Rubber mounted rear sprockets

[Gonzo]

Just considering if we need a rubber mounted rear sprocket to take the shock loading at starts and gear changes. Apparently bikes run rubber damping in the wheel hub.

We are considering running the rear sprocket on rubber bushes which are through bolted to the diff housing. The sprocket will also be radially located onto the diff housing.

Does anyone else do this? If not is that because of the extra complexity or is the shock loading really non-critical?

[Big Bird]

We had some rubber dampers actually on our stub axle mounts to put a bit of damping in the system, after we kept breaking sprocket drive bolts on our 02 car. It's worth noting that the 02 bolts were tiny, they would have broken whether they were damped or not.

Personally I wasn't happy with the 03 design as we had it, I thought the damping we had in there was too far past the sprocket to do much good. (After all, some nice big rubber dampers called tyres were only two CV joints further down the line). But sometimes for the sake of harmony you have to just let things go....

For what it is worth, we haven't broken any sprocket mount bolts since.

I like the sound of your design Mr Gonzo, go for it. Make sure the rubber you use is up to the task, i think we went through a few different types before we found one that worked. Couldn't tell you what it was though.

Cheers,

[Gonzo]

Couldn't tell me or won't tell me Mr Bird? http://fsae.com/groupee_common/emoticons/icon_biggrin.gif I thought the boys were being a bit over cautious with rubber mounting, but if we need it then we need it.

By the way congratulations on your win. Gary and I we pleased to hear of your success. Trust all is going well for 2004.

[Big Bird]

Can't tell you because I haven't got a bloody clue. In fact some would say that about most of my input over the past 18 months http://fsae.com/groupee_common/emoticons/icon_smile.gif

Hey, this might be the first thread ever to be fully subscribed by puppets. Kermit, you out there mate?? Miss Piggy?? We could even get a cameo appearance by Angry Joe as Oscar the Grouch....

Cheers,

[Kevin Hayward]

Gonzo,

I can remember looking at rubber mounts in our first year for the same reasons. In the end we did some rudimentary testing and decided not to run with them.

It has probably increased shock loading but the only consequence we may have had is increased wear of some parts ... nothing has catastrophically failed as a result.

Mind you our rear sprockets have been mounted mounted with 8 m8 bolts ... takes a lot to shear those unbrakos.

Personally I wouldn't worry about rubber mounts ... I don't think many teams use them either. However I would design component sizes for those shock loadings.

Hope this helps,

Kev

UWAM

[Chris Clarke]

We do not use rubber mounting of our sprocket and have been successful without them. It is something that I am looking into using though.

I know that the University of Victoria uses 5 stock bike rubber mounts to mount their sprocket on. I think they are off of a Ducati. It is a pretty nice set-up.

We use 12 grade 8 bolts to mount our sprocket. The only trouble we had in the past is when someone put grade 5 bolts in. We sheared 4 of the 12 bolts.

Speaking about shock loadings, we are currently looking at the sizing of our driveshafts. Since we brake through the differential, the driveshafts will be seeing braking force. Does anybody have an idea of what the braking shock loads are like? Or know a good book where I can read up on them? I am under the impresssion that they will be much higher than the driving forces.

[Daygo Nighthawk]

This being our first year at UCSD, we built ours without any (designed) dampening through the system. Then again, our car is built like a tank/volvo, so most things we wouldn't have to worry aobut.

I think the first to go would be half-shafts and differential carrier assemblies. Diff carrier was plenty strong this year, but also plenty heavy. The half-shafts were the weakest point in my opinion, and most susceptable to failure.

Quaife differential uses 10 x M10 bolt holes to secure the sprocket (or ring gear for gear drive)..
I used 5 x M10 bolts, left the others empty and never lost a minute of sleep over it.

From our test car, there's a picture of me somewhere holding a 4130 halfshaft that got twisted like crazy.. probably 90 degrees axially. Guess it scared me a bit.

[Denny Trimble]

My post wouldn't go through yesterday, so I'll try again.

We used to break stuff, then we went to a cush drive, it took a couple years to get it right, now we don't break stuff, but we also have CNC'd halfshafts with large radii going up from the minor diameter to the spline diameter, dowels transmitting torque to the diff instead of bolts, better heat treatment and surface finish, etc.

I think the cush drive helps, I don't know for sure if we need it anymore now that we're building things better.

The last drivetrain part that failed was a non-heat-treated stubshaft, and it was in the braking direction (center rear brake). Yes, the forces can be higher in braking than driving if you get "chatter".

[Charlie]

The chain chatter under braking problem is probably the worst loading. However in general I'd think acceleration would be worse because your tire really dictates maximum loading.

We don't run any kind of dampening setup except the big round black ones that the wheels hang in. Our shifting is pretty hard on it too, we see pretty significant wheel slip after a shift.

[Vector006]

I recall a post made a while ago from a team using a remote strain gauge on their halfshaft and recorded shock loads 5X greater under braking than acceleration...im assuming the spikes were from chatter.