EPA, does it affect the esc?

[BrianG]

I find that if you understand how a radio works, you can easily answer these types of questions so they make logical sense. These observations were noted and measured using an oscilloscope.

Each channel on the output of a radio receiver consists of a series of squarewave pulses. This is the same no matter what type of transmission medium it uses: AM, FM, PWM, DSS, etc. The pulses occur at a rate of one every 20ms (approximately), which equates to a frequency of 50Hz (again; approximately). The actual frequency is not really that important as long as they are consistent, repetitive, and frequent enough to be a valid signal. Typically, each pulse is "on" from 1ms at minumum servo throw to 2ms maximum servo throw. Servo "center" would be 1.5ms.

Incidentally, this is how failsafe devices work; they look at the consistency and repetitive qualities of the pulses to determine of they are valid and not just "noise". If not, it ignores the errant input signal and synthetically creates an appropriate pulse to send to the servo/ESC to cause it to go to failsafe position. But I digress.

When you increase your endpoints, you decrease the min to a little below 1ms, and increase the max to a little above 2ms allowing for a greater servo/ESC range. Decreasing your endpoints increases the min to a little above 1ms, and decrease the max to a little below 2ms allowing for reduced servo/ESC range. Adjusting the center varies the signal a little above/below 1.5ms. When I say "a little", I mean like 0.05ms (50us) or even less. Reversing the output switches the min and max signals, causing the maximum to be 1ms and the minimum 2ms instead, just as the term "reversing" applies.

So, for throttle, full forward would be 2ms, full brake/reverse would be 1ms, and neutral would be 1.5ms. Increasing the EP to, say 110%, would make the signal go below 1ms and above 2ms for more servo range. Decreasing it to, say 90%, would make the signal stay above 1ms and below 2ms for less servo range. Then the various positions in between would vary linearly between these measurements. Reversing the servo signal on the transmitter would put full forward at 1ms and full reverse at 2ms instead.

The steering channel works in a similar fashion; full left=1ms, full right=2ms, and center=1.5ms. As stated, these values can be adjusted a little based on servo centering, reversing, and EPA.

On some radios, you can set an exponential response curve so that there is little change when you move the control near the center position, but changes more as you move the controller towards the max/min positions. This would allow for more precise control near the center, which might be especially nice for steering at high speeds, or low throttle for rock climbing.

The servo or ESC takes these signals and, along with device programming, converts them to something it can use. So, the part that decides whether to brake or go into reverse is actually in the ESC. It just looks at the pulses coming from the radio receiver and the speed of the motor and decides what to do.

EDIT: Edited for accuracy and readability :).