Rapid attitude change midflight

We recently faced an issue on one of our drone whereby it started very rapid oscillation midflight in Auto mode.
The pilot was able to save it somehow and land successfully. But the drone could have very easily crashed. I am not able to figure out the reason for such sudden changes.

We had a smooth flight just before this one. Not sure what happened in this flight.


Autopilot: Cube Orange

Firmware: 4.1.5

Motor: T motor MN3110 700 kv with 12X4.5 APC propeller

ESC: Tarot 20 Amps

log file:

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Update to ArduCopter 4.2.3 and check your MOT_THST_EXPO parameter.

is something mechanically loose?

where is the CG? the front motors are almost not doing anything at times

or some kinda of forward movement resonance? something catching the wind while moving forward?

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Hello Michael,

Thank you for your comment.
Nothing is loose as such. However, the payload is on a dampener mounted on a single CF sheet. Can that lead to such vibrations?
Enclosed are the image of the payload mounting
IMU 0 and 1 are completely dampened. Is Vibe on IMU 2 a cause of concern?

Regarding CG: It’s also fixed as well. I am using a custom-built Y Frame type. Where should the CG be in that case?
I’ll share the log of the previous flight whereby I am not seeing such a drastically low RCOU1. Following is the link.

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