I built a robot using 21 battery powered screwdriver motors. What is the best system for controlling this many motors? If I use an R C trransmitter,how many chanels will i need?
If all the motors need to be independent, then you will need 21 channels. In order to control them you will need DC motor controllers. You can find here all available RC DC motor controllers. Take a look at the GoRobotics article about Choosing the Right Motor Controller to help you choose the right one. The example at the bottom explains how to choose a motor controller for a DC gear motor.