Quadcopter goes into severe oscillations immediately after takeoff

1

Hey everyone,
I am working on a quadcopter but can’t get it to takeoff and stay stable in the air. The motors are each spaced uniformly about 36 cm from the CG and the drone weighs roughly 8 kg. We have conducted three tests so far all with the same results. I’ve attached a video of the first test and it’s flight logs access link below:

Cursh T1

At this point we thought the issue was that our motor mounts twisted on the boom causing the thrust direction to change and the drone to spiral out of control, so we tightened the motor mounts, making it extremely difficult for them to twist about the boom. We also introduced a vibration dampening mount for our flight controller inside the chassis of our drone. The results of our second test were unfortunately the exact same thing.

Crush T2

For the third test we added extra shielding to our ESC signal wires, and we had the same result.

Crush T3

We are using the basic tuning guide that comes with the PX4 Quadcopter airframe. I’ve seen some recommendations to decrease the rate controller, but I honestly don’t know what the issue could be and why it’s so consistent.

Would appreciate any help on this, thanks!

2

After reviewing your log, I recommend lowering the attitude controller gain, such as MC_PITCH_P and MC_ROLL_P, from 6.5 to 3–3.5. The rate controller should be set to 0.11 and re-tuned once it can hover.

Flight tests with improperly set rate/attitude controller gains in the POSITION HOLD mode can result in cataphotic accidents. You should attempt Stabilize mode.

Also, enable Highrate in SDLOG_MODE to see the entire range of accelerometers/gyros and use it to adjust the cutoff frequency and notch filter. It also contributes significantly to flight performance.

Reduce the tilt angles MPC_MAN_TILT_MAX and MPC_TILTMAX_AIR to 25-35 degrees to limit acceleration/speed during the test as needed.

Please carefully study and follow the guidelines in Multicopter PID Tuning Guide (Manual/Advanced) | PX4 Guide (main).
and
Tests Flights | PX4 Guide (main)

I hope everything gets better soon.

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