Oscillations while descending


Specs :
Cube Orange ADSB
Antigravity MN5006
Tmotor NS18*6 Propeller
Here3 GPS
Tattu 14Ah 6s Battery

There are very noticeable oscillations in the quad when descending in Loiter and Althold Mode(attached log below)
I suspects Z vibrations are the reason
My props passby the motor mount very closely. See image below

Could this be the reason for my Z vibrations?
Also please comment on my tune. I haven’t tweaked with Loiter params yet

Log :GDrive File

It could be a good idea to space those motors up so the props have more clearance.
Vibrations are definitely a problem.
You might have to do more though, like check wiring pulled too tight or too loose, the usual…

I cant say that vibrations are the cause of instability during descent, it’s probably more general tuning.
Sometimes this instability could be caused by MOT_THST_EXPO set too high. Yours looks OK how it is now. If there’s still issues after the other work (below) you could lower it to 0.7 or even 0.6 . If you did change it you’d have to do some retuning, so leave that as a last resort.

First upgrade to latest stable firmware (4.3.2) and check these new defaults for Cube Orange

I would set these too
FENCE_ENABLE,1 ← and check the other Fence params
INS_ACCEL_FILTER,10 ← will be the new default eventually, very safe to use this
LOG_BITMASK,180222 ← reduce the logging a bit unless you really need fast attitude
And these, yours were close and these wont make much difference, but might as well

You can also try raising the accel values and see how that affects the stability

The FFT has picked up on a harmonic, 112Hz, instead of the base frequency probably around 50Hz.
I would say disable the FFT, at least for now, and enable the HNOTCH using ESC RPM data.
INS_LOG_BAT_OPT,4 ← gather both pre and post-filter data

Then I would do

  • a test flight in AltHold and Loiter, check logs for HNOTCH settings and anything else
  • run Autotune, that should sort out the instability

After the tuning and descent rate issues are sorted out, if you are going to frequently swap payloads, then I’d look at enabling the FFT again and check why it’s picking up on the wrong hover frequency.