[MrForbes]

I would start by caculating the exact center of mass of the robot, then figuring out how far that is located from the edge of the robot where it will be resting as the righting action begins. Do a sum of the moments about one point, then you can figure out the force required to push the robot back upright. This will change as the robot moves, of course...so you probably need to evaluate it in several positions (or figure out a nice mathematical model of the whole operation, which sounds like too much work to me)