Finding written information about almost any subject on the Internet is usually not too hard to do, but finding a good video that demonstrates the concept can be a challenge. Such is - or was - the case for learning how the timing waveform for an R/C servo works. Here is a short video that shows how the pulse that control servo position varies in width between 1.0 and 2.0 milliseconds (ms) over the full travel range of the servo. That 1.0 millisecond width includes the full range of the transmitter stick and the trim tab. I have seen comments on forums from people who were only measuring around 1.2 to 1.8 ms, so my guess is that they were not including trim tab range.
The pulse repetition rate is approximately once every 20 milliseconds. The diagram shown below illustrates what you see in the video where the Channel 1 pulse varies between 1.0 and 2.0 ms over the full transmitter stick + trim range. You will also see in the video how each successive channel's pulse begins where the previous one ends. For example, Channel 2's pulse begins at the end of Channel 1's pulse, regardless of whether it is 1.0 ms, 1.5 ms, 1.75 ms or 2.0 ms, and it remains at its original width unless Channel 2 is varied at the same time as Channel 1. This control scheme is known as pulse width modulation (PWM).
Radio Control System Servo Waveform
Posted April 26, 2010