Inav: Add 'automatic servo trim' for fixed wing

[Painless360]

At the moment the trimming of the servos can be done using the Servo Autotrim function. While this works well there is a feature in ArduPlane that I use a lot that does this automatically fro the pilot (https://ardupilot.org/plane/docs/auto-trim.html)

The automatic autotrim function monitors the value of the servo channels needed to keep the model in the level attitude and then updates these refined middle channel positions for the elevators and ailerons at a regular interval. This is very handy if you set up the model with a slightly different CG - the model trims itself automatically.

The idea is to add this feature to iNav and have it settable as 'always on' so that iNav can perform the same kind of function.

This would make it easier for all fixed wing pilots to have the plane auto-trimmed for level flight without having to do anything and a short flight in a flight stabilised mode would set the servos for a great manual flight too. Every flight.

Thank you for your consideration, I've looked for this suggestion in the Wiki but didn't find it so apologies in advance if you already have this on the list somewhere... Happy flying!

[Jetrell]

This would be a great feature.
@digitalentity Would the AHI / Accelerometer drift bug cause such a feature to be unreliable at present?

[digitalentity]

Trimming is essentially "flying stable in a certain position" and I-term does exactly that dynamically. We might want to add a very slow integrator on top, to actually "trim" servo middle points in flight all the time. I don't think AHI drift will be relevant as long as we don't trim for a "level flight" specifically.

Also IMO "level flight" is unrelated to servo endpoints and more related to FC alignment (pitch specifically). From FC perspective we might be flying level, but we might be actually climbing or sinking because of incorrect angle of attack. Trimming FC pitch alignment is somehow non-trivial, but IMO doable.

[FPVZaphod]

In my very fast planes (Strix Goblin and SAB Tortuga) I fly 90% of the time in manual mode, because I love to "feel" the plane. iNav is for the home arrow, and bring the bird back home in worst case.
I was thinking already to program my radio in a way that in manual flight mode the radio trims are active, but not in all other flight modes. Working solution, but I would prefer to have the option to trim the plane in iNav. Two new options in "Adjustments", "Trim Roll" and "Trim Pitch".

[myrcwing]

What the original poster mentioned would be a great feature to have for many fixed wing pilots. I second this