I am a Robotics enthusiast and planning to make a small and simple four wheel car whose motors are supposed to be controlled by an Android device housed inside the car by means of the micro USB port of the device. The car has to move forward or backward only as directed by the signals from the Android device.

So my assumption is that there should be a circuit board which accepts the signals from the microUSB/USB of the Android device and controls the power to the electric DC motor. Also the power for the motor will be supplied from a battery pack inside the car.

Could anyone suggest me a cheap motor driver circuit which supports micro USB or USB? And where can I get the parts for this online? I did a lot research but very confused with the technical terms which I am not familiar with.