Hex Shaft Wear Experiences

[mwibbels]

We did a post mortem on our AM Toughboxes today after 2 regionals and the championships. We were surprised by the wear on the gear that mates with output hex shaft. The hex shaft worked the gear over pretty well - the robustness of the system was reduced by the gear material selection and the generous pilot hole drilled for the broaching operation, but still it was a surprise.

The gear did not fail, but it is a cautionary example for us. We have been thinking about using hex drives for our wheels, in a west coast configuration, and are reconsidering the material and geometry choices for the wheels given our experience with the AM transmission's hex drive - a system with minimal lateral stress as compared to the wheels.

We would be very interested to hear from teams who have used hex broached drive wheels in aluminum or softer materials - specifically if they have issues with the hex shaft deforming the wheel hole and if it is something that they design around. Wider hubs, steel keeper plates on the face of the wheel, clamping the wheel using the keeper screw in the end of the axle and a collar on the hex shaft, living with the wear, and swapping the wheels all seem to be possibilities, but perhaps there are simpler solutions - or it really isn't an issue within some design constraints?

Inputs?