The Dynamixel AX-18A Smart Serial Servo from Robotis is a step up from the AX-12A servo providing twice the speed and 15% more torque. The AX-18A has additional feedback information such as speed, temperature, position and load. The Robotis AX servo product line features a simple, and robust, TTL level communication protocol. Over a single TTL signal line you can daisy chain several servos and position of several servos independently and read back their positions.