Just thought you might like a source for some steering components and ideas:
http://www.hyperracing.com/pages/pro...category=12500
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Just thought you might like a source for some steering components and ideas:
http://www.hyperracing.com/pages/pro...category=12500
With these calipers it is highly likely that there is air in the system somewhere as they're next to impossible to properly bleed. The only reliable way I found after days of trying was to run brake fluid from a pressurized container (read: coke bottle...) through the system with the caliper in my hand and slowly turning it over while the fluid is "running" through. There is one place in the caliper where air will almost certainly be trapped if you don't move/rotate the caliper while bleeding.Quote:
Originally Posted by ChristianChalliner
Hi everyone,
Luniz, Mitchell thank you for the link and also for the advice on the caliper, a few years ago there was a part machined where someone tried to link the two line inputs on the caliper to each other in order to remove the T-piece connector in the lines, I'm not really sure what happened other than I was told it didn't work particularly well, I can only assume that what had effectively happened was that the connector had been screwed into the adapter such that there was no fluid flow to the upper caliper pot. Personally, I think it's worth doing properly again at some point but needs the proper research and testing carried out as running a line splitter hovering in free air doesn't look particularly nice or fill me with great confidence.
I'm sorry it's taken so long to update this with any real information, there were a few issues last week which prevented me from doing any significant work however, I do have a rough CAD drawing for you all to look over/criticize/etc:
http://i1296.photobucket.com/albums/...ps17aeadd5.png
So a quick rundown. We've decided that we would like to do a front and rear beam, the reasoning behind this is that a rear beam has been proven to work effectively and package very well (certainly in the case of ECU and UQR), we'd also like to do a front beam as running through the manufacturing we reckon we can build one much faster than last years double wish setup. Another reason is that looking at UQR's car it looks like they are running very short FVSAL's to give similar camber gain in roll at the front to their rear beam. In our opinion this compromises the chassis at the front end as it forces you to place either the upper arm attachment points in the middle of a bar or the use of more bars to triangulate the points whilst still meeting the frame rules.
Another main aim of ours is to reduce the frame weight by at least half, using a front beam allows us to remove even more bars from the chassis and also removes the need for the chassis to have sufficient stiffness to prevent camber compliance issues, we fully accept that it does NOT remove the need for the chassis to control the axles to prevent them wandering left/right and likewise that the beam then must have sufficient stiffness to keep camber compliance to a minimum.
Both beams will be constrained via 4 trailing links geometrically positioned to 'lock' the axle in place horizontally, the front beam lower will have actual convergence of the lower arms at the center of the beam, if my understanding is correct this places the roll center around 40mm above ground with the upper arms running as close as parallel as possible and sloping downwards in order to give a near horizontal roll axis to reduce roll steer. This has caused issues as it results in a short side VSAL which might lead to axle hop but I am not entirely sure as I don't fully understand the theory behind anti-dive/squat/etc.
The rear beam will be similar to the front however, there wont be a physical convergence point of the lower arms since the arms have to run around the sump, this also puts the roll center higher at the rear which if i understand correctly means that more load will be transferred geometrically resulting in faster response however, that is for independent suspensions so I am not sure if this is still true for beams.
The biggest problem is steering the front beam, in comparison to a double wish setup it is a real nightmare in my opinion, it's easy to draw up some ideas that 'might' work however, putting one into practice is significantly different and more difficult. My favored layout currently is one where a bevel gearbox is positioned at the top of the car with a 3:1-4:1 ratio attached to a column which runs down to the floor of the car and sits in a bearing housed in a cross member, the lower segment of the column is splined with a internally splined sliding pitman arm attached, this arm is then pushed up and down the column as the beam moves up and down thus preventing any wheel angle changes since the links remain the same length in relation to the beam. The issue with this method is that in order to get even 100% 'ackermann' gives a system where the uprights are steered from the front potentially resulting in an interference issue with the beam. Posted below are a few very rough drawings of various systems(some may not be accurate since they were only intended to show the method of steering the axle rather than the actual generated geometry):
http://i1296.photobucket.com/albums/...psewlhfvxw.jpg
http://i1296.photobucket.com/albums/...psu21dliug.jpg
http://i1296.photobucket.com/albums/...ps6y1vgo7x.jpg
(sorry about the general poor quality of the drawings and handwriting)
Finally, yes our beams look similar to those from prior art cars, yes I accept that it could be considered 'copying' by some but in our opinion it is fair game so long as we understand why we are doing what we are doing and our targets, plus, it's not like everyone accuses each other of copying their double-wish setups is it?
Onto a few extra things now. We have a set of cane creek DB coil shocks currently, in our opinion they don't fit in with our car concept since why does a car which is simple and for the main part non-adjustable need 4-way adjustable damping? It doesn't. We will do far better to run a fixed car and learn from it than we will by getting lost in adjustment. From a quick browse around it appears that the Kaz Tech quarter midget shocks will fit in with our car well, they are non-adjustable without a rebuild however, providing the dampers are spec'd within reason they should fall close to the 'optimum' required. They also lend themselves better to direct acting and potentially mono-shocks in the future since they have 70mm of travel.
I was also having a look around for some 8inch wheels and tyres to be used in the future. I came across these 'mini-cup' cars which for a start look like fantastic fun! (http://www.americanraceronline.com/tires/mini-cup/) and also have a slick pattern up to 8inch wide, I also found the chassis manufacturers site and a few photos to show how everything is packaged, if anyone is interested they can be found here: http://www.ncchassisco.com/chassis/mini-cup.aspx
Anyway, enough for now, see what you guys think!
Christian
Hey Christian, quick note on the American Racer tires ('Merica!). They are meant to be used in a spec series and used to help control wear and cost. Where as the Hoosier LC0 for minicup cars may last a night or two or less considering how much the amateur circle track guys dope their tires, the American Racer tires are meant to last a whole season with some left for testing. Here in the US, California-Berkeley and and Oakland University have both tried them with ill success. They are cheap on price, just right on size, but have been described to me as "driving on ice cubes". So far, I don't think anyone has discovered the magical "competitive 8 inch tire option" and typically anything this small is meant for small kids so it's not like they are marketing towards FSAE in anyway.
I think you might want to shun the idea of the hydraulic rack due to driver feedback requirements. Also, I'm not sure if it's legal.
Your chassis looks legal but you may want to check against a simulation as to how stiff that iteration actually is and if it meets your chassis weight/stiffness requirements. As a spaceframe team, one thing we did to great extent last year was use all of our body panels for chassis stiffening by making them load bearing. It helps narrow the gap between monocoque teams and space frames in stiffness, but you'll still be at a large deficit in weight compared to well done monocoques. I think ETS may have 40lbs less into their finished chassis than we do.
Have you considered ditching the third pedal? The clutch is only really utilized when getting the car going from a stop, so it may be more space efficient for you guys to move it to a handle somewhere. The ability to drive two footed with a bit more luxury/space between the pedals is also nice.
The Kaz quarter midgets may not not be adjustable without a rebuild kit (which means if you should get these shocks, get the rebuild/shim kit) but there is one thing that they have over the double adjustables: springs that fit with rates that are available in 5lb/in increments. The double adjustables as well as many others like Ohlins only have springs available in 25lb/in increments. It means you can get that much closer to dialing in your suspension to get exactly what you need. On the spot adjustability is the only thing you're missing out on.
On note of your rear structure I believe that your fuel tank needs to be protected in side view from anything that could get to it which I don't think this iteration currently does, but that just may be the angle unless there is space in front of the main hoop you're utilizing.
What differential do you plan on using?
MCoach - thanks for the detailed feedback :)
It's a shame the tyres are like concrete but maybe in the future it will be a viable option, as much as i loved the idea of making tyres like Delft i don't think it is ever a possiblity for our team so that kind of drops the 8inch wheels. Still, i think there's a lot of potential in the 8's if they can be made to work.
The hydrualic rack issues are something we're aware or and certainly legality is questionable, i have asked the Rules body to see if it is legal but i have yet to hear back, i understand the feedback loss is problamatic but i think it would be a good solution for a front beam if that could be considered manageable. One thing i was especially worried about with this setup was how to prevent the fluid boiling, i know that's a problem some of the UK drifters have and end up running power steering fluid coolers.
Bonded panels are on the list and we have a person who intends to do this but that's as much as i know currently.
See the third pedal is an interesting one, we currently have a centrifugal clutch in the car but it's never worked very well so that's why we made the decision to go back to a manual clutch this year. I'd prefer a hand clutch but i'm not the one making the decision on that but i will put it forward.
That's good news on the shocks, i know about the rebuild kit but quite honestly i'd rather not get one for this year or until someone comes along who i think is an appropriate person to rebuild them, basically, i don't trust any of the current members enough to rebuild them without screwing it up, not even myself at this point. So the less 'oh we could change this' the better i think.
Fuel tank will be of a triangular shape and pretty much the drivers backrest, we intend to have the driver sitting on the firewall which is inturn just infront of the tank, we will need some shielding to prevent the tank being heated by the manifold but we believe we can implement this without problems.
The diff we plan on using is the drexler but i think if i had unlimited choice i'd use a spool and have a good look at the geometry on go karts to see how they unload the inside wheel in turns. Why a spool? In my opinion i think you can build a very simple car that performs reliably, is easy to build and is fast without adjustment. As far as i'm concerned in our current state adjustment will only lead us down a blind alley so i'm trying to remove it where possible.
That's probably made a lot of people groan and question how you can have a car without adjustment but honestly i think we will learn more and be faster by just driving around any car problems we have and then working on those problems next year or if they're exceptionally bad we can always make a new part.
Depending on how much of the cars goals and requirements are based on previous cars, the design might be down a blind alley and you might not know it yet. I'm not saying you're wrong, just leave some wiggle room.
This year was our first car on 10s and it really is difficult to package things compared to a 13" wheel package. From talking to older members it had be done before, but poorly. From the time I joined the team we had always wanted to do it but there were so many opponents to it for various reasons...
But finally, we went ahead and did it anyway, however, we didn't really know where to start or where we wanted to end up. our 13" design could have just been scaled down but would that give us what we wanted? Maybe, maybe not. So we designed around what we thought it should be and gave it a lot of adjustment. Roll centers were 4 point adjustable front and rear, caster was adjustable by 6 degrees (ancient American secret), toe pick up points were adjustable through shims, a few more things than your typical FSAE car.
We didn't fully explore the adjustments before our stint at competitions this year, but it allowed us to take a look at where we may have been off, regroup, develop, and continue to understand how to better ourselves by educating ourselves of the consequences of moving it from it's adjustment and tweaking the adjustments as we develop new systems. We've only gotten faster since. So, some groans from me. It's nice to have the adjustment even if you may not readily use it. "Measure twice, cut once".
The way go karts unload their inside tires is a lot of caster. For an Aussie reference check out the Monash car from about the 2007-2009 era. I believe they ran a spool about that time. You could also ask them a bit about it's pros and cons and why they moved away from it. I think the Drexler is a solid choice based on the but have no personal experience with it.
As far as 8" tires go, mini-cups are no good from either Hoosier or American Racer. They are both way too hard. Hoosier will not do a custom run of them in the LC0 compound, either (Believe me, I tried! I even offered to buy a full run myself.)
I personally think a Hoosier 42400 could be competitive. It isn't as soft as an LC0, but is a heck of a lot softer than the mini-cups. It is treaded, but how much does that really actually matter? The tires are cheap, so maybe some of the 8" wheel teams could try them out.
http://www.racetires.com/shop/42400-...o-sprint-dirt/
Christian,Quote:
Originally Posted by ChristianChalliner
Very well said, IMO.
For those students who disagree with above quote, be reminded that Christian's School is a perennial tail-ender at FSUK. Sometimes when you find yourselves at the bottom of a very deep hole, you have to abandon all ideas of fancy fully-adjustable, titanium-runged, carbon-fibre ladders, and just start climbing.
Big-picture work seems to be on schedule, and now that it is December you can start fleshing out the details.
(Although ... could you please add Percy to your CAD sketches (ie. the 3 x hip/shoulder/head circles + ~0.9 m long legs). Percy is the most major part of all the big-picture bits, so he should appear in all such sketches.)
~o0o~
More Detailed Comments.
===================
BEAMS - Have you seen my recent posts on Beam-Axle Kinematic Design?
Your current ideas seem similar to B-A(4), namely a "W" shaped linkage in plan-view (with beam at top of W, and car-nose pointing down). This is similar to ECU's and UQ's rear-beam (edit: oops, not UQ), and is a good enough choice considering all the other FS bits that have to go with it.
Your front-beam also seems similar to this, but in side-view the links should be close to horizontal, to make the longitudinal n-lines through the wheelprints more horizontal (ie. ~0% anti-dive). (I still think the Model-T-Ford front-beam (ie. in Twin Beam-Wing sketch) is simply simpler, but it is a close thing.)
STEERING - Your BGB sketch is similar (I think?) to the arrangement on my B-A(5) sketch. I am quite sure that, if well-detailed, it will work fine. The R&P you drew will also work fine, except that most FS/FSAE R&Ps I have seen are poorly detailed! I would avoid the hydraulic-steering, except MAYBE as a 2-year project, perhaps started now, but not used til 2016.
Best is to stick to the earlier discussed aim of getting the whole car built early. Then, should some little details in the steering turn out to be less than ideal, there is still time for a bit of final polishing/improving before the comp. Worst case, in such an event you can always ask for suggestions here. :)
FRAME - "T3.12.5 The Front Hoop must be no more than 250 mms (9.8 inches) forward of the steering wheel..." <- This just a reminder.
Along with putting Percy in your CAD sketches, it is a good idea to give him some arms, and hands, and a steering-wheel.
Otherwise frame is OK. It will have lowish torsional stiffness, but with beams you can run springs that are so soft (or you can adjust handling via RC heights) that a wet-noodle frame will do.
For an easy approach to a simple+stiff frame, I suggest the minimum number of mandatory tubes (as you have done), then spot-weld a sheet of 0.5 - 1.0 mm thick steel (I suggest galvanised) to the bottom-rails. Use MIG with "spot welding timer" to fill ~3 mm diameter holes that are pre-drilled in the sheet every 20 - 100 mm. This means you do NOT need any tubular diagonal bracing of the floor, because the sheet does the bracing. And it also acts as ... a strong floor!
Add similar sheets (maybe even 0.3 mm thk) to the lower sides of the frame, make sure the MRH is well connected to the engine (because this acts as a "torque-box"), and the stiffness shoots up.
SPRING-DAMPERS - Again, the beams make this choice much easier. As before, with beams you can use very soft springs (ie. because no camber-change with Heave/Pitch/Roll), and with soft springs you only need low damping. The main decision here, IMO, is cost and availability. I would look for "low" and "easy". (Honestly, I reckon I could do it with some heavy-duty elastic bands! :))
TYRES - For future option of 8" wheels and tyres I would be looking to quad-bike off-road racing tyres. These are usually heavily treaded, but soft compound. So when half-worn they might work well. However, this would require the Team to do all the testing because (IIRC) the TTC cannot test 8" tyres (ie. too small...).
This is another good "2 year" project, where the student takes last year's car, retro-fits 8" wheels, etc., buys a trailer load of quad-bike tyres, then does endless figure-eights while logging lat-Gs, or just using stop-watch.
DIFF - Given you already have the Drexler, I would stick with it for now. Once the car is built and running, and assuming you have time, you can vary the Drexler so that it acts as anything from open to spool. Test to see what works best, or even "acceptably". If spool = good-enough, then make a bolt-on spool replacement for the Drexler, and save a few thousand quid in the Cost report.
Go-karts make a spool work by using Castor+Offset ... PLUS a stiff car (ie. mandatory no-suspension!). This also makes the driver work hard (ie. he has to lift the inside-rear-wheel up)! Heavier car = more driver work = ughhh! For your general set-up, I would suggest it easier to get a spool to work by fitting stiffer springs at rear (or softer at front), or a higher rear RC (up to ~axle-height), or both. This makes the centrifugal force at car CG do the work, and life is much easier for the driver.
LAST BITS - Miscellaneous comments based on quick re-read of your posts.
* Aiming for ULTIMATE low weight is NOT important now. Your good big-picture thinking will get you a long way in that direction. Your four-cylinder "ballast" stops you setting any records here, so your bigger-picture goals of getting the car built early and being well-tested are much more valuable.
* "Short SVSAL ... axle-hop" is NOT a big problem. If so, then after you post more detailed drawings I can tell you how to fix it.
* IMO, two-pedal car + hand-clutch = much better. Long term goal of "auto-box" (= NO clutch!) = even better! :)
Z
Erik, another quick note. Adjustments on systems don't need to be carbotanium or complicated. In fact, we didn't use either material for last years car.
for things like control arms or shims it can just be a matter of an extra hole or two drilled for the sake of knowing the difference in parameters and comparing calculations to real life. For shims it could also just be a matter of stacking washers in a different arrangement or more of them. I know that adjustable usually means more complicated, but there are simple ways to do some of these thing.
You caught me on the offset. Lots of castor + lots of negative offset could yield the opposite of desired results! :P
Lots of castor + some offset is enough to put your your desired tire in the air.
Agreed, the logis is the same with composite stressed panels but way simpler/cheaper. The Locost/Super 7 gang knows it for ages, with bonded & riveted aluminum panels dramatically increasing their torsional stiffness...Quote:
Originally Posted by Z