[Kit Gerhart]

If you gear the chip motors to match the drill motors in low gear, there would be very high drag from the chip motors if you run the drill motors in high gear. If you want to shift gears with the drill motors only, you should gear the chip motors to match the drill motors in high gear. Then, when you run the drill motors in low gear, you can use separate PWM outputs to the chip motors and run them at maybe 40% the power setting of the drill motors. You can experiment with this. You would want the chip motors to be pulling a little, but not anywhere near 'full throttle' when the drill motors are full throttle in low gear.

I don't know what kind of gearing you plan on running, but if you gear for not over 10-12 feet/sec in HIGH gear, you should have wheel spinning/tread sliding power from the drill motors in LOW gear without much help from the chip motors. I know that from our experience. Having the chip motors there will give you you much better high speed performance when the drill motor gearboxes are in high gear. You should be able to gear even higher than the 10-12 ft/sec I mentioned if you're running the four motors, but you will be getting into shakier territory in regard to overheating motors and possibly tripping breakers.

I hope this all makes sense. If you have any questions, let me know.