[Mike Gray]

The Chiaphua motors are symmetric. The drill motors are, without question, asymmetric.

In a slow machine, the asymmetry probably makes little difference while the machine is in motion.
However, a fast machine will be difficult to control unless the drill motors are positioned as to keep them rotating in the same direction.

Whether the robot has a fast or slow ground speed, motor asymmetry will cause it to yaw during the launch. Over correction and speed reduction are common operator responses. Both result in decreased performance and sometimes genuine fear of using the full motor authority. Improper joystick trim can make the situation worse.

Spinning the drill motors in the same direction makes the driver confident that the machine will respond to his/her commands. High operator confidence generally results in good performance, but perhaps more important: consistant, repeatable performance.

The difference between forward and reverse speeds is about 12 percent as measured with a strobotach.

To illustrate the value of spinning the motors the same direction, make yourself a little "Segway" (TM) thingy with the CG below the axle centerline.
Power it with drill motors fastened directly to the wheels. It will refuse to run in a straight line. Its a good autumn experiment, or maybe between competitions.

Mike Gray