Crash Report - request to resolve the cause

Cube Autopilot
1

Hello guys, can you please help me solve my latest crash?

Here is log of my flight (OneDrive): https://unihk-my.sharepoint.com/…/EUC3SPj7B5dLpEm4fs_ZNGkBx…

It is heavy lifter X8. Take off weight was 11kg (I flew without payload).

Flying with stock PIDs was acceptable, Loiter, AltHold, RTL and Auto modes worked flawlessly. Anyway with stock PIDs when I fully Rolled to one side and then centered the stick, the X8 was so fast when correnting the angle that it overshotted and got slight ressonation and then calmed itself after 2 or 3 bounce backs.

So I tried autotune with hope that it would fix the issue. After Autotune i tried it, seemed great. I landed, disarmed, armed, took off and then I was flying in Stabilize. After few moments the X8 got massive oscilattion - overcorrecting itself. I had to release parachute, because anyway it would end up in massive power crash.

Can you please help me find real reasons behind this crash?

Thank you.

Setup:

CubeBlack (Arducopter 4.0.3)

8x T-Motors U7 420kv with T-Motors 18x6,1 props
8x T-Motors FLAME 80A ESCs

32Ah 6S Battery, Mauch Power system

2

Defaults were too aggressive.
Check the tuning guide: https://ardupilot.org/copter/docs/tuning-process-instructions.html
And this spreadsheet: https://www.dropbox.com/s/8u9v3ddph6u9u3t/Initial%20parameters.xls?dl=0

I’d set these and try autotune again

These will be required, they will help a lot, especially as battery voltage changes:
MOT_BAT_VOLT_MAX,25.2
MOT_BAT_VOLT_MIN,19.8
MOT_THST_EXPO,0.73 - if your ESCs “linearize” thrust then you could go as low as 0.2

This will smooth out your RC input:
ATC_INPUT_TC,0.22

These are calculated from your flights, and best to set them:
ATC_THR_MIX_MAN,0.5
PSC_ACCZ_I,0.57474
PSC_ACCZ_P,0.28737

Your bat settings were OK, these are more standard:
BATT_ARM_VOLT,22.1
BATT_CRT_VOLT,21
BATT_LOW_VOLT,21.6

From the spreadsheet and your vibrations, I’d recommend these:
ATC_RAT_PIT_FLTD,13
ATC_RAT_PIT_FLTT,13
ATC_RAT_RLL_FLTD,13
ATC_RAT_RLL_FLTT,13
ATC_RAT_YAW_FLTE,2
ATC_RAT_YAW_FLTT,13
INS_ACCEL_FILTER,18
INS_GYRO_FILTER,18

Personally I’d change those Autotune PIDs too, something more conservative on D term to start with:
ATC_RAT_RLL_D,0.005
ATC_RAT_PIT_D,0.005
And increase these a little:
ATC_RAT_RLL_P,0.11
ATC_RAT_RLL_I,0.11
ATC_RAT_PIT_P,0.11
ATC_RAT_PIT_I,0.11
I’m not saying Autotune would be wrong or a bad thing, but it might have been working with bad information to start with. Once you’ve got this aircraft going OK without all the overshoot, then run Autotune again, even a couple of times. And investigate the Harmonic Notch filter.