I’m having trouble trimming elevons when using the ELEVON_OUTPUT mode. I have all surfaces moving in the correct manner, my only issue is with trim.

There is NO mixing configured on the TX.

The procedure I have followed is thus,

  1. With ELEVON_OUTPUT = 0 (disabled), and in manual mode, I have adjusted sub-trim and end-points to accommodate the mechanics of the wing. In this mode I can correctly position the left and right elevons independently using aileron and elevator, and both are properly centred at centre-stick.
  2. Calibrate RC, this stores the correct neutral values in RC_TRIM, and endpoints in RC_MAX / RC_MIN for all channels, but only 1 and 2 are important here.
  3. Set ELEVON_OUTPUT = 2, now channels 1 and 2 are synthetically generated at ALL times, even in manual mode.

Unfortunately, in both manual or FBWA modes, the RC_TRIM (and presumably RC_MAX / RC_MIN) values are ignored; the elevons move to the centre-position they would have without sub-trim. Any synthetically generated output needs to be subject these tuning parameters.

Is there a setting I have missed? Or is ELEVON_OUTPUT not able to use the trim values (which would make it useless as far as I can tell, unless you are lucky enough that all your servo horns happen to align correctly).

Also, is it important which elevon (left/right) is connected to CH1 / CH2, it seems that the four modes for the ELEVON_OUTPUT accomodate either orientation.

Although it seems less correct to me, it was suggested that I try removing the subtrim and endpoint settings, and then enable ELEVON_OUTPUT, then attempt tune the settings for the elevons combined. It seems like there will be some unintended mixing between the channels, but it may just work anyway.

I had similar issues with elevons. The easiest way to sort it is to fly the plane in manual mode and get it flying straight and level on the throttle setting you’ll use in Auto mode by adjusting the elevon linkages with no subtrim or trim on the transmitter.

I don’t think it matters which elevon servo is on which channel just as long as the surfaces move in the right direction in manual, FBWA and stabilize modes.