[Chris is me]

Originally Posted by llamadon

Hi, our team is prototyping a wcd this summer, and we have an excess of andymark Churro extrusion (http://www.andymark.com/product-p/am-2595.htm) and plan to use it as a live axle. Does anyone have experience using this material? If so, is it strong enough?

Originally Posted by Akash Rastogi

I wouldn't even use regular 6061 hex shaft for this application, let alone the 6063 churros. Bad experiences with bending and snapped axles. (Just ask 2791, among others).

Akash is right. Do not use churro tube as West Coast Drive cantilevered axles!!! I would go so far as to say that churro tube shouldn't ever be used as a live axle in any drivetrain.

There are a multitude of reasons churro tube is bad for a cantilevered axle, most of which have been touched on already. The profile shape is atrocious in torsion, which means your shaft will twist and possibly snap under heavy drivetrain loads. The material is 6063 aluminum, which generally has a lower yield strength than even 6061 aluminum. I suspect you would also have problems with bending or transverse shear loads, especially since the shaft has a giant clearance hole going all the way through it.

Originally Posted by asid61

6061 1/2" hex will not bend in drivetrain applications, as we had to substitute a few 7075 axles for 6061 during build and they held up through 2 competitions.

This is absolutely, positively not true. It's okay to post your experiences on CD, but don't use that information to make blanket statements about all drivetrains. At least not without solid evidence or reasoning.

This might have been due to to other drivetriain problems that stopped us from moving too much though.

This is exactly why you didn't have any failures. Failure is not always instantaneous.

To share a story, 2791 used 6061 hex stock to make drive axles in 2011, and we had numerous failures. Both center drive axles failed halfway into our first event. One center axle, if I recall correctly, actually stripped itself from hex to a rounded profile. Another split in half in an apparent torsion + shear failure. These were solid 6061 axles without intermediate snap ring grooves or other stress risers.

Originally Posted by asid61

I'm sorry, it did not bend for us. Our drivetrain didn't see very heavy use this year, and that might be why it worked fine. Teams like 254 probably would need the extra durability afforded by 7075, but for a prototype low-load drivetrain 6061 should be fine.

What's the point of building a prototype drive if you're not going to test durability? If you're building a drivetrain before the season starts, you should build as close to how you would in build season as you can. That way, if and when you do have failures, you can directly apply them to your future robot. If you use parts you know will fail to cut corners, you won't know if the part you intended to use in build will work properly.

Originally Posted by cbale2000

We used some Churro for our collector on this years bot with no issues...

You can't really see it in that picture because the PVC spacers cover it, but it extends across the entire length of the collector, drives the wheels, and is only supported on the ends. Overall we've been very happy with it, especially because it's light and rigid (and because we already had some around when VEXPro ran out of their long hex stock during build season).

Now granted this application probably undergoes far less force than something like a drive system would, so keep that in mind when planning its use.

We also used churro tube for our collector this year. This was partially because we were out of hex stock and partially because a collector is probably the least loaded part of our entire robot. The loads a collector shaft sees, unless exposed to a high speed collision, are extremely low.