Plane: add option to use boost motor in forward flight, tiltrotors and tailsitters only

[IamPete1]

This gives the option to use the boost motor in forward flight, this is actually an improvement because currently the boost motor can be used in Q modes but just stays at its last value in forward flight. This fixes that.

Tested with a Realflight model from Fanman

https://discuss.ardupilot.org/t/new-tricopter-quadplane-concept/47469?u=iampete

[kd0aij]

LGTM, I tested in RF8 and the boost motor seemed to work correctly in qhover and fbwa

While this shouldn't affect tiltrotors and MatrixTailsitters if the q_option bit isn't set, I assume this hasn't been tested for those cases.

[IamPete1]

@kd0aij I tested on a tiltrotor, it works as it should. The user wants the boost motor to be the only tilting one. Should work for tailsitters also although not tested myself.

I put this in for MatrixTailsitters also but I think in that case its actuality not useful because I'm not sure if they output the boost motor in hover in the first place.

[Fanman74]

Checked all modes, FBWA, QHOVER, Stabilize, Manual & QRTL. SITL model behaves as expected.

[kd0aij]

I had forgotten about this PR... This brings up a question as to why the "boost" motor wasn't handled by just adding it as a separate frame type, so that the motor mask could be used to enable/disable it in forward flight. The disadvantage would be that you would have to add a frame type for every motor configuration (quad/hex/etc). But then use of the boost motor could be more sophisticated; instead of a static boost scale factor, output_armed_stabilizing() could include the presence of a boost motor in its calculations, perhaps enhancing stability when a motor is lost.

[kd0aij]

I think you only need the new options bits and argument to output_motor_mask because the boost motor isn't in the logical motor_mask. Perhaps there's a better way to do this... maybe add a new frame type which includes the boost motor. Then you would also have a way to specify whether or not the boost motor tilts (and is active in forward flight) using tilt_mask. It might be a good idea to add a separate mask to indicate which motors are active in forward flight too, if there is ever a case in which non-tilting motors should remain active.

[IamPete1]

we should probably also convert the param uint16_t. Currently if you have a boost motor it is always output in hover and this gives the option to also output it in forward flight. Not a fan of doing new mixers, then we have to do a new one each time. This supports all frames.

I will re-base this and see how its looking

[kd0aij]

There's a bug in AP_MotorsMulticopter::output_boost_throttle() too: if you change MOT_BOOST_SCALE to zero, the boost motor keeps running at its last value.

[IamPete1]

rebased

[IamPete1]

I don't remember the use case for this, it conflicts so I'm closing.

[Fanman74]

What is the conflict? have been testing the boost motor for the forward flight propulsion unit.

[IamPete1]

@Fanman74 There were file conflicts, this would need a little work to rebase on master.