I have an old 9.6V Dewalt drill with dead batteries.  This will make a perfect drive motor as the clutch will prevent the platform from turning when turned off and the motor has variable speed.  The only challenge will be to figure out the drive train.

But first I need to convert the drill to run off power.  I could just buy another battery but that in itself would cost over $40 and my goal is to spend as little as possible.  Also I believe I can control the speed via PWM by using a MOSFET driver and a DC Adapter.

With the battery pack disassembled, I’ve installed a 5.5mm jack to match the 9.5 volt adapter.