Minor Problem, our robot DOESN'T work!

Problems:

When the robot is on top of boxes the wheels turn fine, but when we put it on the ground it starts to skip.

With a one stick control scheme:
When we push forward or backward, one wheel side starts truning before the other.

The motor has serious overheating porblems.

Thanks in advance.

It would be nice if you gave us the information of what motors you are using and a little bit more of a discription of what is going on. But from what it sounds like you are using the drill motors. If you are then the reason why they are turning at differnt rates is that you have them wired backwards. They are designed to travel fowards(cw i believe because that is the direction drills usually operate) faster than backwards(ccw). If you wire them so that both are wired the same then you really will not see the problem. Also if your motors are overheating then you probably do not have the motors geared correctly. Aslo of the robot is skipping while turning this means that your wheel base wide and this is what is causing the robot to be very hard to turn.