F330 vibration problem

Hi all,

We have a DJI 330 Frame, with e-flite 370 1200kv motors, 8x4.5 props, 20amp esc’s, 2200 3s lipo, and holybro pixhawk 4, running the 1.10v of px4.
We have added an extension to the frame, to mount the companion computer and the PDB (as you can in the picture). Total weight is 950 [gr].

For testing, we connected the quad to a steel frame with elastic bands to stop it from flipping and crashing.

Until we reach hover thrust everything looks fine, but when increasing the throttle slightly more, the drone starts to shake badly. When reaching 75% throttle, the shaking stops and it looks normal again.

At first, we tried testing without the bands and the steel frame, and the drone flipped at the hover thrust, and we broke 2 props.

Attached logged data from the flight controller:
Logged Data

Video from the test:
Testing video

We are not sure if the vibrations are caused by a structure issue or a wrong PID or filters configurations.

Your thoughts are appreciated.

Thanks in advance,
Iftach.

In the spectral density chart you can see each of the 4 propellers speeds very clearly so balancing them would help. You’re flight controller looks elevated from the frame which amplifies the vibrations.

As far as parameters you’re p rate and d rate gains are probably too high but for smaller multicopters that are capable of rotating quickly the delay generated by the default low pass filter values.

You have harmonic coupling issues with that test stand so what I do to start is to tie a string around my drone, give it a little throttle, and pick it up. It would probably be safer to put the string over a pulley so your hand isn’t above the drone. Start with low gains and bring them up until the vehicle seems flyable. Once you actually fly it the PID analyzer is pretty good at telling you what to do.

Hi ericleal,

As you suggested, we lower the P and D rate values, and It solved the vibrations problem completely.
We are now able to fly it without any issues.

Attach is the logged data from the last flight:
Logged data from flight

We will appreciate if you can take a look and see if there is anything else we can adjust to improve the performance.

Thanks alot,
Iftach.

The level of vibration you are seeing is still high at the motor rotational frequency. You can find a lot of videos online about propeller balancing which would help. The p angle gains look too low which can cause integrator windup and problems with the velocity mode controller.

Hello again,
Thanks for the help. We will to balance the propellers and increase the p angle gains.