unless you start spending silly amounts of money on a drill , jsut to hack for a bot. The speed controller sare eather switches (so on off) or are extremely underpowered and one way . You would actually need 2 servos as youd need one to push the trigger ad one to reverse the polarity using the switch thing. This would require a micro controller to control the 2 servos from one channel and after all of that , it wouldnt work very well either. esc's are getting so cheap , unless you really go some , its gona be cheaper to et a dedicated esc . nt to mention a lot better for your robot.