Pls help to understand source of yaw rotation


i need help to confirm if i have now a faulty ESC - i got 2rd (rear left) motor to melt previously, for reasons unknown - very odd, so i replaced all motors on the bird. i then ran an autotune, all seems fine EXCEPT that now upon giving max speed, of just forcing drone to go above certain speed i get a consistent yaw rotation (clockwise, i think) happening. it did not do it before, ever.

while in simple mode it still maintains correct sense of the direction - so i presume compass is not really affected and yaw is not mag induced, and the log analyzer agrees - mag interference is 21% or so, not too bad.

Log File C:\Users\putki\AppData\Local\Temp\tmpCD23.tmp.log
Size (kb) 35479.8720703125
No of lines 437970
Duration 0:02:31
Vehicletype ArduCopter
Firmware Version V3.7.0-dev
Firmware Hash 389b3477
Hardware Type
Free Mem 0
Skipped Lines 0
Test: Autotune = UNKNOWN - No ATUN log data
Test: Brownout = GOOD -
Test: Compass = GOOD - mag_field interference within limits (21.78%)
Max mag field length (598.59) > recommended (550.00)

Test: Dupe Log Data = GOOD -
Test: Empty = GOOD -
Test: Event/Failsafe = GOOD -
Test: GPS = GOOD -
Test: IMU Mismatch = NA -
Test: Motor Balance = WARN - Motor channel averages = [1240, 1345, 1241, 1228]
Average motor output = 1263
Difference between min and max motor averages = 117
Test: NaNs = FAIL - Found NaN in POS.RelOriginAlt
Found NaN in CTUN.TAlt
Found NaN in CTUN.DSAlt

Test: OpticalFlow = FAIL - FAIL: no optical flow data

Test: Parameters = FAIL - ‘MAG_ENABLE’ not found
Test: PM = GOOD -
Test: Pitch/Roll = UNKNOWN - ‘BarAlt’
Test: Thrust = GOOD -
Test: VCC = UNKNOWN - No CURR log data

If anybody could find 5-10 min to take a look at this data and may be see something - i would really love to understand what causes that yaw rotation now - i had there in log a pos.hold back and forth movements and a straight up movement in stab mode - that all causes yaw rotation now.
ESC is the Holybro Tekko32 35A 4-in-1 BLHeli32 3-6s ESC, updated to latest blheli32 code,
which is a pity it is went bad on me.

i would really like to confirm that it is indeed the ESC before trying to swap it out. thx!

The flight controller is definitely struggling to control yaw.

Here, you can see an uncommanded (RC in 4 is flat) change in heading. The yaw leads the desired yaw, which means that the flight controller isn’t intending for that to happen, and in fact it is trying to fight it by giving a positive yaw rate to counteract the negative yaw change.

There may be a number of causes for this, here are my notes:

  1. Motor 2 constantly has a higher PWM than the other motors. This may indicate a mechanical issue (bad bearing or prop) or a configuration problem (ESC is not calibrated the same as others, although you’ve got a 4-in-1).
  2. Your copter is very overpowered, do you plan on putting a payload on it? It hovers at a mere 8% throttle, so the flight controller doesn’t have much to work with to control attitude. I don’t see the PWMs bottoming out very often, though, but you might want to try lowering MOT_SPIN_MIN. You may find that adding weight (bigger battery) or using smaller props may solve this.

thx. so, all in all, it sounds like a bad ESC. it is a 6" chameleon LR Ti racer model, it is overpowered as it is supposed to go, well, quite fast, and it does. not an easiest build to make… i have bigger batteries for it, but, the first thing to fix was to understand the origin of this new behavior. thx so much for your help, i will try to swap the esc.

before that previous motor 2 got melted it never had such issue. new motors are similar to what was used before, and new props are on. so, dunno what to blame here except the esc.

Just to confirm - it was indeed a damaged ESC. i replaced it and it now works fine.