2.0 ms with the pulse being 1.5 ms when the arm is in the center (just like the transmitter stick!).

The pulse generator within the servo only generates a pulse when an incoming pulse is received from the receiver. The receiver pulse "triggers" the servo's pulse generator. What we now have in the servo is two pulses, the pulse from the receiver and the servo's internally generated pulse. Both pulses start at the same time, but depending upon the position of the transmitter stick, versus the position of the servo arm, they may not end at the same time.

Lets first look at the operation when both the transmitter stick is centered, and the servo arm is centered! Under this condition the incoming pulse would trigger the servo pulse and both pulses would start at the same time, and end together 1.5 ms. later. When this occurs the servo does nothing.

Now let's move the transmitter stick in one direction, and as stated before we will alter the length of the pulse to the servo. For this example we will say that the pulse became longer. As before, the input pulse triggers the servo's internal pulse generator and the two pulses start together, but this time the input pulse is longer than the servo's internally generated pulse and they don't end together.

We will now introduce the second circuit in your servo called a "pulse length comparitor". This circuit gets input from the incoming signal and the internal pulse generator, and as its name implies, compares them. The output of the comparitor will be a signal which either indicates that both pulses are equal in length, the incoming pulse is longer, or the incoming pulse is shorter. How much longer or shorter the incoming pulse is versus the internally generated pulse does not matter.

Now enters the motor driver circuit. This is the circuit which applies power to the servo motor. The servo motor is a DC motor, which means, if we connect the power to its terminals one way it will turn in one direction, and if we reverse the polarity of the connection it will run in the opposite direction. The motor driver circuit does just that.

Depending upon the signal it receives from the pulse comparitor, it will either run the motor clockwise, or counter clockwise.

Let us assume that for this condition, where the input pulse is longer than the internal pulse, that the motor is run clockwise. This in turn rotates the output arm which is connected to the "feedback pot". As the output arm rotates, the length of the servo generated pulse increases. The servo will continue to rotate until the "pulse length comparitor" senses that they are both equal in length, at which time the motor driver circuitry will turn off the motor.

If we were to move the stick a little further in the same direction, the pulse comparitor would once again detect a longer input pulse and signal the motor driver circuitry to start the motor running clockwise again until the pulse lengths match.

If we were to return the stick to neutral, the input pulse would be shortened, the pulse comparitor would detect this shorter input pulse and signal the motor driver to run the motor counter-clockwise until the pulses matched.

What we now see is that our servos are "error correcting" and not "self centering" as we may have thought. By this I mean that the servo only moves when it receives an input pulse which does not match its internal generated pulse. If we were to loose the signal to the servo it will remain where ever it was last positioned.

In order for our servos to faithfully track the transmitter stick position, we must constantly provide it a stream of input pulses for it to compare and adjust to. When we get to transmitter and receiver operation we will address the "frame rate" (repetition of pulses) which is sent to the servo, but for now we will just say that the servo receives a input pulse about every 20 ms, or about 50 times a second.

For those wondering , the servo motor is not pulsed 50 time a second when it is moving. The output of the "pulse length comparitor" feeds a "pulse stretcher" which in turn feeds the "motor driver