[lukevanoort]

This is exactly what happened to us at VCU last year. See, with your robot's drive geometry it can't turn. What's happening is the insane torque of the drivetrain is twisting the chassis so one wheel is no longer in contact with the ground. Since that wheel now has zero traction and no real effect on turning, it becomes a 3WD that can turn. Then, the chassis flexes back, since you don't have the force to keep it up anymore, starting the cycle all over again.

Now, as to fixing it, we packed our treads with epoxy clay last year, and it worked like a charm. After a while, though, it started to crack and fall off (epoxy clay is brittle when dry), so we reapplied at the championship. It also looked way better than a bunch of zip ties wrapped around the wheels.