Servo Tester Diagram
 R1 = 18K
 R2 = 680K
 P1 = 50K Potentiometer (Linear)
 C1 = 0.033uF (33nF)
 C2 = 0.1uF   (100nF)
IC1 = LM555 Timer (or equiv.)
 D1 = 1N4148
The circuit above speaks for itself and does not need any more explanation, in my opinion.
The Servo control arm can sweep from 1 to 2mSec at approximately 7mA (4.8 volt assumed).
PPA is 4 volt at a frame rate of 16 mSec. This is a cheap and worthwhile project. Not only can you check the proper working of your servos you can also check for 'drag' or excessive rubbing when the servos are installed in your aircraft.
Copyright © 1995 Tony van Roon