Servo
From Combat Robot
An R/C servo combines an electric motor, an ESC, a feedback potentiometer, and a multi-stage gear reduction train into a compact package to respond to a control signal from the R/C receiver and provide position proportional motion in response to equivalent motion at the transmitter input.
Many servos may be modified to provide continuous forward and reverse rotation with proportional speed control. Servos modified in this way were once a popular drivetrain option for antweight robots. The availability of small ESCs and more powerful drive options virtually eliminated servo drives from combat robotics. Well illustrated instructions for continuous rotation servo modification may be found at Kronos Robotics.
See Also
Wikipedia article on Servo control
