Just read your write-up again, Mark. For your drivetrain, you may need to consider an over/under chain loop for your drive motors, like we use in OCCRA. Since most drill motors are wound to output slightly less power in reverse, you need to run them both in forward and use the mechanics of the chain drive to invert the output of one side... If you don't the robot will most likely travel in a large arc rather than a straight line. Contact me if you need more details, it's difficult to put into words.