Lua Script for copter CoM compensation

[Georacer]

This PR is a script that corrects for the CoM discrepancy in a quad-X frame. It is applicable both in Copter and (quad)Plane.
I guess it's what #17461 was envisioned for.

It uses the dynamic mixer matrix to update the front-to-back thrust ratio on the fly.

I've been testing with RealFlight on this model, after "bringing it close to reality" by reverting the "cheat" I had made in the motor positions:

The issue with this model is that due to the CoM misplacement, a throttle-up causes a pitch-down. The script corrects the buildup of the pitch I-term and suppresses the pitch-down motion upon throttling up.

The results have been documented in this blog post.

If you think this script is too dangerous to exist in the applets directory, I'm happy with it being in the examples too.

[IamPete1]

Dynamic mixer is great for finding the correct value, but it would be nice to transition people onto the normal mixer. Then you can just have a script that runs at boot with no callbacks. I think the load_factors call skips the normalization step that we do on a "normal" matrix. So there could be some change in tune.

[IamPete1]

Suggested change

	return protected_wrapper()
	return protected_wrapper()

[IamPete1]

You might as well call this directly

[Georacer]

Dynamic mixer is great for finding the correct value, but it would be nice to transition people onto the normal mixer. Then you can just have a script that runs at boot with no callbacks. I think the load_factors call skips the normalization step that we do on a "normal" matrix. So there could be some change in tune.

@IamPete1 A static mixer would definitely bring better performance, agreed. But I really wanted to be able to tune on the fly.
How does the idea that I modify the present script so that it switches between dynamic and static based on a parameter sound?

[IamPete1]

@IamPete1 A static mixer would definitely bring better performance, agreed. But I really wanted to be able to tune on the fly.
How does the idea that I modify the present script so that it switches between dynamic and static based on a parameter sound?

You could check if you can see the Motors_dynamic or AP_MotorsMatrix singletons so it would switch based on frame class.

[tridge]

this is so common that I wonder if a param in the C++ code is warranted?

[Georacer]

this is so common that I wonder if a param in the C++ code is warranted?

You mean skip the .lua script entirely and implement this in C++? If so, I'd like to have this merged first and then dive into those deep waters 😅.

[Georacer]

Dynamic mixer is great for finding the correct value, but it would be nice to transition people onto the normal mixer. Then you can just have a script that runs at boot with no callbacks. I think the load_factors call skips the normalization step that we do on a "normal" matrix. So there could be some change in tune.

How about I add the normalization step to the AP_MotorsMatrix_Scripting_Dynamic::init() as well?

[IamPete1]

this is so common that I wonder if a param in the C++ code is warranted?

Using throttle factors does add some inaccuracy in the mixer. We do the full mix and then apply throttle factors afterwards, so there not taken into account for the saturation handling. Unless there is a quite significant issue its probably better not to set them and I would not recommend large values at all. As ever, a hardware fix is better if possible.

How about I add the normalization step to the AP_MotorsMatrix_Scripting_Dynamic::init() as well?

You would have to do it on every call to load_factors. I think its fine that the dynamic mix doesn't do it automatically. You could add it in the script. They thing is that if you do the normalization then you can use the same mix with both scripting mixers.

[Georacer]

@IamPete1 A static mixer would definitely bring better performance, agreed. But I really wanted to be able to tune on the fly.
How does the idea that I modify the present script so that it switches between dynamic and static based on a parameter sound?

You could check if you can see the Motors_dynamic or AP_MotorsMatrix singletons so it would switch based on frame class.

@IamPete1 is this what you meant?

    if MotorsMatrix then
        is_mixer_matrix_static = true
        warn_user("Found static mixer", MAV_SEVERITY.INFO)
    end

This check follows the truthy path even if Q_FRAME_CLASS=1.
Did you have another check in mind?

[Georacer]

@IamPete1 I've pushed another another version.

I've managed to implement dual operation, both dynamic and static scriptable matrices.
The switch is done via the [Q_]FRAME_CLASS parameter. I wasn't sure how to achieve it via the singletons.

Both use the same factors, normalized to have max 1.

I've tested it in RealFlight. Some examples:

When Q_FRAME_CLASS=1:

Operation in Q_FRAME_CLASS=17:

Operation in Q_FRAME_CLASS=15

Do you require any more specific testing?

[Georacer]

Got another update in, to delete two unused variables.
For some reason run_lua_language_check.py didn't catch them.

❯ ./Tools/scripts/run_lua_language_check.py libraries/AP_Scripting/applets/x-quad-cg-allocation.lua
Initializing ...
>>>>>>>>>>========== 1/2
>>>>>>>>>>>>>>>>>>>> 2/2
Diagnosis completed, no problems found
2 Files checked

[IamPete1]

I wasn't sure how to achieve it via the singletons.

I think you can just see if the singleton is nil. Something like:

if Motors_dynamic then

else if AP_MotorsMatrix then

end

For some reason run_lua_language_check.py didn't catch them.

Yeah, it doesn't get everything. The other one, run_luacheck might get them tho.

[Georacer]

I think you can just see if the singleton is nil.

I had tried the following before, but I believe was getting exceptions.

-- Decide if the UA is using a static mixer matrix.
function inspect_mixer_matrix_static()
    if MotorsMatrix then
        is_mixer_matrix_static = true
        warn_user("Found static mixer", MAV_SEVERITY.INFO)
    end
end

-- Decide if the UA is using a dynamic mixer matrix.
function inspect_mixer_matrix_dynamic()
    if Motors_dynamic then
        is_mixer_matrix_dynamic = true
        warn_user("Found dynamic mixer", MAV_SEVERITY.INFO)
    end
end