Pitch back non-volontary


I have issues with my drone when I give constant tilt (roll or pitch) during a few seconds, the drone tilts back!
For example, I pitch front to go forward and after a few second it pitch back and then again pitch front as desired. I don’t know why it pitches back. There were no external perturbation (no wind).
Here is the log: https://review.px4.io/plot_app?log=6f6af0f2-27f3-47de-99df-fc0df1058fce


Hi @alexcherpi

I have the impression that this is related to your frame, like if there was some aerodynamic effect that creates a pitch up torque: the controller produces a downward pitch control signal that goes through the allocator and sets the two front motors that ramp down to their minimum value while the rear ones ramp up until saturation but the drone still pitches up. At the same time you have a roll error (roll-pitch coupling?)

Are you really flying a quad? Do you have aerodynamic surfaces or heavy spinning rotors (gyroscopic effect) or an asymmetric drone (large inertia cross-coupling) ? I also see that you have extremely large integral values, which shows that it isn’t a standard setup (or that you changed the PID architecture).

Furthermore, during that time the drone doesn’t climb nor descend (stays at 121m ?? wrong measurement ?)

Note on the side: I can also tell you is that you have a constant negative yaw offset. A yaw offset with a nonlinear PWM-to-thrust curve produces roll-pitch coupling. Some ESCs try to linearize that curve, others don’t.

Hope that helped, maybe I can give you more help if you tell us a bit more about the drone.

Good luck!