[Jon Stratis]

Stappy-

There is no requirement that your wheels are contained, but there are other requirements that may apply to your situation.

First, the frame perimeter must consist of "fixed non-articulated structural elements" (R2). Basically, this means the outer most corners have to be some sort of structural frame, not a wheel, as a wheel is articulated. So you need some frame material that extends into the corner.

Second, the bumpers must protect at least 8" on each side of the FRAME perimeter (R19).

Third, bumpers must be supported by your robot frame/structure (R26), with specifics as to the allowable distance between the bumper plywood and the frame/structure of the robot. And a minimum of 1/2" must be supported on the end of each bumper segment (also R26).

When you put this all together, it means you can't have rectangular bumpers on an octagon - you couldn't properly support the corner of the bumpers and would likely have difficulty with the 8" rule as well. Plus, that could effectively increase the overall size of your robot beyond the allowed 120" frame perimeter. Now, if you have 8" wheels, you also may find it difficult to support the bumper with robot frame/structure every 8" down the side (or on the end of the bumper if you opt for an 8" "corner bymore" type design) without having robot frame that encloses your wheels.