Just out of curiousity, were the maximum dimensions of your robot for before competion begins, or after deployment and full operation? Can arms and stuff unfold or expand past the initial limits in size? If you keep balls from coming over the wall in the first place, would that cut your work in half? And to win, you would only need to get one of your own balls over the wall?
I don't remember if you gave any specifics on the arena except the height of the wall.