How to assign a receiver channel as a pass-thru Pixhawk ?


I would like to configure two radio channel of my receiver to pass-through Pixhawk on its RC aux channels (that is the RC9 to RC14 aux PWM outputs).

I found in mission planner the RCx_FUNCTION parameter which allows to define that RCx will be used as a pass-through output. But the question is how do you allocate which receiver channel will be passed through it ?


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  • None of the RCX pass through can be mapped to Aux ports. Pass through is only available to motor outputs. So if you are not using some of your motor outputs you can pass through a transmtter channel to the corresponding motor output. For instance channel 7 to RC7.

    The Aux ports work with the gimbal option page where you can map across. Channel 7 could be mapped to Aux10.

    • Are you quite sure about that? I have RC Passthrough working perfectly on AUX3 and AUX4 on my Pixhawk, fed by SBUS channels 11 and 12, correspondigly.

  • Hugues, unfortunetely not all receivers support that. For example Futaba R6303S has 3 PWM outputs and one SBUS. You get 8 or 10 channels via SBUS while direct PWM outputs you have a choice of different channel groups on output1 and output2 for example CH1&CH4, CH2&CH6 etc. (Output3 always reserved for CH3). Those receivers that support output both at SBUS and PWM and have 8 PWM channels, they cost twice as much as the above mentioned receiver.

    Thats why using passthrough can help "keep the costs down" and besides it is nice to use features that are available in Pixhawk. :)

  • Huges,

    Thanks for quick reply! I think what I have missed is Arming the Pixhawk, I did not think it was neccessary. Will give it a try.

    Regarding powering of Pixhawk's servo rail, do I really need to do it since I only want to take out a PWM signal out of it?

    If yes then I guess the GND between Pixhawk's servo rail must also be connected to the Gimbal controller's GND, which I already have. Is that correct?

    • MR60

      If you just want the signal, why go through pixhawk then? Couldn't you more simply use two free receiver's PWM outputs directly to your application ? (I do not know futaba receivers but with FrSky receivers you get both the SBUS output and individual outputs simultaneously)

    • Not all receivers do this. For example, the FrSky X4R-SB only outputs CH1-3 and SBUS.

    • If you only need a PWM signal from the passthrough outputs, you don't have to connect servo rail power. And yes, you need a ground connection alongside the PWM signal between the Pixhawk and the gimbal controller.

  • A little late to the party, but this was one of the main results as I googled for the same problem, so I thought I'd post my solution here.

    RC Passthrough works fine for me on the Pixhawk running APM:Copter 3.2, for SBUS input channels 9-14 directly mapping to AUX 1-6. For 9-12, all I had to do was set RC_##_FUNCTION = 1 for the corresponding channels. For 13-14, BRD_PWM_COUNT needs to be set to 6 to enable AUX 5 and 6, then also RC_13_FUNCTION and RC_14_FUNCTION to 1 and voi-la.

    Additionally, I'm using channels 9-11 for gimbal control now instead of passthrough (pan, tilt, and roll connected to "mode" input of my BLG). This can't be configured in the normal Mission Planner Gimbal Settings GUI directly. What I did was configure outputs (RC9, 10 and 11) in the Gimbal Settings, and then set the input channels in the Full Parameter Tree - MNT_RC_IN_PAN (_ROLL/_TILT) to 9, 10 and 11 as needed. Check that MNT_MODE is set to 3, as well, otherwise it won't respond to RC commands.

    Hope this helps someone with the same issue.

    • This did help me indeed, thanks Olex ... :-)

    • Hi

      I have a R6308SBT receiver connected and working fine with Pixhawk via SBUS. I want to passthrough channel 7 or 8 and connect it to my gimbal input pins to control the pitch of my camera.

      Still struggling to make this work on my Pixhaw, but no success yet. I cannot understand which of the RCx_FUNCTION are mapped to which AUX output on the Pixhawk? Please help!

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