Mixing PID loops

[Patrick]

Id like to control pitch and yaw using PID loops but I dont know how to "blend" them for common control surfaces. The plane ill be using has two "tailerons" both responsible for pitch and yaw seen  in the following attachment.

Can it be as simple as running two independent PID loops, then linearizing the two results in micro controller memory and output to each motor by using percentages of physical travel?

[TMaxElectronics]

I guess you could just add the two output results together, but you'll have to make sure the system is stable and the two loops don't throw each other off.
Calculating that hard enough for me when using simple motors with intertia and a single PID, having two PIDs and control surfaces will be even harder I assume.

[Twospoons]

I agree with TMaxElectronics: just add the resulting actuator signals.  A properly tuned PID should be robust enough to deal with any funnies.  I would be inclined to make one of the PID loops slower than the other though - I have no math to back this up, just a gut feeling that its going to be more stable that way.

[Patrick]

Ok Im thinking of adding and subtracting for direction then multiplying by less than 1.0 for scaling the actual throw. One website for 2.4.8 Ardupilot seems to suggest a v-tail command that does this by means means of :

( https://ardupilot.org/plane/docs/guide-vtail-plane.html )

"Mixing Gain:

The MIXING_GAIN parameter is critical for vtail aircraft. It is the gain used in mixing between yaw and pitch output and the vtail movement. For example, if MIXING_GAIN is 0.5, then the following outputs are used:

    LEFT_VTAIL = (yaw+pitch)*0.5
    RIGHT_VTAIL = (-yaw+pitch)*0.5

Adjusting the MIXING_GAIN controls the percentabe of throws from pitch vs yaw."

And pics of the real one and myself, and yes it's huge !