Investigating pitch setpoint tracking issue

[YohanHadji]

Hi there,

Using INAV 7.0.0 I have experienced a weird behaviour flying in ANGLE mode which only happened twice in 6 months (and 50+flights) and can't reproduce:

At the beginning of the flight the pitch setpoint is tracked perfectly, but as time goes (flying 15~30min) a given pitch setpoint results in a larger and larger tracked pitch. As if some integrator somewhere was doing something unwanted.

• Continous servo trim feature is disabled
• AUTO LEVEL TRIM mode is disabled
• SERVO AUTOTRIM mode is disabled

The only hint I have is that the error gets bigger and bigger with time AND switching to a different PID profile instantly change how wrong the tracked pitch angle is. For example, when switching PID profile every 30sec for the whole flight:

• At the beginning of the flight, pitch is tracked perfectly for both PID profiles 1 and 2.
• After 30 minutes tracked pitch is 1.5 times higher than it should be for PID profile 1 and 2.0 times higher than it should be for PID profile 2. When switching between the two PID profiles the transition is instantaneous.

Just looking for ideas of areas to look at. My questions for the community are:

• What do you think I could deduce from the fact that switching PID profiles changes the tracking error while I have no tracking error at the beginning of the flight?
• Is there any way to double check that no trim mode is actually active even though it's clearly showing as not activated from the CLI?

Here are the potentially related issues I've been able to find, but it seems like it shouldn't be related because I don't have any trim feature activated:

#9912
#10575
#9637

Two attached pictures, in red the PID profile used, in blue the measured (tracked) pitch, in yellow the pitch setpoint (just to show the steps are not coming from the setpoint but from the change of profile).