X copter with oscillation around its diagonal

[Maeldd (Mael Donnard)]

Hello,
We have a drone that was really stable for several flight and lately start oscillating on a diagonal with a mix of pitch and roll oscillation.
For exemple for the first flight we had oscillation on the two CCW motors and nothing on the CW motors and it switched for the second flight.
Some quick info about the drone

• 170kV motors
• 12S
• 22 inch props
• Diag about 1m
• 8kg for the tests

Log :

log_130_2024-3-21-11-19-18.bin

log_131_2024-3-21-11-22-52.bin

log_132_2024-3-21-11-25-02.bin

If you have any idea.

Thanks for you help !

[Maeldd (Mael Donnard)]

I keep digging.
Oscillations seems to be auto-amplifided. I suspect an issue with vibration but not an expert.

The drone flew for about 10 hours before having this issue so I suspect a mechanical reason.
What are yours thought about it ?

Thank you !

[amilcarlucas]

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[Maeldd (Mael Donnard)]

Oh yes it would be great ! Thanks @amilcarlucas for the invitation.

[Maeldd (Mael Donnard)]

Still investigating my issue.
Reducing the MOT_THST_EXPO has clearly an impact the drone behavior and its “capability” to start these oscillations. (ESC T-MOTOR 60 A 12S)
For now I have

MOT_THST_EXPO = 0.2
MOT_PWM_MIN = 1100

There you can find some videos of this behavior :
IMG_2369.MOV - Google Drive (good flight)
IMG_2370.MOV - Google Drive (oscillation)

[Maeldd (Mael Donnard)]

Is it possible that these oscillations are happening because the motors are hitting the MOT_PWM_MIN when pushing the control “too far”?
Increasing throttle during oscillations seems to stop it.

The drone could be “too light” ?

On these logs, the oscillation is added to the second part.

[MindProbe]

Check this out

Using "measured" MOT_THST_EXPO: What improvement can one expect?

Hi Olli, I think I completly agree with you here. I gave those two example because they are obvious symptoms that your MOT_THST_EXPO is a long way from correct and that it should be checked before moving forward. For most aircraft and pilots they do not operate over such a broad range. It is worth keeping in mind here that ArduCopter has been designed to operate over a very broad range of aircraft and applications. As such we must me more comprehensive in our approach. This also means that man…

[Maeldd (Mael Donnard)]

thanks @MindProbe.
I did read this thread.
I doesn’t seems to be the issue because we did test the combo motor/props/ESC on a test bench last week and the 0.4-0.3 seems correct like many people suggest for T motor Flame ESC.

[Maeldd (Mael Donnard)]

[correction] 0.4-0.3 is incorrect, the P60-X Combo Pack X-Agricultural Type (Integrated Propulsion System）UAV Motor 170KV seems to have a linear correction for the ESC