non-CV cars

[Travis Garrison]

http://dot.etec.wwu.edu/fsae/HostedPics/2007_FSAE_West/Misc_Before_Gallery/IMG_1366.jpg
http://dot.etec.wwu.edu/fsae/HostedPics/2007_FSAE_West/Wednesday/images/IMG_1364.jpg

Not sure who the above belonged to, and I also noticed BYU had a similiar flex disk setup made from what looked like spring steel (can't find an image to post). Both look very nice, but I'm curious, how much plunge did the teams running these two solutions get?

Thanks...

[drivetrainUW-Platt]

Pretty sure they are off a BMW driveshaft assembly. They run about $80 a doughnut. I am sure they would work just fine.

[Travis Garrison]

But how much plunge can they handle? .125" per?

[MikeDutsa]

I did a tranny swap on my 1974 BMW 2002. I replaced the four speed with a five speed, only when I installed it the first time I did not shim it correctly, went threw about 3 exploded flex discs before correcting the problem.... makes me wonder just how long those will last with changing misalignment.

[Dan G]

BYU shots:

http://evilengineering.com/gallery/d/17257-1/IMG_4720.jpg

http://evilengineering.com/gallery/d/17251-1/IMG_4718.jpg

Slick.

[N.Tsuji]

I have noticed how I can get that rubber flex disc, but I cannot get any information about that carbon(?) flex disc.
How can I get it?

[Peter]

This (http://www.spinning-composites.com/) is what we (Delft) used the last 4 years. This year the team changed to regular CV joints due to the constraint you put on the suspension design and operation; the flex plate adds stiffness and has a limited flex range.

Here (http://www.dutracing.nl/images/stories/easygallery/52/1166663587_PICT4455.jpg)
is a picture of the 06 car with flex plates.

Peter
Delft 04UK 06FSG

[drivetrainUW-Platt]

Do you know prices? Those carbon ones look to cost as much as the cv joints would.

[Peter]

No sorry, I don't remember (has been a while, and I did suspension) but I don't think they were cheap.

I personally like the BYU system, as you would be able to test different thicknesses/stiffnesses. But from what I have seen and heard of the 07 car is that the regular CV joints system is not that much heavier, when you take all bolts, extra component mass, etc in to account. On our light car the added stiffness and limits on suspension design really hurt performance.

Peter
Delft 04UK 06FSG

[Travis Garrison]

Thanks for the BYU shots. I love that system, seems like a cheap and easy way to elimnate one of the heavier and more complex parts we had to make. I'm just curious if they had to limit suspension travel to make it work.

No comments from BYU? Either way, great work guys, the steel plates look killer.

[mtg]

Well, the BYU suspension was mega stiff, so that is a possibility. I'm also curious as to what the allowable plunge is on a typical flex plate CV setup.

[Haupt]

Originally the BYU suspension was designed around using the composite flex plates. This restricted the travel, but was overcome by the distance between the disks. The composite disks which we purchased, but abandoned for several reasons (extremely stiff which added to the roll resistance, and an extremely slow shipping time- 6 months) were designed to flex a max of 4 degrees each. By moving to spring steel the addition rolling resistance was eliminated, but there still is a limit to the amount of deflection they can withstand.

[Welfares]

We also run the composite flex disks.

We bought all ours when they were still made by GKN. At that time, they were 70 pounds each, i don't imagine they've gotten any cheaper.

There's decent weight saving to be made in the driveshaft itself, but it means you have to position your diff right on the axle line, and it also limits your suspension. They're pretty stiff.

[LU-Bolton]

Being the composite masters that we think we are, we also attempted a flexplate/carbon shaft drivetrain setup for 2007, but then scrapped the plan so it didn't end up on the car.

Our idea was this... steal GkN's idea and make our own fiberglass flexplates. This way we could design for the torque of our motor and the thickness and overall size of the plates so as to reduce the stiffness of the plate during suspension travel.

Physical testing showed that our glass plates passed our design/load criteria. However, we knew that the overall stiffness of the rear suspension was going to increase.... unfortunately we couldn't approximate how much. It's kind of a complicated system. Plus, as suspension guy, I wasn't quite sure how much of an effect it would have on the balance of our car from an initial tuning standpoint.

In the end, we decided that it wasn't worth our effort for a few reasons:
1. Added rear suspension stiffness already talked about
2. Fatigue? Our plan was to throw a flexplate mounted to a misaligned shaft on one of our lathes and let it run all week. We never got around to it.
3. Reliability, we couldn't afford to lose time due to a driveshaft failure in 2007. At some other time, it could have worked for us to do all the necessary testing.

Also remember this when designing for a flexplate system: Both of your shafts have to be equal length otherwise you will have asymmetric suspension stiffness characteristics. You should design your system so that the flexplates are not flexed at ride height, which if you look at most cars is not true. This is an annoying packaging constraint.

However, I do admit, the spring steel type plate is interesting and simple to implement as long as it has been tested.

Aaron Cassebeer

[Jimnik]

Yup, we're using flexible discs this year bought from Spinning-Composites. At 95 pounds each, they're not cheap to purchase and frankly we're not confident of their reliability.

But then there's the possibility, in the future, of making them in-house. Compared to the CV joints they should be much easier to design and manufacture. This is a big money saving opportunity.

It's a very complicated design but with some study and a bit of testing it should be possible to make them perform just as well as CV joints.

[Kevin Hall]

That is the University of Saskatchewan car. The discs are now starting to break up. If you are going to run such a thing, make sure that you have some spares around. They are indeed BMW parts...

[A_ndy]

The GKN flex discs were run on the very first Lancaster car back in 2000 (or was it 99) Anyway, they were the first team to run with them and used them in pairs at each end of an aluminium tubular drive shaft with Al tripod connecting plates. If I can find some pics I'll post them ...

[drivetrainUW-Platt]

Besides less weight on the carbon disks, I see NO good reasons to run anything discussed in this forum. They arent any cheaper then CV joints, they are less reliable and there are no packaging advantages.

Anyone have a better sales pitch to change my mind?

[Jersey Tom]

Agree with Mike on this one. Tripods aren't that expensive, and the housings are pretty cheap to fab in house.

[Travis Garrison]

I don't see why the composite or spring steel flex disks are less reliable when done correctly, and packaging isn't really the issue. The advantage as I see it is weight, CV joints are heavy and pretty much force you into the gun drilled axle path. A flex disk and tubular axle should be lighter, simpler and faster to build (I hate machining splines).

On cost, it doesn't get much cheaper than a water jetted plate bolted to a tube steel axle. Certainly cheaper than a gun drilled splined shaft mated to a tripod joint that fits into a relatively tight tolerance heat treated tripod joint.

So there's the sales pitch. Weight, build time and cost; three out of the four "holy grails" for FSAE. I know reliability isn't a given, but spring steel seems like a pretty damn simple and easy to analyze approach, hence the interest.

[Welfares]

We've been running the GKN discs since 2001.

Every one thats broken has done so because a control arm came off or something similar.

We also had something bend in our drivline that caused them to be running massively out of allignment, they delaminated, but didn't fail and still work.