It's a toughbox mini, the max speed is just under 9 fps I think.
Hopefully these two pictures shows how the axles are supported a little better. There is a piece of c-channel nested in the main one and slotted on the top and bottom so we can slide it to move the chain. The axle is supported in two places.
We used c-channel instead of 2x1 box because it seemed to us easier to bolt things on to c-channel than box. With a box frame, you wouldn't be able to get a nut on a bolt. Do other teams usually use rivets to avoid this problem?
I put chains on the outside on the middle to the back wheels, and the chains on the inside on the middle and front wheels. Maybe I'm wrong, but at the time I did it, it seemed like that would take less space and the wheel wouldn't have to be cantilevered as far. In any case, I believe the bumpers should adequately protect the chain, won't they?
*also, sorry for huge pictures, I uploaded them to Tinypic and didn't know how to make them smaller here.