes there are different cultures but there are also some common language and common sense habits (introducing yourself, making the effort to explain what you already know / don't know / understand / don't understand / have already tried or not are some of them) to use if you want efficient communication and collaboration.

From my perspective of a design judge and as a the teacher, you will not stop me voicing my opinion on the need of communication improvements that some students have, again, wherever they are from.

Ahmad Rezq

03-06-2015, 03:37 PM

Claude
Be sure that your message is received
Thanks (Y)

Claude Rouelle

03-06-2015, 03:49 PM

I guess you meant message. Again it is all about common codes in communication and language ...

Tough I wonder what a Egyptian massage is .... :)

ChristianChalliner

03-06-2015, 04:10 PM

I have no problem admitting how much I don't know :p , it does scare me a little sometimes and makes me realise I know just a fraction of what I would like to know. At the same time though it's exciting, to know there's still so much more to learn is a great thing, as long as you can keep the enthusiam for it then it's a lot of fun.

I was immensely disappointed when I was told that we wouldn't be carrying on the beam concept (i seriously thought about quitting the project) but after maybe a day of messing around with a double wishbone car I started to have fun again and the optimism was back.

There's no point in giving up when there's still the chance to do well, we finished cutting all of our chassis tubes today, the method we used to create the profiles was much more effective than I expected, we used SolidWorks to produce a paper profile of each end before wrapping it around the tube, once we did that we marked up to the edge of the profile and hand filed to the edge, we have around 50 tubes and we completed all of them over two days. We made an instruction booklet on how to make the tube profiles on solidworks so I'll upload that if there's interest.

With regards to the questions, Claude, I'm sure there's many many areas you could choose to tear apart if you wished and I would really like it if you did as I'm sure I'd learn from it and it's good preperation for design.

To answer the three questions Ahmad, 1. Torsional stiffness - I do not know I will ask our chassis guy but I will say this, you'd be surprised how much you gain by exchanging one member for two and how little this impacts upon the weight. 2. Center - center distance is very small and a concern, I don't know the exact number but I know it is pretty much on the limit for the amount of chain engaged on the engine sprocket and you should consider other chain designs than the norm if this is a problem but it is solveable. 3- hmm, if i remember correctly the driveline guy wanted to use a 17 for the engine sprocket? And a 42 for the diff which gives 2.47? I'll quiz him as to why on monday.

Thanks,

Christian

As an extra thought, the Nissan LMP. It gives me hope there's still creativity left in the world, I'd love to have worked/work on that project.

Claude Rouelle

03-06-2015, 04:21 PM

Christian,

2 questions

1. Why was your beam axle idea rejected? By who?

2. Have you ever consider the difference in compliance (at equal weight and good use of best design practice and FEA tools) of a beam axle compared of a double wishbone on both the suspension elements and the chassis?

ChristianChalliner

03-06-2015, 04:45 PM

Claude,

1. It was rejected because of time and because it was becoming 'too complicated' the academics did not believe my proofs of the stresses in the front beam because (and I mean no disrespect) they did not understand how it functioned with its lateral and longitudinal restraints. In terms of complication the steering of the front is particularly tricky, in some ways preventing bump steer in a purely straight line situation is easy, in a roll situation not so.

Because the column running to the pitman arm on the floor could not flex laterally it resulted in around 0.3deg of roll understeer per degree, I did not consider this too much of a problem because, well, you just turn the wheel more. Others did consider this a problem.

There was also other problems like the use of conventional uprights as opposed to something like Z's tractor kingpins created an interferance issue with the steer arms unless the assembly was moved forwards in the car, this reduced the ackermann we were able to achieve and also put a not insignifcant mass further towards the front of the car. Similarly, the gearbox itself is a heavy component placed high up, not good for CofG but somewhat offset by the beams placing a lot of weight down low.

The biggest killer though was the realisation that we would need 3 jigs (2 for the beams plus a chassi jig) and all would have to be jigged in conjunction with each other, this was considered to be extremely time consuming and undesireable. Likewise the fabrication for the beams themselves was considered to be 'too difficult' despite the fact I did variations in every conceivable manner (bent tube, folded, fabricated from box, etc) it was always 'too difficult'.

This combined with the pressing time (we are over two months behind schedule) in short became too much, a lack of faith in my ability allied to a lack of desire to make my design (I was pretty much questioned at every turn about "why can't we just do double wish" from all corners, team, faculty, fabricators) led me to just buckle in the end and give in to the demand to revert to a double-wishbone system.

In essence they just did not want it regardless of the reasoning.

2. Not in as much detail as you mentioned but certainly, the 'point' loads inflicted in the beam chassis by the restraining mechanisms are large in comparison to how the double wish spreads the load out. Considering the weight of the beams I'd say it's conceivable to say that it's possible to have a stiffer double wishbone car for the same weight BUT, is it necessary? i can't answer that because I have no past experience of either.

Ahmad Rezq

03-06-2015, 06:08 PM

Claude Rouelle
it was written wrong as i'am not that good in English.

Ahmad Rezq

03-06-2015, 06:25 PM

Chris i think you will need to add another support in side impact .

510

our center distance is narrow about 200 mm with a final gear ratio = 3.6 using a 10 teeth to 36 that scares me a little bit.
but Chris did you check the 2.6 on for example optimum lap as i think you may not have the proper torque to accelerate the car.

Claude
Chris a person from United Kingdom took my words in a simple way and provide me with the answers without making a joke of my keyboard mistakes :) .

ChristianChalliner

03-06-2015, 06:49 PM

Ahmad that's the beam axle car you've drawn the bar in which in our opinion didn't need the extra stiffness. The chassis guy also thinks similar for the double wishbone car but we'll see.

If i'm honest the final drive is from memory, i will check it on monday with the driveline guy, i do agree the number seems a little low but the cbr is quite a powerful and torquey unit so in our opinion it's unnecessary to be banging through the gears all the time. Our engine guy has also been working on improving the low end torque to allow us to do this. If you look ECU's car only has two gears and was rapid in acceleration at aus 2014 so...

Ahmad Rezq

03-06-2015, 07:21 PM

aha sorry for that seems like i went wrong when downloading your images but i saw both cars and meant the car with double wishbones

for final gear ratio i think and especially at this time due to the narrow center distance you will suffer if you increase the sprocket size, we went for this problem and it was painful and we still scare from the situation with the current assembly being manufactured.

ChristianChalliner

03-06-2015, 07:28 PM

Well your engine sprocket is only a 10 tooth so that's going to result in rather minimal chain engagement, I think to be honest you have it worse than us in that respect. According to the chain manufacturer we use they recommemd something like 120 degrees of engagement minimum if i remember correctly but i did read that a long long time ago so don't quote me on that. I also think we're running pretty close to that.

03-06-2015, 11:49 PM

Christian,

BE HAPPY. You have just passed through one of those magical "rites of passage", and you are now living in the real world of (ughhh...) clever and reasonable "grown ups"! :)

More seriously, I echo what CWA said back on page 15. You have just been bowled one of the many googlies that life will throw at you. I find that growling at the dog, kicking inanimate objects, and generally moping for a day or two is good medicine. And then thinking about how to make the best of what is in front of you. You seem to already be doing this, by thinking about Double-Wishbones. So, ALL GOOD! :)
~o0o~

With regard to the switch from Beams to DWs, do NOT worry too much. Although I am one of the main promoters of Beams on this Forum, I try to stress the even more important point that specific suspension type is NOT a major performance factor in these smooth-track FS competitions. As per the old saying (usually attributed to Colin Chapman), "Any suspension will work, if you don't let it.". That is, in worst case you just fit "rigid" springs to your DW car and it will perform like a go-kart ... which can be very fast!

More important than the specific suspension type is the execution of its details. Most important here is "enough" reliability to finish, followed closely by "enough" toe-stiffness to be driveable, especially at rear. Best way to figure out how much is "enough" is to finish build early, then test mercilessly! Follow with strengthening and stiffening as needed. Final paint job as late as possible.

To put further gloss on your predicament, by the time this is all finished you will be TWICE as knowledgable about suspension design. You will certainly have a lot to talk about in the Design tent, with your initial preference for the superior Camber behaviour of Beams, but then the necessary compromises you had to make because of the forced adoption of the more complicated DW design. Ahh..., "market-pressures", etc...
~o0o~

With regard to your higher-ups' views on "complicated and difficult" design, I have found that the best approach is to tell them as little as possible, and just get on with building it. Sounds difficult, but it can work.

"Well, Mr Supervisor sir, thank you for your very helpful advice about the unnecessary complication of my design. I am finding that advice fascinating ... because here is a prototype I knocked up yesterday afternoon. I guess I must have made some massive mistakes, because for some reason it all came together very easily. Not sure where I went wrong??? Anyway, the preliminary compliance testing I did showed that it has at least FIVE times the toe-stiffness of last year's design. So, err..., I'm baffled. What should I do, sir?"

OK, my diplomacy skills are crap. The above will only turn Mr Supervisor's face bright red, with that big vein on his forehead about to pop. And too late for changes now, anyway.

(But, BTW, I recall Kevin mentioning how easily their folded-sheet-steel rear-beam came together for the 2014 comps. Out of curiosity, anyone from ECU care to comment on just how "complicated and difficult" they found this design?)

Once again, best is to get on with finishing the DW build, then on to testing. As has been said before on this Forum, you might not be able to turn a pig into a racehorse, but you can surely make a mighty fast pig. Remember that Colin Chapman, et al, started out by hotting-up Austin Sevens!
~o0o~

As a final recommendation to both Christian and any other newish FSers, read Superfast Matt McCoy's (http://www.fsae.com/forums/showthread.php?7163-Searching-for-the-limit) take on this whole adventure. His book is now available for Free Download here (http://www.superfastmatt.com/2012/01/free-racecars.html).

Three good reasons for spending the day or two it takes to read it:
1. Very well written!
2. Shows that progress in the real world is rarely straightforward. Instead, mostly twisting, turning, rocky roads, that are always darkest before dawn...
3. A future reminder that the stuff you are doing now may well be the best time of your lives!

Z

(PS. I would have the front-SD-top-BJ mounted to the FRH-to-upper-SIS node (= same as upper-wishbone-rear-leg-frame-BJ), to save one node and one tube. But this is only a tiny detail...)

ChristianChalliner

03-07-2015, 08:16 AM

Z, that's what everyone tells me, that I've just learnt something sooner than I would have otherwise. Yeah what you say is pretty much what happened, I announced my displeasure with the situation, argued, disappeared for a day or two and then decided to make the best of what we've got.

That's the plan on the suspension, if it works great, if not, I've got some super stiff springs lined up to help go-kart the thing up, I'm hoping it wont come to that though!

One thing I did forget to mention was that the rear RC/ front RC offset wasn't entirely a convention based decision, what I actually wanted to achieve with that was to give a helping hand in lifting the inside rear wheel so I can bin that Drexler diff and throw a spool in there. But I struggle with the maths behind it so generating a number which gives me that is difficult / I'm not confident on my answer.

Toe stiffness has been a primary consideration, both front and rear have large(ish) toe bases, 110mm rear, 80mm front (front is limited by slow speed rack).

You're probably right in telling them as little as possible, I made the opposite mistake, I tried to explain the entire system to them including built models which showed how it worked and the like but it didn't pay off. I lost it a few times which probably didn't help matters, there was a specific incident where I proposed two designs for front beams whereby one solved an issue of the other but was slightly more difficult to make and it ended with me saying "you gave me a problem, I solved it, what do you want me to do?!". I should probably work on that...

The aim now though is to just get some starting points for the DW car, it's probably not optimum but at least the starting points give somewhere to go from next year and onwards and start from easy to understand places, in my opinion if someone sees a VSAL length which is equal to track width it's much easier for them to then decide "ok so we probably want it a bit shorter, maybe 0.9 track width" than it is for them to go "well last year it was 937.325mm, I think we should move to urhmmm, 923.52mm!" but that's just my opinion on these things. Likewise, with the roll center heights, by rights there can't be jacking problems that are roll center related at the front because it's ground level so if there are then someone needs to point the figure at caster + spindle + offset, etc.

You raise a good point about the shock mount! I wish I'd thought of that now, annoyingly, I did at the back but not at the front, hmm, it might still be possible to do that since we haven't started welding up yet.

As a final point, I started reading Matt's book, in the first few pages it conveyed much of how I've felt moving through this project so I'd recommend it, also, check out his blog and his big bore Suzuki guide, that's got to be one of the funniest engine tear downs and rebuilds I've read!

Thanks,

Christian

mech5496

03-07-2015, 11:50 AM

Christian, I believe Mitchell posted a picture of the 2015 UQ concept rear beam in the "beam axle" thread, I think you cannot possibly build anything simpler than that! Anyway, I know people higher up changing your concept just because, and I have found that the best possible reaction is to face it and go from there! Really eager how you guys will do in the next few years, and please stay with the team, you are the kind of engineer/person that is needed in FSAE!

A bit offtopic, but Matts' book is great indeed, so great that I recommend buying a hard copy to all FSAEers.

ChristianChalliner

03-07-2015, 01:20 PM

I saw that, There's a picture of the back of the car on their facebook page, looks very similar to what we planned to do so i'm really keen to see how it turns out!

I think you could make it simpler, I'd drop the wheel hubs for a start, I see/know why teams do them but I don't like them, it makes you locked into the wheel you put on it unless you want to remachine the stub axle which in those cases looks time consuming, I also don't think it fits with a weekend racer ethos but that's just my thinking on it.

Me staying on isn't really my choice, the project is run for third year students so anyone else that is around is really only there by choice and if the next team decide they don't want me around I can't say no.

Jay Lawrence

03-08-2015, 11:37 PM

The project is run (only ?) for 3rd year students? That's a fantastic way to fail every damn time haha. If you're passionate about it I'd stick around, it certainly puts one ahead of the game for future endeavours, and you might even start a trend of people persevering with it even if it doesn't directly benefit their uni marks (as was/is the case with mine and many other unis).

ChristianChalliner

03-17-2015, 07:12 AM

We have mentioned this yes but it is unfortunately the way it has always run. Realistically, it should run as everyone else runs (society based) but it's not that simple to get through the transition period to that system as we found out this year.

I think to be honest the biggest problem is always ego which will continue to be a problem. The reason is that whilst it runs as a third year project it's difficult to get others on board and even when they are on board there is inevitably friction as one group of students is being marked whilst the other is not.

It seems to create a sense of entitlement for those being marked and similarly, a sense of under appreciation for those not being marked which is never going to end well.

Anyway, irrespective of the above, our current progress is this:

All chassis tubes are cut, a prototype pedal box was plasma cut this morning which i need to take a look at, we're in the process of designing the jig which should hopefully be completed either today or tomorrow so that we can order material and start building that next week.

With regards to other components we've made the decision to use steel A arms in order to save time and i've designed what I think is a reasonably quick jigging method for all the wishbones (will post pictures later). I was particularly interested in Z's suggestion of non-over constrained wishbones which I looked into but decided against since there are more operations required and time is at a premium, maybe next year?

The steering wheel and dashboard are pretty much complete now.

Lots still to do like:
Uprights
Diff hanger
Weld chassis
Intake (to be 3d printed)
Exhaust (made outside to a student design)
Dampers to finalise ordering
Springs to order
Arms to make
Pedal box to make

Basically a whole car still. There's more to say so i'll be back later with more information on things :)