Yaw Is Unstable/Oscillation

Been having an issue with a custom quadcopter build, with the yaw oscillating in particular. The quadcopter is a large build made of square aluminum tubes in an “I” configuration but the engines are placed 2m apart from each other, square. I’m using T-Motor U13Ⅱ KV130, T-Motor FLAME 180A HV ESC and 26x12in, motor,esc,prop combination and a 14s lipo battery.

This a reading from my logs showing desired and current yaw which is very unstable:

and the pwm values for the engines which appears that the cw and ccw pairs are working against each other:

I have tried autotune before but it never finished, I read the messages tab on mission planner and it keeps trying the first process of tuning. I used the initial parameter plugin on mission planner and then after lowering the value for ATC_ANG_YAW_P from 4.5 to 3 and increasing ATC_RAT_YAW_FLTT from 10 to 30 the quadcopter takes off much more stable but tends to yaw when I increase or decrease throttle.

Attached are my log files.

Appreciate any help given.

Yaw is just a visible symptom, it will sort itself out once Pitch and Roll are sorted

There is definitely some frame-twist or motor mount issues, with motors 3 and 4 having to work harder to counteract some physical yaw bias with motors 1 and 2.

Set up the Harmonic Notch filter too, these should be a good starting point:
INS_HNTCH_ENABLE,1 ← set this then refresh params to see the rest

You could also try a higher MOT_THST_EXPO of 0.4 to see if that improves stability.

You’ll have to run Autotune once you get these things sorted. Feel free to supply more .bin logs as you progress.

1 Like

Hi there @xfacta ,

Thanks for the advice, I’ve started with the Harmonic Notch filter as you suggested and did a test flight. Attached is the link to the bin file: 2022-05-03 12-15-22.bin


I’ll attach some cameras on the arms and do another test, see if there is any noticeable frame or motor mount twist.

@xfacta , I mounted gopros and did a flight to see any flexing, nothing of concern was noticed, just inital vibrations when taking off. By the time it was in the air, it was ok.