Wheel Layout/Attachment Design

[Andrew Blair]

This might be a trivial question, but what is a better wheel attachment design? Bolting the wheel onto a hub (think car wheel), or supporting the axle at both ends and letting the wheels spin free (or drive the axle itself)? I can think of good and bad aspects of both designs, but what have teams experienced? Our team has stuck exclusively with supporting both axle ends.

[sanddrag]

We had external wheels this year and didn't have problems bending the 1/2" axles when we took hits but we had problems with the actual wheels themselves bending. Looking back, the wheel design could have been stronger so that wouldn't happen, but we didn't forsee the problem at the time.

Especially with a width of only 28", external wheels can give you a wider track for greater stability. Internal wheels are more protected, but the setup may weigh more and/or take up more space. I think it is all a matter of preference and design constraints placed by other subsystems. I don't think you can positively rule in favor of internal or external wheels.

[Andrew Blair]

How were your axles supported so as to keep them (and the frame/support device) from bending?

[sanddrag]

Originally Posted by Andrew Blair

How were your axles supported so as to keep them (and the frame/support device) from bending?

You can sort of see in this pic. The frame side rails are 1.5x2x1/8 6063 aluminum box tubing. Pockets were cut in the sides of the frame rails for pillow blocks to go in (and slide). The pillow blocks had 1/8" that went into the pocket in the frame rail and 3/16" that rode outside on the surface of the frame rail. There is a pillow block on the outside side of the frame rail and on the inboard side. We used standard 1/2" id flanged ball bearings from Small Parts and 1/2 precision keyed shaft from McMaster. The wheels were custom machined from solid 6061-T6 blanks and the spokes are 1/4" thick. Surprisingly, the wheels bent and would run out of true since there was no real 3rd dimension to the design of the spoke other than its thickness.

So putting it simply, you have a frame rail. You have a live axle go through it. You have a bearing on either side of the frame rail. You have a wheel outboard and a sprocket inboard.

For the frame rails, we could have gotten away with only 1" wide instead of 1.5" like 22, 254, and 968 (and probably others) do.

Edit: Here's another good pic of the setup.

The outboard pillow blocks had through holes and the inboard pillow blocks had threaded holes and the screws went through the frame rail and they clamped together onto the frame rail.

Let me know if you have any further questions.