Unstable hover - large craft

🧪 Flight Testing & Log Analysis
1

Hi All,

I’m currently in the process of moving one of my large craft (30in props) over from arducopter onto PX4.

(Pixhawk Cube, TMotor Alpha 60a ESCs, 12S battery, 30in Props)

June 8th

I have spent a couple of days tuning the craft’s PIDs from the stable ones I had in Arducopter as a starting point but still notice oscillations during hover and regular flying.

I am new to PX4 it’s IMU filtering options and am wondering if this could be a vibration issue as well as an issue with the PIDs that I am currently using?

I have been changing the following along with PIDs:

IMU_GRUO_CUTOFF
IMU_DGYRO_CUTOFF
IMU_GYRO_NF_FREQ
IMU_GRYO_NF_BW

This craft flew stable in arducopter when the proper vibration filtering was set so I am almost positive there is not an issue with the craft itself.

If someone could take a look at a log and help point me in the correct direction that would be greatly appreciated!

3

Hi! I am tuning a very similar platform to yours. What IMU_gyro_cutoff and Dgyro_cutoff parameters have you set on px4? do you care to share your relevant parameters? Thanks!

4

Hello,

From the log @Devin_Host shared, looks like they’re 55Hz and 30Hz respectively for gyro_cutoff and dgyro_cutoff

5

Hello @Devin_Host,

I don’t know if you are still troubleshooting your problem, but I notice a large peaks around 40Hz and 60Hz in your log under Actuator Controls FFT. I think something may have been loose on your airframe causing a low frequency vibration.

Typically you would want something lower for your IMU_GYRO_CUTOFF and IMU_DGYRO_CUTOFF for a bigger airframe like yours.