Do you know whats making it tip itself over instead of transferring the power to the other bot?
Its all about leverage. The pivot point of the arm, where the motor is, is about half way into the robot. The forks at the front are supposed to help lever onto the floor so more of the upward thrust goes into the lift of the opponent. However, the forks are 3mm thick and have a tendancy to bend.

If the pivot point was at the back of the robot as originally intended (there is a post from about November/December time showing where I originally wanted the motor to be, it would probably be better. Originally, the motor was far forwards but it meant the robor was forever turning itself over.