Filter Capacitors . Large capacitors on the motor lines can help with both the noise from current drain variations, and with the reverse-voltage spike. Electrical Isolation . Mechanical and silicon relays both provide isolation between the control lines and the motor power lines. An exception to this is the Maxi-HBridge controller by Mondotronics , which provides optical isolation at the front of the circuit.
Isolation also means seperate grounds for motor and control voltages.
Ground loops can develop in the system. If RC servos are being used, this is not an option. Reduce Antenna Size . For the first rendition of my robot, I had a common ground plane, connected to the aluminum chassis plate that formed the base. When first separating the grounds between the control and motor systems, I left the chassis ground connected to the motor ground.