Vehicle Dynamics starting points and design process

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

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

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.

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

Quote:

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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...)

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:

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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.

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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'.

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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'.

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.

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.

Christian,

More BLUNTNESS follows...

Quote:

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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'.

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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~

Quote:

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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.

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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

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 ;)

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 :)

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.

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

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).

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/...994_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.

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/8045...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 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

Christian,

Vehicle Dynamics and CAD are not necessarily the same coordinates

But OK now we have erased a communication issue. Good

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/...ps87f4738c.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/...ps36ee34ae.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/...ps7ac0d560.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...

Quote:

---

Originally Posted by ChristianChalliner

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.

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.

Quote:

---

Originally Posted by ChristianChalliner

http://i1296.photobucket.com/albums/...ps36ee34ae.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/im...107_rechts.jpg

Quote:

---

Originally Posted by ChristianChalliner

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". :)

Quote:

---

.. 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...!!! :))

Quote:

---

Originally Posted by Z

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

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/...psd38a3295.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.

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. 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.

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/...psd38a3295.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

Quote:

---

Originally Posted by ChristianChalliner

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.

---

Composites? I did only mention them because they are quite obviously visible in the picture, and I know Z's opinion about the use of them. :)
Difficulty of an elegant solution for sitting the mounts on (conventional, not CF) chassis nodes? Rocker mount at/near rear lower A-arm node, damper top mount = bottom of front hoop.

Quote:

---

Originally Posted by Z

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!

---

I did, don't worry! ;)
And concerning the brown go-kart and undertray... I joined my team in 2007, and although I am not a member anymore for quite a period of time, I still visit the (new) guys quite often. Being very interested in aerodynamics, I did mention the importance of an undertray first in 2007. And from then on every year. Together with suggestions that a double A-arm suspension might not be the be all and end all of everything. But, you know, I am an engine guy. So, naturally, the suspension and aerodynamics team know it very much better, and well... F1 has double A-arms and a tiny diffusor, the racecar book tells mainly about double A-arms and wings, so this has to be good.
We might disagree on our choice of engines, however...

And finishing a car precisely at xx o'clock... Well, xx o'clock exactly. Plus a month or two, like the rest of the world ;)

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/...psyg9mt5vx.jpg

http://i1296.photobucket.com/albums/...psaapbuynl.jpg

http://i1296.photobucket.com/albums/...pswrdudua6.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/...psecd7848a.png

http://i1296.photobucket.com/albums/...psb1ef8689.png

http://i1296.photobucket.com/albums/...ps547b3cab.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.

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.
Attachment 398

And the completed rear end for comparison.
Attachment 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.

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

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/...psxpucqd6z.jpg (Sorry about the picture).

Quote:

---

Originally Posted by ChristianChalliner

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) ;)

Quote:

---

Originally Posted by ChristianChalliner

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.
Attachment 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.

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 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

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/...psfhwpd73b.jpg

Which removes the excessive length of this current one

http://i1296.photobucket.com/albums/...ps2ikcrkgd.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.

Quote:

---

Originally Posted by ChristianChalliner

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! :)

Quote:

---

Originally Posted by ChristianChalliner

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.

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" 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. 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

Quote:

---

Originally Posted by ChristianChalliner

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.

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...

---

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. This analysis was done with a nice simple parallel axis theorem, and was accurate enough for us to make high level decisions with. We then refined the angle when we had more parts placed in the frame and had a better idea of how much space we had/needed.

As for the deliverables, you may be able to point out that there is nobody in your list that is focusing on the big picture VD for your team, and that as such, you are working on that. If that doesn't work, maybe link whoever you report to to Geoff's "Reasoning" thread and have them read that?

-Matt

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Originally Posted by ChristianChalliner;121709Mitchell - 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?

We also had this idea for a pedalbox...

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

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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.

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).

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.