CIM speed in reverse?

[colt527]

My team just finished building and mounting our first attempt at combining the Boshe Drill motors and the CIM aka Chiaphua aka Atwood motors. We matched the free load speeds of both using gears and some chains, and it tested fine while we had the robot propped up on a table, but when we placed it on the floor, one side was completely overpowering the other side and it was impossible to maneuver the robot.

The way our gearbox is set up is that both the Bosh Drill motors turn forward when the robot went forward, but due to lack of space and eagerness to see the robot move under CIM and drill power we had 1 CIM go forward and 1 CIM go back wards, hoping that the RPM difference was not too great in forward or reverse. Can this be the problem that we are facing? That the forward CIM is going so much faster then the back wards one that it is dominating the other side?

Thanks!