APM:Plane 3.3: Cannot Get Aux Output to Work

I have ArduPlane 3.3 set up on my wing, using elevon mixing. Everything works as expected. Because I am interested in adding yaw control to the wing, I am investigating using split elevons. The problem is that I cannot get the Aux pins to drive a servo.

Setting RC*_FUNCTION to some nonzero value that makes sense (16 or 17 for split elevons, rudder, ground steering, etc), and writing the configuration to the board yields no response. I am powering my elevon servos with an independent UBEC, connecting only the signal pin from the servo to the board (JP1 is not connected). When I am testing the Aux output, I am moving the servo signal pin on the "Output" rail to the appropriate Aux pin. So, this is not a servo power issue, or a bad connection in the signal wire.

Although unused, the voltage between the + and - on the Aux rail is 3.3v. Unfortunately, I do not have a scope to look at the output of the Aux signal pin.

Do I need to do something else besides change RC*_FUNCTION? Is there a "Turn on Aux Output" switch?

I have seen others commenting that the split elevon code does not always work. But, before I can troubleshoot that, I need to get some sort of response from the Aux rail (using split elevons, rudder, or something). 


[As a sidenote, the split elevon if/then section in Attitude passes a float to the Aux output, whereas elsewhere, the Aux output is passed an integer. Removing the implicit casting does not affect the non-operation of the Aux rail in the context of split elevons.]

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    • Craig, can you be more specific? I'm on APM, not Pixhawk. Honestly, I do not see any correlation between the aux pins on APM vs Pixhawk.

      But, the most straightforward interpretation is that you should be able to set up differential elevons on Pixhawk on the aux outputs 1-6 (pins 50-55). With APM, this would be aux pins 5-12.Yet, on APM, it only works on pins 10 and 11.

    • Developer

      Sorry,  I have been getting lots of questions from other people about Pixhawk and I misread.

      The Aux pins on APM are input only.  They will not drive a servo so you are limited to RC channels 1-11 for output to the servos

    • No worries. I'd like to get a Pixhawk sometime.

      I am fairly sure that you are at least partially wrong about the APM Aux pins. I can drive servos all day on #10 and 11.

      The others? Maybe those are input only?

      It seems sloppy that you can set their function to drive a servo (RC_FUNCTION), but not drive a servo. There should be different RC_FUNCTION structs for input only Aux pins.

      Thanks for your help.

    • Developer

      You can see where outputs 9-11 are on the board and then the rest of them are analog inputs.


    • Got it. I tend to miss a lot of the documentation because I am only interested in fixed wing. The rotor documentation is much more thorough. Thanks, again.

  • So, upon further investigation, I can only get channels 10 and 11 of the Aux rail to drive a servo. The others (5-9) do not work.

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