The ros_control packages takes as input the joint state data from your robot's
actuator's encoders and an input set point. It uses a generic control loop
feedback mechanism, typically a PID controller, to control the output,
typically effort, sent to your actuators. ros_control gets more complicated for
physical mechanisms that do not have one-to-one mappings of joint positions,
efforts, etc but these scenarios are accounted for using transmissions.

Homepage:
http://wiki.ros.org/ros_control
