V-tail with split control surfaces

Hey Ardupilot-Community!

On a v-tail I have split control surfaces on each side, so four in total. The two servos on each side are mounted opposite each other, so they require reversed signals.
I tried using the vtail mixing option on arduplane 3.7.1, with the elerudders on channels 2, 4, 6 and 7, with 2 and 4 being the normal elevator and rudder channels and 6 and 7 being a reversed elevator and reversed rudder.
The vtail mixer however only affects the channels 2 and 4 and not all “elevator” and “rudder” output channels, so half the surfaces in the tail are not acting as a vtail.
The .param file is attached.

Is there a way to elegantly fix this in the software? I’d like to avoid using extra hardware like servo reversers or external vtail mixers if possible.

Thanks for the help!

vtail_split.param (11.3 KB)

From your param file, I notice that RC5_FUNCTION = 4 and RC6_FUNCTION = 19. I believe 4 is “Aileron” and 19 is “Elevator”. Based on this, I’m not surprised that Channel 5 didn’t move at all. But I am surprised that Channel 6 didnt… and I personally don’t know why. Can someone else chime in?

Would you try changing both RC5_FUNCTION and RC6_FUNCTION to 24 (Rudder) and see if that gets them moving? I am not sure that it will help, but it’s the first thing I might try, to see what happens.

thanks for the quick response huntûr!
I was too sloppy in my original post, I meant channels 6 and 7 (corrected now).

servos connected to 6 and 7 moved, but only separately when the respective control surface was commanded. 2 and 4 both move when either control surface is commanded thanks to the mixer.
when I set KFF_RDDRMIX to e.g. 0.1, I can see a significant difference in how much ch.2, the elevator from the mixer, and ch. 6, the other elevator move (and with the rudder respectively the same). looks very much like 6 and 7 are just direct feed throughs of rudder and elevator commands.

Why not using differential spoilers and 3.8.0beta ?


SERVOn_FUNCTION 16,17,86 and 87


I think ArduPlane 3.8 made some changes to the RC/Servo functionality. If you’re willing to upgrade to 3.8, I recommend that approach over trying to figure out if 3.7.1 can provide the V-Tail behavior you want. (without additional hardware, of course)

Interesting idea @Rolf! The problem is, that it involves using elevons. I however have normal ailerons on my wings but don’t want my tail surfaces to deflect on a roll input.

I’ll take a look at that @hunt0r, thanks! Not too comfortable flying a beta, but we’ll see :slight_smile: