Datasheet

A "Closed Loop" system can use the feedback signal to adjust the speed and direction of the

motor to achieve the desired result. In the case of an RC servo motor, the feedback is in the

form of a potentiometer (pot) connected to the output shaft of the motor. The output of the

pot is proportional to the position of the servo shaft.

The problem with controlling a standard RC servo motor from a microcontroller is that it is

'closed loop' inside the servo motor case, but 'open loop' with respect to your microcontroller.

You can tell the servo control circuit how you want the shaft positioned, but you have no way to

confirm if or when this actually happens.