The Studica Robotics Multi-Mode Smart Servo features all-steel gears and large amounts of torque. 

The Multi-Mode Smart Servo 200 rotates at 200RPM. This angular programmable Servo can fill a variety of roles on your robot or project. In standard mode, it operates on a +/- 150-degree range. Using the Studica Smart Robot Servo Programmer (sold separately) the Multi-mode Smart Servo can be configured to run in continuous, standard, and custom angular mode. In continuous rotation mode, the servo will have proportional speed control based on the PWM signal that you send with your servo controller.