Plane pithching up and down in rth mode.

[udum6]

Hi, my plane whenever i turn on rth mode starts pitching up and down rapidly. I tried changing some pid settings but i couldnt solve the problem.I think the proplem is in pid settings but i don't know what setting to change.

inav version: 7.1
FC board: matek f405-wing v2

Here is the problem in flight:
https://github.com/iNavFlight/inav/assets/166306115/b84bfb03-816d-4d98-b65d-30ed574bcd87

[MrD-RC]

The bigger problem is that it's in failsafe, not RTH.

• How much control surface throw do you have for pitch? Is it too much?
• Do the pitch servos centre correctly? (Always to the same place)
• Is there any slop in the control linkage?
• Have you run AUTO LEVEL TRIM?

You want to check all of that before touching PIDs.

[udum6]

Ok i will try it and see if it works.

[breadoven]

Well it is in RTH but triggered via Failsafe mode I assume. If you want to use RTH just trigger RTH mode directly, don't do it via Failsafe mode. Failsafe mode is really just to check Failsafe is working as expected, it's not a mode to use normally.

[udum6]

The throw is ok and servos centre correctly. There might be a problem with my control linkage beacouse it is just a thin steel wire, its pretty stiff but it bends a little when the servo is at max throw. Also I will try to run auto level trim today.

[MrD-RC]

How much throw is max throw?

What airframe is it?

[udum6]

It is a custom made airplane. Max throw is around 1 or 2 centimeters.

[MrD-RC]

Between 1 and 2 cm. You mean it can vary between 1 and 2 cm. If so, that is a big problem. 2 cm could be a lot of throw. Depending on how big the aircraft and wing is.

[udum6]

Sorry for miss Information but today I mesured my throws to be shure. The exact value is 5mm of throw on the elevator.

[CarolineTyler]

I've had a similar issue with running a waypoint mission - see video https://www.youtube.com/watch?v=N0CbEymUxSM
Wing flies normally in manual/acro and usually in RTH / CRUISE - but I don't really use those modes often.
Had another wing flying the same mission and the issue occurred at the same point in the mission flight.

[Squirrelynutz]

I'm also getting this issue during rth and cruise. Any other flight mode is perfect
Mini drak

[breadoven]

I've had a similar issue with running a waypoint mission - see video https://www.youtube.com/watch?v=N0CbEymUxSM Wing flies normally in manual/acro and usually in RTH / CRUISE - but I don't really use those modes often. Had another wing flying the same mission and the issue occurred at the same point in the mission flight.

Which version of INAV were you using ?

[CarolineTyler]

I've had a similar issue with running a waypoint mission - see video https://www.youtube.com/watch?v=N0CbEymUxSM Wing flies normally in manual/acro and usually in RTH / CRUISE - but I don't really use those modes often. Had another wing flying the same mission and the issue occurred at the same point in the mission flight.

Which version of INAV were you using ?

7.1.1

[CarolineTyler]

Here is the HD video of this waypoint mission as it has sound you can hear the motor ramping up and down...
https://youtu.be/8JmEGEPSYs8?si=_Va6yjhtawHSnXyA
2:24 - 2:58 waypoint pitching up and down with motor ramping
4:16 - 4:48 Failsafe (I had forgotten to set the waypoint mission NOT to failsafe) The turn around and backtrack is very dodgy full of motor pulsing, then when it hits a climb the pulsing stops for a while 4:49 - 5:00 it's pulsing again in backtrack.
5:00 The plane hits the RTH altitude climb with a spiral 5:39 - plane points to home and acts normally!
7:57 - RTH starts decent to loiter at home height
8:12 - I take over control