Copter not holding alt in GUIDED and AUTO modes

ArduCopter Copter 3.6
1

I suspect this may be a bug.

I have a simple build with MATEK F405 WING and BEITIAN BN 880. No additional sensors. AC3.6.7

I noticed that as soon as copter starts moving it keeps gaining altitude until it reaches the destination or a WP, then it descends back down to the ALT of the destination / WP.

Example in attached log:

my base elevation is 42 m. Guided (and mission) alts are relative - 100m .

POS,305994941,42.52309,-71.1865475,179.11000061035156,100.79630279541016,101.32630157470703
...
--requesting new position at 100m
GUID,306027357,1,425226176,-711864576,10000,0,0,0
...
--starts moving:
POS,306094937,42.52309,-71.1865475,179.08999633789062,100.77618408203125,101.30618286132812
...
--now copter transitions to the requested destination - already 9m above target:
POS,317794932,42.5226417,-71.1864785,187.6599884033203,109.34822845458984,109.87822723388672
...
--reached the dest at 20m above requested alt
POS,322394929,42.5226202,-71.1864528,197.51998901367188,119.20286560058594,119.73286437988281
..
--starts descent and reaches the original atl:
POS,336394951,42.5226178,-71.1864569,179.97999572753906,101.66571044921875,102.19570922851562

when i run similar experiment with pixhawk cube and here2 everything is fine - no altitude gain

log: https://drive.google.com/open?id=1z5aXnmS6LRZ5ZAh45S7qXNEOMqDy48kQ

2

gaining altitude is often a sign of too much Z vibration. Take a look at those values.

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3

Your Z-vibes are peaking at ~90 with clipping. No reason to think it’s a bug. The Cube IMU is vibe isolated, can’t make a comparison to that.

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4

ok, thx, fc is softmounted.

bug or not a bug question: FC can certainly see the ALT delta, what else is needed to correct it.

5

You need to look at the FC mounting, might be too soft or not soft enough or resonating at wrong frequency. Also check rest of craft mechanically for sources of vibration - chipped props, poorly balanced props or other mechanical issues that would introduce vibration.

6

My guess is you nee a more compliant mount. What are you using now?

7

thanks i’m using 1cm thick double-sided sticky foam - kind of soft - it actually comes in pixhawk cube package - i reused it for matek.
I wonder what others are doing on matek wing

8

Put some small weight on the matek, it should add enough inertia to reduce vibrations.
Make sure though that it does not fall-off.

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