Aluminum Tripod Race

[dmacke]

Hello everyone, I am currently designing some aluminum races for our team's tripods but after running through the calculations, my calculations claim that they would not last very long at all, if at all. I know there are teams that run aluminum races without inserts or anodizing. Are these teams suffering the problems that I come to in my calculations or is there likely something that I am missing in my calculations? Thanks for your help.

[mech5496]

Not a drivetrain guy here, but I have to report that our team uses 7075Al housings (no liners) for three years in a row without a single problem.

[dmacke]

Ok great. I figured it was something with my calculations but I just wanted to make sure that I wasn't heading down I dead end before I spent any more time on it. Thanks for your help.

[kcapitano]

Hi dmacke

There are some other threads on these forums that discuss this very subject in some detail. Here are a few links:

http://fsae.com/eve/forums/a/t...20354151#19820354151 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/19820354151?r=19820354151#19820354151)
http://fsae.com/eve/forums/a/t...=229108404#229108404 (http://fsae.com/eve/forums/a/tpc/f/125607348/m/229108404?r=229108404#229108404)

What kind of calculations did you do? I did some using the Hertzian Contact stress equations and modeled the contact as a cylinder pressing on a flat surface (so a line of contact). My calculations also showed that the aluminum housing would yield, so I'm designing an aluminum hub with a steel liner for the tripod.

According to some teams you can get away with running tripods on the bare aluminum. I think the trick is designing the housing with the yielding of the aluminum in mind. I think if you play with the profile of the tripod race it can be done successfully.

[dmacke]

I also did Hertzian Contact stress equations and got the same results as you did. When you say that some teams design with yielding in mind are they making the tolerances tighter so that once it yields they will be near where they are supposed to be? How are you machining the steel liner if you don't mind me asking? I have heard of teams using a EDM but wasn't sure if you could do that same thing on a CNC for example.

[Kirk Feldkamp]

Or you could just buy them (http://www.taylor-race.com/part.cfm?id=6366&category=Chain%20Drive%20%20%2F%20FSAE&subcategory1=Aluminum%20FSAE%20Tri-pod%20Housing&popup=1) and move on to other stuff. Heck, they're not even all that expensive. If your calculations suggest that the contact stresses in aluminum have any possibility of causing a failure, wouldn't it make sense to reduce risk by using a material that's better suited to the task?

-Kirk

[kcapitano]

If I recall correctly, I remember one team posting that they cut separate profiles for each side of the individual tripod bearings. The profiles had a slightly larger ID than the OD of the tripod bearings, but were overlapped so the bearing still fit snug. Hopefully that description makes sense. If not I could try to post a sketch.

For the steel liner, it's less of a traditional liner and more like an insert-able tripod housing. I'll be cutting the full profile of the tripod housing out of steel on a CNC and then fixing the housing into an aluminum hub with pins around the OD. The pins will be stuck between the ID of the aluminum hub and the OD of the steel housing, half in each (basically forming a spline connection).

If you were considering using a typical steel liner, then I would just purchase liners and design around them.

[Ben K]

Originally posted by Kirk Feldkamp:
Or you could just buy them (http://www.taylor-race.com/part.cfm?id=6366&category=Chain%20Drive%20%20%2F%20FSAE&subcategory1=Aluminum%20FSAE%20Tri-pod%20Housing&popup=1) and move on to other stuff. Heck, they're not even all that expensive. If your calculations suggest that the contact stresses in aluminum have any possibility of causing a failure, wouldn't it make sense to reduce risk by using a material that's better suited to the task?

-Kirk

180 bucks vs a huge amount of time doing design and machining work. There is no way you can make these for cheaper than just buying them. (And they'll probably work out better)

+1

Ben

[swong46]

Originally posted by Kirk Feldkamp:
Or you could just buy them (http://www.taylor-race.com/part.cfm?id=6366&category=Chain%20Drive%20%20%2F%20FSAE&subcategory1=Aluminum%20FSAE%20Tri-pod%20Housing&popup=1) and move on to other stuff. Heck, they're not even all that expensive. If your calculations suggest that the contact stresses in aluminum have any possibility of causing a failure, wouldn't it make sense to reduce risk by using a material that's better suited to the task?

-Kirk

They make these in a Formula Student size? Last time I talked to Scott, they didn't have small enough versions.

[Dash]

Originally posted by swong46:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Kirk Feldkamp:
Or you could just buy them (http://www.taylor-race.com/part.cfm?id=6366&category=Chain%20Drive%20%20%2F%20FSAE&subcategory1=Aluminum%20FSAE%20Tri-pod%20Housing&popup=1) and move on to other stuff. Heck, they're not even all that expensive. If your calculations suggest that the contact stresses in aluminum have any possibility of causing a failure, wouldn't it make sense to reduce risk by using a material that's better suited to the task?

-Kirk

They make these in a Formula Student size? Last time I talked to Scott, they didn't have small enough versions. </div></BLOCKQUOTE>

Yes they do. The particular ones linked are for the FSAE sized tripods they sell. While the OD is a tad large, its quite do-able.

[KustomizingKid]

We have run aluminum tripods on both ends of our drive shafts for the past decade with no problems.

[MCoach]

Originally posted by KustomizingKid:
We have run aluminum tripods on both ends of our drive shafts for the past decade with no problems.

As have we.
Do you run yours with any sort of surface protection (coating, anodize, etc.)? Just curious.

[scotty young Taylor Race]

Working on Inserts only right now...
They will be around 30mm wide. and made for our 02002011 tripods.

[coleasterling]

Does this mean that yall had problems with the aluminum housings/stub shafts on the prototype and are moving away from it?

[scotty young Taylor Race]

Cole.

For the time being yes..... But we have not scraped it ....