We decided to use 4 10" pneumatic balloon wheels, thus we needed a custom made frame (out of c-channel), custom belts (not too hard to find) and figure out a way to mount the hubs on them (this took us a whole Saturday because we had it right, then decided it was wrong and redid it, then found that that was wrong and reverted back to the original mount, which has worked perfectly), etc. The wheels helped us literally bounce over the defenses (we did have them slightly overinflated, the max psi they're supposed to have is 2.5 psi, but it's more fun with it bouncing
). I have only found one other team that used them, and they used 6 of them.