What are the PWM direction conventions and default values?

Hello everyone,

I´m trying to do a SITL quadplane simulation and i´m sending data via the JSON format from Matlab to MAVProxy. I use the PWM output from the flight controller to calculate the values for the motors and servos. I know which channel is for each motor and servo of the control surfaces.

My Question now is which are the conventions for the servos of the ailerons, elevator and rudder? For example if the rudder is moved all the way to the right, when looking at the nose of the plane, is the PWM value for this the highest or the lowest value?

Another Question i have is where i can find the default values of the servos (min, max, trim)? If I open up …/Tools/autotest/default_params/plane.parm or quadplane.parm I can see the max, min and trim values for the RC parameters but not for the servos. Do the servo parameters have the same values as the RC Parameters?

Thanks for you´re answers in regard

PWMs typically follow the orientation of the sticks on a transmitter, with up and right being the positive directions. This leads to the following being PWM high:
Roll right
Pitch down
Throttle high
Yaw right

That said, it isn’t terribly important and in real models they often get reversed for convenience or other reasons.

For the servo PWM range, there are parameters like SERVO5_MAX, _MIN, etc.: https://ardupilot.org/plane/docs/parameters.html#servo-parameters

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Thank you for your answer!

About the PWM servo range. I´ve been browsing the complete parameter list and have seen it says “Typically 1000 is lower limit, 1500 is neutral and 2000 is upper limit”. I was wondering if i can find the exact default value somewhere. Or am i just not seeing it?

On the other hand i can still configure them myself or check what MAVProxy sends back when i change RC values to a high value maybe.

Looks like the default values are 1100, 1500, and 1900: https://github.com/ArduPilot/ardupilot/blob/plane4.0/libraries/SRV_Channel/SRV_Channel.cpp#L38-L47

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Thank you that helps a lot

The exact numbers will depend on hardware setup and trims.