PMW and Servos.

Other Hardware Motors, Mechanics, Power and CNC
1

So this is what I understand so far about controlling servos with PMW

The angle of a servo is determined by the duration of a pulse that is applied to the control wire. The servo expects to see a pulse every 20ms. The length of the pulse will determine how far the motor turns. For example, a 1.5ms pulse will make the motor turn to a 90degrees position. When a servo is commanded to move to a position, it will not hold that position forever unless you command the position to be repeated.

My question is this:

So say the duty cycle is at 1.5ms with a period of 20ms and the servo has turned to 90degrees, what is stopping the servo turning beyond 90degrees? The servo is receiving 5v for 1.5ms, what makes the servo stop at 90degrees when there is power running through it continuously?

2

The signal doesn't power the servo, its a signal.
The servo control signal is read by the microcontroller inside the servo and used
as input to a control loop that operates the motor and observes the servo position using a
potentiometer or encoder.

3

A page that shows what is inside a typical hobby servo.

http://www.seattlerobotics.org/encoder/200009/S3003C.html