Double tripods

[Dunk Mckay]

We've been running inboard tripod joints and outboard fixed ball joints for the past few years and double sliding ball joints (VL) before then.

I'm looking to make the move to double tripods but have one or two questions about lateral restraint. With a pair of tripods and lateral force is going to throw the half shafts left and right and have them bumping into the housings and causing all sorts of trouble.

Solutions I have seen or thought up are as follow:

-put some rubber/nylon bumps stops in the ends of the shafts and accept that they might get thrown around a little bit but not too much damage will be done. -- I don't like this

-do the same as above to prevent damage in case of bottoming out, but make sure the boots are tightly fixed to the housings and half-shafts so that these are held roughly central between the two tripod housings, boots deflecting equally at both ends (give or take). -- I think this could be ok.

-have springs fitted between the ends of the half-shafts and the tripod housings (with shoulders for it to sit on) with a preload to hold the half-shafts in place. -- Should work nicely, but I don't like what would happen if one of the springs came off.

-have a spring as above, but only at one end of the shaft and positively fixed to the components, rather than held in place by a preload. This will compress and extend to allow for plunge travel, but will again stop excessive lateral motion due to shaft inertia. -- This seems nice and safe to me, but would, I think, make design and manufacture more complicated.


Personally I'm leaning towards option 2, but was wondering what other teams run or think would work. I had meant to ask around at comp this year, but had other things to talk about as well and was pushed for time.

[wagemd]

I would strongly recommend option four out of what you listed. I don't think the boots have nearly enough spring force to do the job. We run something like your fourth option, and tend to need fairly significant springs to keep things where we want them.

[Dunk Mckay]

Do you use the spring in one end to push the other end up against the tripod housing (essentially making it fixed)? Or is the spring used in tension and compression to hold them both central?

[kcapitano]

Have you looked at the kits that Taylor Race offers? They use a system similiar to what Dunk is talking about. A spring at one end pushes the shaft into the bottom of the opposite housing, thereby fixing the shaft in place. They also use rubber snubbers to make sure the tripods are never bottoming out.

FSAE Plunging System (http://www.taylor-race.com/pdf/plungingsystemweb1.pdf)

On the other hand, I spoke with Dan Lentsch from RCV performance, who also offer an FSAE tripod axle kit, and he said a plunging system was not necessary.

We are currently running inboard tripods (from RCV) and outboard CV joints. The shafts have no lateral retention so they are free to float. We have noticed some peculiar wear marks on some of the tripod bearings and we're keeping our eyes on them, but they haven't blown up yet and we have almost 500km on the car.

[Smeller]

Originally posted by Dunk Mckay:
Do you use the spring in one end to push the other end up against the tripod housing (essentially making it fixed)?

Thats how the solution from Taylor Race works, with the spring inside the hollow axle.
http://www.taylor-race.com/pdf/ACF4CC.pdf

[Paul Achard]

Not to advocate carelessness, but we've run double tripods for at least 4 years now, with no centering system, and have had no failures. We have noticed imprints left by the ends of the driveshaft splines on the insides of the tripod cups however. Putting nylon caps on the driveshafts should be a no-brainer imo, since it could also prevent the tripod bearings from hitting the ends of the races.
I don't think the springs are necessary; I could imagine they would be something of a hassle to install whenever you pull your drivetrain apart...

[Bemo]

We are also running the Taylor drive shafts with a spring at one side, which is holding the shaft in place. For us this solution always worked fine.
Assembly isn't an issue with that. I've done it a couple of times myself. If you're a bit careful it isn't a big thing to get it all in place within a couple of minutes without damaging anything.

[mech5496]

I will double Paul on that; no need for the extra hassle/complexity for springs there.

[Richard Pare]

From 30+ years with every conceivable system used from F1 to FF:

Stick with putting plastic "buttons" into the ends of the driveshafts. You will want the end to be rounded, and the CV flange needs to have either a flat face (not very good design-wise) or a spherical recess that has its center approximately at the center of the joint.

If the button will cross over any hole in the base of that recess, you can easily just plug the hole with an alu plug.

We've used this system for 20+ years, and have never had any sort of failure. It is simple, reliable, and cheap - a combination that is hard to beat.

[Scotty82]

A pre-load on a tri-pod axle is a must, A tri-pod is a non centering joint unlike a CV joint. If not kept in a pre-loaded state the axle will go through a series of harmonics and the axle assembly will dart back and forth within the housings. If there are no types of bump stops the tri-pod rollers will bottom out in the housing and will fail.

It is a simple and easy design. It is a design that has been incorporated in racecars that use tri-pod drive axles for years. Van Diemen , Swift , Ralt , Pro Mazda and many more…

If you feel you need to gamble a year’s worth of hard work for a simple proven system that you have been told you don’t need ... then I disagree… supplying parts for 300+ teams. I see tri-pod failures all the time because of this.

[Dunk Mckay]

Any advice on values for spring rates, spring sizes etc?

I'm guessing to do it properly it's gonna depend on the half-shaft mass, the shaft angles, suspension travel etc. But if standard systems are available rough values that work in most cases must be possible.

[scotty young Taylor Race]

Hey Dunk... Here is some info on the spring we use. These are fine up to 12 degrees axle angles.




Outside Diameter 0.360 in
Hole Diameter 0.375 in
Wire Diameter 0.059 in
Load At Solid Length 35.100 lb
Free Length 2.500 in
Rate 31.20 lb/in
Solid Length 1.417 in
Rod Diameter 0.231 in
Number of Coils 21.3
Total Coils 23.3
Finish ZINC PLATE AND BAKE PER ASTM B633
Material MW

[MCoach]

Originally posted by mech5496:
I will double Paul on that; no need for the extra hassle/complexity for springs there.


Why not a system where one side has a fixed spherical bushing at the tip which then has an internal (plastic/balsa wood/etc) shaft that is inside the axle which springs the other spherical bushing in the opposing tripod. I mean, it's not like you are using all the material inside the axle. It's only that OD and some wall thickness that really matters.

Moment of intertia, yo.


Edit: just noticed that Taylor does that already. Nice.