Harbor freight drill motors are commonly used for combat robot projects due to the cheap price tag. 20$ for a motor and 18V Ni-Cd, hell yeah! The problem I had was finding a motor controller for under 100$ per motor. I managed to scrape together a 30A setup which costs about $15 per motor, plus an additional $10 for an arduino which can support up to 4 motors. The motor controller has a 0-5V analog input, then use the dual relay board to control the direction you want the motor to spin. I have included a wiring diagram and links to two board used. I originaly purchased these boards on ebay, so if you buy the ones linked it with be ~28$. Cordless drill - http://tinyurl.com/hc5fwsq This is the same cordless drill that harbor freight sells for 20$. Motor Controller - http://tinyurl.com/MotorContro... One note is this controller linked does not have master and slave mode. You would have to cut off the potentiometer and run the yellow wire to the arduino. Dual Relay Board - http://tinyurl.com/5vRelayBoar... These are like 4$ on ebay. Yes I know this is 30A and the controller is 40A, its fine... Short run tests didnt generate any heat, will update after more strenuous testing. I do not have any code to link atm. But here is a good "how to" post. http://rcarduino.blogspot.com/2012/04/how-to-read-multiple-rc-channels-draft.html