Log Analysis - Sudden persistent spike in y-vibrations leads to crash

[hy-user]

Hello,

Requesting help again on another strange crash event. Running Cube with Copter v3.6.9. The vehicle went down shortly after takeoff. Log;

U011_1565103260.bin (1.9 MB)

The vibration graph is unique, I have never seen anything quite like this before:

Midway through the flight, there is a sudden spike in y-vibrations with basically no change to x or z vibrations (which is strange in itself). Even stranger, the y-vibrations persist at the same level for some time until the vehicle finally crashes. What could cause such a spike and keep it there? Because the rangefinder altitude stays constant and there are no x/z spikes, I am fairly certain that the vehicle did not hit anything.

The Gyro P rates also go haywire at the same time:

I am not sure what condition (if any) can cause such clean y-axis failure. Is this a possible bug or IMU fault?

Thank you for the assistance.

[mboland (Mike Boland)]

Firstly to clear up that X and Y suddenly increase.
Looking at IMU data

There is also a bit of contraction in the Z axis frequency as well but no real increase amplitude.
It’s more curious that the VIBES shows only the Y increase you observed.

It looks very much like a motor/frame failure looking at the RCout.
There is a definite event where motors peaking and dropping.

As you don’t have a lot of headroom, avg 1700 output, that seems to have contributed.