Problem with RC Channel Mapping

Hi Everyone,

I have not posted here before and have been building a Trex 500 Flybarless (new 500L rotor head) as a testbed for the tradtional branch of APM.  After loading the correct firmware (V3.2.1) in the APM2 Planner, I went to calibrate the radio and discovered the RC channel order from my JR X11 (Using Orange DSM2 9Ch Rx SBUS) into the Pixhawk RCIN are not mapping to the expected as below:

The JR / Sepctrum RC Mapping
Channel 1 AIL
Channel 2 ELE
Channel 3 THR
Channel 4 RUD

What I observe instead under the APM Panner 2.0 Radio calibration display, is the following SBUS RC channel order

channel 1 THR
channel 2 AIL
channel 3 ELE
channel 4 RUD

To highlight one example.  I move the Throttle stick (Mode 1 set)  and the Roll (AIL) PWM values change in the radio calibrate display.  Even the other switch based channels (5-8) on the JR Radio do not line up.

The trouble is, the JR X11 Radio has no option to change the primary RC channel order / mapping.

I might add I have used this JR radio for previous APM2 multi-rotor flying, with no RC channel map issue.  The primary difference back then is I did not us the PPM method which is needed with a Pixhawk.

Has anyone encountered this issue or similar before? and found a way to change the received RC mapping on the APM side?

I know that open source radios like the FrSky T can change the PPM channel order and I suspect with a FrSky receiver APM is seeing the order as AETR  where as my setup is apparently seeing a channel order of TAER. Of course if I have a normal receiver the channels are correct.

Just as a side note, are there any plans or beta yet of the same "Heli Setup aids" in APM Planner 1 making there way to APM Panner 2?  With APM Planner 1 no longer updated I cannot use the old heli setup to easily observe the heli specific setup and selection of the values for the swash, swash mix and travel extents. (see the PWM values when using manual pass thru)

The bottom line is I cannot fly the traditional heli until I can get the correct channel order assignments during the radio calibration. 



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  • Greg,  I use Spektrum recievers and just had to swap a few wires with the PPM encoder to make everything work right.


    David R. Boulanger

    • @David,

      Thank you

      I do not use the PPM encoder so I have no wires to swap.  But this might be an option be it adding another component in the system.  

      The normal method for connecting the pixhawk is the single wire to the RCIN So the way it stands now is Spektrum/ JR channel ordering on the TX side is not compatible with APM.  Futuba / FrSky order is what the autopilot is expected.  I thought there might have been a way to re-alocate the channels in the APM code using parameter settings.  But I cannot find a reference so far

    • Greg,  I've been using the PPM encoder with my AR8000 receiver for some time and all is well.  I agree it adds a bit to the clutter.


      David R. Boulanger

    • David that is good to know you have been using with no issues.  I will order one today and try it as well. I have asked one of the developers a question about possibly mapping the different sequence to the correct PWM channels in APM.  I suspect it will be easier to switch to a radio with programmable Tx or open firmware which will allow the AETR versus TAER to be avoided

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