Actualy it is usualy just a mechanical system with a valve controled by the tiller and the rudder pedals through cables and a feedback, which closes the valve again once the desired angle is reached.
The control input from the rudder pedals is smaller.
On the 737, once the nose gear becomes airborne, the squat switch will give a signal to a small electrical actuator, which will disengage the rudder pedal input from the nose wheel steering mechanism, so that the fully extended gear can center itself through a centering cam inside the shock strut.
On the MD
-11 this disconnection is done purely mechanically.