Alt Hold/Pos Hold jerk

Hey guys,


Unfortunately i was not able to tune a copter as it has some jerking when switching from stab to alt hold/pos hold. Slight pulsing 10cm jumps and jerk while holding alt. i have never experienced this before. Thr_mid is set correctly at 25%, did an autotune reset parameters etc. it is not locked in as with my other copters. FCU is damped, props are balanced. Did play arround with the ins_ filter (15-20 hz) settings but did not help except in the logs. Any idea what else could be the reason?


Looking at the IMU data it seems you have a lot of vibration, especially in the Z axis, and in my experience this has always caused large divergences in any mode using auto altitude hold.

Thanks for having a look into it! So that’s bad news for me right and rebuilding the frame is my only option so far? Strange i could not see the vibration as such when checking the log. I do youse ac3.3.3 so i thought the vibes seem fine. Any other suggestions to get it to fly decent?

How have you mounted your FC?
I use a suspension method that seems to cope well with noisy frames.

I did mount the FCU onto this 3D printed mount. Today i retuned the props and motor bells (normally motor bell balancing has little to no influence until now). Will try with this setup again. I’m using really low RPM as my hover is at 25% with 490kv motors and 4s bat 17x55 cf props. If testing i might as well tune down the pid and play again with the filter settings (5-10hz maybe there is a connection to the low rpm). I was actually holding the quad and “feeling” the vibration and they are really as close to not existend in stab once i switch over there is some kind of jerky behave again :confused:
would a short video help?
thank you for your assistance so far!

@rmackay9 could you please have a “quick” look at the log. i already did my research and i guess it could be related to overpowered copter. I guess i have to adjust following parameters:
ACCEL_Z_P (lower to ~0.3)
ACCEL_Z_D (up to ~0.01)
ACCEL_Z_FILT_HZ (cut to ~10hz)
Unfortunately i was not able to find enough information in the documentation to feel confident doing these changes could you guide me which parameter to change in what order? As stated above i run very low rpm on the motors (490kv 4s).

This is how I have had great success with vibration dampening and use it on all craft now.
The silicone balls in the 2 piece dampeners I found too stiff (even the softest balls)

Silicone ‘O’ Rings - normal ones and rubber bands degrade.
1mm Carbon fibre base.
Sorbathane layer
1mm Lead sheet
Futaba Gyro foam d/s tape

Of all the combinations of material these have given the best and most consistent results.

thats actually a nice design @mboland i can see you got some rubber bands stretched to a cf plate and on top there is moon gel another cf and a sponge? :smiley:

thats like multi layer isolation for multiple frequency. i guess my damping is not as good but i also did accieve good results with it. you should try and compare. print the plates and use these balls:

they have a “Safe Load Weight: 35g/ball”