Discussions

Hi Droners.  I've implemented V-tail mixing support in ArduPlane 2.68.  I chose 2.68 rather than 2.70 as I am not using the PX4 board.  Previously, if you were using a V-Tail model you have to use an external V-tail mixer.  If you've tried an external V-tail mixer you will know they can be laggy and sometimes unreliable.  Hence, I roll up a first pass of the V-tail firmware. 

At present it's implemented as a couple of pre-processor directives that you set in APM_Config.h.  I'd like to make it more future-proof by making it a config parameter that can be tuned via the MissionPlanner.  However, I'd like to get it out so that other people who might want to use V-Tail mixing can test it. 

To implement it, I de-mix the V-tail mixing in the read_radio() function and re-mix it in the set_servos() function.  This means that internally, the APM thinks you have a regular elevator/rudder tail.  It also means that if the APM should crash, the PPM hardware should pass your signal through to the servos. 

I've flown it in one model, 3 flights.  It performed flawlessly in MANUAL, STABILIZE, FBW_A and RTL modes, the only modes I used.  However, it would be great if more people can test and extend the V-tail mixing.  I have one more V-tail model I'm repairing and will remove the V-Tail mixer and use this new firmware. 

To test it, please apply the provided patch (VEE_TAIL.patch) to ArduPlane 2.68: 

cd ArduPlane-2.68/ArduPlane

patch -u < ../../SourceCode-ArduPlane2.68/Vee-Tail-0.1.patch

 If you are uncomfortable using the patch command, I've included a .zip file of the modified files.  Unzip these into a clean ArduPlane-2.68/ArduPlane directory and you should be able to compile V-Tail mixing.  If you use the patch, V-Tail mixing will be enabled in your APM_Config.h.  It's not enabled if you use the .zip file, to avoid overwriting whatever configuration you've already set. 

Instructions for use are in APM_Config.h.reference (and copied below).  Going forward, I'd like to see this pushed upstream to the main codebase.  In the mean time, let's test it a bit more.  

//////////////////////////////////////////////////////////////////////////////
// VEE_TAIL_INPUT                       OPTIONAL
// VEE_TAIL_OUTPUT                      OPTIONAL
// VEE_TAIL_REVERSE_YAW                 OPTIONAL
// VEE_TAIL_PITCH_SERVOS_OPPOSITE       OPTIONAL
//
// V-Tail mixing options.
// *NOTE*: do not confuse with elevon mixing (set with g.mix_mode), which is sometimes called V-tail mixing on the forums and knowledge base.
// Set any of these options to ENABLED to enable them.
//
// Enable VEE_TAIL_INPUT to de-mix V-Tail mixing, as programmed in your RC radio.
// This enables the AP software to interpret the 2-channel V-tail mixing as separate elevator and rudder channels.
//#define VEE_TAIL_INPUT                   ENABLED
//
// Enable VEE_TAIL_OUTPUT to re-mix V-Tail mixing.
// Usually VEE_TAIL_INPUT and VEE_TAIL_OUTPUT are enabled together, unless you are testing V-tail mixing.
// In theory, if the APM crashes, the hardware multiplexer should pass through your radio's V-tail mixing as manual control.
//#define VEE_TAIL_OUTPUT                  ENABLED
//
// Enable one, or both of these next two options to get your V-Tail mixing to work the correct direction.
// VEE_TAIL_REVERSE_YAW will reverse the yaw de-mixing (and subsequent re-mixing) direction.
// Set VEE_TAIL_PITCH_SERVOS_OPPOSITE if the tail servos rotate in opposite directions for pitch control.
// Leave it unset if both servos turn in the same direction.  For example:
//
//    ____      ____       FRONT
//  __|__ |     | __|__     /|\
// (o   O |     | O   o)     |  Servos turn opposite for pitch: set
//  ----- |     | -----      |     VEE_TAIL_PITCH_SERVOS_OPPOSITE ENABLED
//    |   |     |   |        |
//    |___|     |___|       \|/
//                          BACK
//    ____      ____       FRONT
//  __|__ |   __|__ |       /|\
// (o   O |  (o   O |        |  Servos turn same for pitch: unset
//  ----- |   ----- |        |  VEE_TAIL_PITCH_SERVOS_OPPOSITE ENABLED
//    |   |     |   |        |
//    |___|     |___|       \|/
//                          BACK
//
// Getting the correct order of these last 2 settings may require some trial and error.  Here is the order of steps I suggest:
// 1) Set up V-tail mixing in your radio, and test it in your model WITHOUT the AMP (just regular control).
// 2) Hook up the APM as recommended in the manual.
// 3) Compile the firmware with VEE_TAIL_INPUT and VEE_TAIL_OUTPUT.
// 4) Test V-tail mixing in APM after it boots up.  Make sure you are in MANUAL mode.
// 5) If yaw and pitch are reversed, set VEE_TAIL_PITCH_SERVOS_OPPOSITE and rebuild.
// 6) If V-tail yaw is reversed, set VEE_TAIL_REVERSE_YAW and rebuild.
// 7) If neither of these changes works, you may need to reverse the tail servos on the OUTPUT side of the APM and go back to step 4.
// 8) Once MANUAL mode is working as expected, try STABILIZE mode.  Pick up the model and pitch up/down to ensure the tailplanes are going the correct direction.
// 9) Good luck, and please post your results on the forum!
//
//#define VEE_TAIL_REVERSE_YAW             ENABLED
//#define VEE_TAIL_PITCH_SERVOS_OPPOSITE   ENABLED

Vee-Tail-0.1.patch

Vee-Tail-0.1.zip