Inav 8.0 RC3 Airplane bumpiness

[kasatka60]

Copied the settings (diff all) from inav 7.1.2 and pasted them into inav 8.0 RC3.
In navigation modes the plane flies unstably.
https://youtu.be/n69w9CDaM8Q
(OSD is a little out of sync)
There is no SD card on board.
Maybe I configured something incorrectly when transferring the settings?
INAV_7.1.2_cli_DOLPHIN_20241215_124916.txt
INAV_8.0.0_cli_DOLPHIN_20241215_150820.txt

[breadoven]

Try adjusting the following settings which may be affected by changes in 8.0:

set nav_fw_pos_z_p = reduce to 30 or lower
set nav_fw_pos_z_i = probably OK as default
set nav_fw_pos_z_d = probably OK as default
set nav_fw_alt_control_response = new setting, could be increased closer to 40

See also #9471.

[kasatka60]

Okay. I'll try to check in a week, weather permitting.

[kasatka60]

It would be nice to add this description when switching from previous versions to the new one.

[kasatka60]

Are these universal settings or do have to select the settings for each aircraft yourself?

[breadoven]

It would be nice to add this description when switching from previous versions to the new one.

Yes, it seems to have been missed and should be added, probably to the Important Changes section @mmosca.

Are these universal settings or do have to select the settings for each aircraft yourself?

Hard to say. I've used the same settings as yourself for PID on a conventional plane and flying wing and not really noticed any pitch instability. I also increased nav_fw_alt_control_response to 50 without issues, just better altitude change response. Others have had bad instability like yourself. It might depend on other setting affecting pitch as discussed in #9471.

[b14ckyy]

Before we merge the changes in #10541 I would really like to see a blackbox log of that flight.
The frequency of the oscillation looks to me like a too high FF on pitch, that can be the result of a bad autotune or too much control surface throw resulting in a stall during autotune. Especially the Dolphin with its swept forward wings is sensitive to that.

I am hesitant to change the altitude PIDs too low as usually no one tunes them afterwards and too soft values can result in issues with WP missions or Autoland.

[breadoven]

Before we merge the changes in #10541 I would really like to see a blackbox log of that flight. The frequency of the oscillation looks to me like a too high FF on pitch, that can be the result of a bad autotune or too much control surface throw resulting in a stall during autotune. Especially the Dolphin with its swept forward wings is sensitive to that.

I am hesitant to change the altitude PIDs too low as usually no one tunes them afterwards and too soft values can result in issues with WP missions or Autoland.

The current altitude PIDS are for altitude control based on position though whereas the altitude control in 8.0 is now based on vertical velocity instead. It uses the same PID controller but with velocity error rather than position error. The basic PID tuning factors:

inav/src/main/navigation/navigation.c

Line 4961 in 4389286

navPidInit(&posControl.pids.fw_alt, (float)pidProfile()->bank_fw.pid[PID_POS_Z].P / 100.0f,

were corrected to take account of this by changing them from 10 to 100. This is based on the technical difference in required values that falls out from switching from position to velocity and also on what seemed to work from testing. The basic tuning factors weren't fine tuned any further. So it's likely the current default PIDs could be better tuned compared to previously. Reducing P fits in with what @Jetrell found from testing and others so it shouldn't be too much of an issue. It would be useful if @kasatka60 could test with lower P values to see if it helps fix the issue in this case confirming this is what's wrong. Is the Dolphin a bit pitch sensitive, seems to be the plane that others have had issues with ?

[kasatka60]

Before we merge the changes in #10541 I would really like to see a blackbox log of that flight. The frequency of the oscillation looks to me like a too high FF on pitch, that can be the result of a bad autotune or too much control surface throw resulting in a stall during autotune. Especially the Dolphin with its swept forward wings is sensitive to that.

I am hesitant to change the altitude PIDs too low as usually no one tunes them afterwards and too soft values can result in issues with WP missions or Autoland.

Inav 7.1.2
set fw_p_pitch = 15
set fw_i_pitch = 5
set fw_d_pitch = 5
set fw_ff_pitch = 231
Flight on version 7.1.2. No problems with pitch.
https://youtu.be/BA9YSCzN8ro (no osd)
I'll try to fly with the black box this weekend. Weather permitting.

[b14ckyy]

Alright guys in this case lets see the blackbox and @kasatka60 ideally you fly with current values one more time, then with the changed values as breadoven said. Just to 100% exclude any PIDFF tuning issue. Its the fast oscillation in your clip above that throws be off a bit. Especially as no one else noted that issue so far.

If the new defaults for vertical velocity pids work well and don't lack of precision (it would be bad if we have a 5m altitude error that takes 1km to correct), I am fine. I wish I had known about the necessary default changes to do more focus testing beforehand.

[Jetrell]

@kasatka60 Just inquiring. Did this value fw_ff_pitch = 231 come from an Autotune ? I'd be interested to know the setting value you have for pitch_rate. My Dolphin's FF is nothing like that high... What @b14ckyy has said does have validity.. Incorrectly tuned pitch FF and rate will certainly add to the effect.

it would be bad if we have a 5m altitude error that takes 1km to correct

@b14ckyy Lets not loose track of the fact this controller operates on a different method.. No need for the sarcasm. Its disrespectful towards @breadoven's work.
When tuned correctly, It acquires the target more quickly and doesn't experience the same initial altitude overshoot the Z position controller did.

[b14ckyy]

Sorry it was not meant to be sarcastic. Just somewhat exaggerated. I understand that the method needs new values. I just want to mess these defaults up based on a plane that is completely out of tune elsewhere and make it worse for everyone else.

I am all in for good values but they should be flown and tested on at least well autotuned planes. Then we can still tweak them somewhat conservative from there. But they should not cover up a completely messed setup.

[kasatka60]

@kasatka60 Just inquiring. Did this value come from an Autotune ?

Values ​​obtained as a result of autotune.

[Jetrell]

Thanks @kasatka60
The pitch feedforward on my two Dolphins are 90 and 110. Derived from autotune...
But our control throws would have to be different, as would have been the airspeed/throttle the autotune was conducted at, to see such a large difference between our two settings.

Being that autotune can set such a drastic difference in feedforward and likely rates too, on the same model, is interesting to see. That would mean any small oscillations from over tune of the nav_fw_vel_z controller gain, would be essentially increased by the stabilization controller with a less than optimal feedforward and rate tune.