[team222badbrad]

If you wanted to get real crazy you could mount a setup similar to what starter motors use to the shaft of the big CIM.

If you design a pinion similar to what starter motors do as soon as they turn on to work in both forward and reverse you wouldn't have to worry about locking it or unlocking the motor from the wheels.

If your unfamiliar with starter motors what happens when you turn the motor is rather simple. The rotation or lack of rotation of the motor forces the pinion back and forth along the shaft to either engage or disengage a gear the pinion meshes with, usually the attached right to an engines flywheel.