Autotune falls out of sky

ArduPlane VTOL Plane
1

I’m trying to autotune my aircraft, its flies fine in all modes but i want to tighten it up as it is sluggish in pitch and yaw. I followed all the steps in the Quaplane VTOL tuning guide (https://ardupilot.org/plane/docs/quadplane-vtol-tuning.html?highlight=tuning). Then i did an autotune starting with roll, that went fine and roll is nice and tight now. I went to pitch next and it did not go well, after two twitches it seems to have lost power and fell to the ground, even with me inputting full throttle. No damage, the next day i tried yaw just to see if it was only the pitch axis with the issue. The same happened, after 2-3 twitches it started to descend and could not catch itself, even with full throttle. Only way to stop the descent is to switch to Q_Stabilized and go to full power.
Its not a battery issue as it flies fine, hovers at approx 50% and i used the same battery for the roll axis tuning. Any help would be great, thanks. Link to log below.

https://drive.google.com/drive/folders/1xUt7-8P6xWJUXZduTMYy_t89jNilBvUa?usp=sharing

2

I haven’t yet seen the reason for loosing altitude during autotune, but maybe start with some of these to get closer to a better tune before trying Autotune again.

Probably start by making your Q_A_RAT_PIT PID’s the same as Q_A_RAT_RLL PIDs, or at least up to:
Q_A_RAT_PIT_P,0.375
Q_A_RAT_PIT_I,0.375
Q_A_RAT_PIT_D,0.018

Try increasing Q_A_ANG_PIT_P to 5.5 or more in steps, and Q_A_ACCEL_P_MAX,36000

Change all your Q_A_RAT_x_FLTD and Q_A_RAT_x_FLTT to 15 in keeping with your INS_GYRO_FILTER,30

Found it:

image
image1332×287 73.9 KB

Motor 7 is going to maximum and the others are reasonably high too - this is not leaving enough headroom for proper attitude control while maintaining altitude.
So the conclusion is underpowered/overweight. The changes I mentioned previously probably still need to be done anyway.

3

Thanks, I’ll try those numbers.

Motor 7? It’s a quad, 4 vtol motors and 1 forward motors.

Also, how can it be underpowered if it hovers in q_stab at 53% throttle?