This have nothing to with speed primarily ... speed is secondary & comes from that the AC pitch nose down. And this can't be imitated with motors off if I'm remembering it correctly from my own tests with the
MA1.
The problem for the
Mini2 is enlarged as it can pitch nose down up to 40 degrees which is much more than both the Mini1 &
MA2, and at the same time the
Mini2 only have the possibility to pitch up the gimbal with 20 degrees.
Mini1:
Max AC pitch down 20-30 degrees
Max gimbal up pitch 20 degrees
Difference Normal:0 Sport:-10
Air 2:
Max AC pitch down 20-35 degrees
Max gimbal up pitch 24 degrees
Difference Normal:+4 Sport:-11
Mini2:
Max AC pitch down 25-40 degrees
Max gimbal up pitch 20 degrees
Difference Normal:-5 Sport:-20
As seen above both the Mini1 &
Air2 manage to make AC pitch for the normal flight mode without maxing out the gimbal up pitch.
But furthermore ... both the
Air 2 &
Mini2 can utilize more than the specified AC pitch down for their normal modes (up to max for Sport mode) if going into a headwind which possibly makes this phenomenon more unpredictable for those models as this means that the gimbal drop can be seen even in normal mode there if flying into a headwind. ... the Mini1 doesn't have that capability & the problem nearly always occur only in Sport mode.
Example scenarios from flat hovering ... to forward flight until the Mini2 drops the gimbal & back to flat hovering ...
1.Hovering totally flat with AC pitch 0 degrees & gimbal 0 degrees relative horizon.
2.AC pitches forward 20 degrees for a moderate (not full) speed forward, gimbal now resting on max up tilt relative AC but still is on 0 degrees relative horizon.
3.AC goes full speed forward in Sport mode & pitches down to max 40 degrees. The gimbal can't stay leveled with the horizon anymore ... it will be turned down with 20 degrees (AC down 40 - Gimbal up 20) & are now directed 20 degrees below the horizon.
4.After this the AC returns to a flat hovering with 0 degrees pitch ... but now the gimbal still is positioned 20 degrees below horizon & needs to be raised manually. This behavior to have the gimbal remaining at the lowered position is most probably deliberatly chosen by DJI in the firmware ... this to minimize the amount of times that the gimbal is moved automatically. If the gimbal should have been returning automatically it would be jumping up & down constantly if the AC was moving around those 20 degrees pitch ... which isn't desirable at all, better with one gimbal jump down & no more.
If anything in these above described scenarios for your
Mini2 is different, then you may possibly have something fishy going on ...
And also ... this the same problem happens if you have the gimbal tilted full down (90 degrees relative horizon) ... flying forward & stop. Just when the AC breaks by pitching back, nose up ... the gimbal will be moved up towards the horizon, & it's needed to manually move it fully down again.
Hope you can see the logic behind all this ... & understand that this problem coming from mechanical limitations is much less pronounced for the Mini1 & the
Air 2.