High vibrations during fixed position (without props) tests

hello every one,

I made some test with my drone (quadro copter (self constructed), X configuration, 800 mm using Pixhawk 4, ESC’s - Dshot600) to determine the reason for high vibrations.

The drone was tested without props lying on a table (fixed position scenario)
At first I wrote a python program using mavsdk to drive the motors using the motor_test command.
The motors was tested from 1 to 100% and the motors together with the frame create very small vibrations.
The flight controller is bypassed in this scenario. This tests shows that normal motor rotations create no vobration.

The next step was to drive the motors using the remote control (FrSky HorusX10S).
I use the manual flight mode. In many tests (not all) after arming, the motors running with the minimal rotation and without vibration.
Then I gave a small amount of thrust (about 3 - 6%) moving the throttle relative slowly and the drone began vibrating very strong.
With the logfile analysis I could see that output which goes to the motors create an oszillation between 200 and 1000 rpm with 2Hz.

In this situation I have some questions:

  • Are the tests valid ( (fixed position scenario ) or create the fact that the drone could not react in a normal (flying) way additional problems which the flight controller can not handling correctly ?

  • Could this vibrations related to PID misconfiguration ( I choose the standad settings) ?

  • Do I have to modify some Parameters to allow meaningful fixed position tests ?

Best regards
Andreas

I would check that the motors are correctly aligned and the props are not out of balanced.
Testing with out props for vibration really does not mean much.

Many ours later I could anwser my question:

“Are tests valid (fixed positionscanario)…”

Yes, you can test the corrrect working between Flight Controller, ESC and motor in a fixed position scenario - the copter laying down on a table without mounted props!
The problem with the oszillation between 200 and 1000 rpm with 2Hz was not related to PID misconfiguration and not related to parameters.
The problem was that the DShot - Mode of the ESC is not working correctly if the flight controller
control the ESC. The ESC in DShot - Mode was working fine with the motor if the ESC was driven by the motor - test utility.
I have used the documentation which describe the wiring for this use case and the parameter setting.
I think that the firmware has some errors related to the use of the DShot - Mode!
After switching over to normal, old PWM Mode the setting was working!

Best regards

Andreas

Hope this helps…Last time I faced a vibrations issue was when my Roll-rate PID gains were different from Pitch-rate PID gains. (Not sure though, because you said you used standard settings…)

EDIT : Oops. Missed your reply earlier. glad to know your problem was solved.

I think the problems have something to do with the mechanical design of our drone.
Now I have built a Tarot X4 drone using the same flight controller, ESC’s and motors and the same PID parameter settings. The Tarot X4 drone has the same size and weight.
The Tarot X4 drone is currently not flying optimal (I think PID tuning is necessary) but significantly better as our drone.