Losing altitude while changing flight modes

Hi all,

I’m flying a pretty big X8 copter (~16Kg) with copter 3.5.0rc4 and i’m experiencing weird behavior while changing flights modes from stabilize to a climb_rate controld flight mode like Loiter or AltHold.

The throttle on stabilize is set to about 50% (MOT_THST HOVER=0.44) so when changing flight mode we are still in the deadzone area.

I’m attacing a flight log, all we did is flying in hover and change flight modes, you can see the drastic change in ch_out motors and the climb_rate. After the copter drop about 2-3 meters I think is settling down so the real issue is understanding why the throttle lower itself so bad while hovering?

Can really use a help with this.

Thanks, Gal.

Your logs show that whenever you switched from Stabilize to Loiter/Althold, the copter would always ascend slightly before descending. Is this what you observed?

From what I can tell, the copter is commanding a throttle down because it senses that it is ascending. If the ascent was not observed, that would suggest a problem with climb rate estimation, which is usually a symptom of vibrations, although your vibes are good. If the ascents did really happen, then there is something else going on.

This is normal behavior when you switch between loiter to and stablize or althold. Over time it will diminish if you set MOT_HOVER_LEARN to 2.

As far as I understand MOT_HOVER_LEARN in autolearn only changes MOT_THST_HOVER so it will be in the middle of the pilot stick.
I Tried different values of MOT_THST_HOVER from 0.2-0.8 and in all of them the vehicle losses altitude.

I don’t think it’s related to MOT_HOVER_LEARN or MOT_THST_HOVER.

Don’t know still why but after replacing the autopilot (mini), the issue solved.