Pixracer r14 wobbles/shakes, hot motors, jumping rpms motors 1 & 2

ArduCopter Copter 4.0
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1

Hello everybody,

I have been using the forum for inspiration & guide in order to build my first quadcopter running with FC Pixracer.

Problem description
I had finally 2 succesful flights, but after one bad crash (fail GCS connection may be) it started to wobble severely because of motor 1 & 2 fluctuating rpms. The two motors become quite hot, way hotter than motors 3 & 4.
After the crash, the quadcopter had just a scratch on motor 2, but the ESC looked intact and the motor turns without issues. Also a slghtly broken frame on one angle, but it’s minor.
I reflashed the firmware (4.0.6), resetup everything, did allcalibrations and the wobble even got more severe after the 3rd flight after the crash(at the begginning it was only in stablize mode, but then was disappearing with loiter and autohold). The wobble is on every mode now, flies, but very shaky.
I tried to swap the motors 2 & 4 (paying attention to rotation during setup) and the motor 2 looked underpowered and the quad was leaning towards it and looked as it would turn around. Therefore concluded that’s the ESC. I had only simonk for the test, while the others esc are blheli_s and may be my test was not good because of this. Anyway, the quad flied, but after 1-2 mins crashed, surely because of the simonk odd esc.

My analyze: I reviewed the log and I can see this clearly in RCOUT. I don’t see any very large fluctuations of the gyro, acc & compass sensors.
The problem is, I cannot find the exact reason for this.
Can somebody help me please how to analyze and fix the problem?
I attach the last logs with the apparent wobble.

Logs
https://drive.google.com/drive/folders/10eukdDms0xWpcysgeXr3rlC9AdOHFJuU?usp=sharing

Setup:

  • Pixracer r14
  • 260mm X foldable frame
  • Props 6040 (pass very close to the frame, but don’t touch it)
  • PDB Matek
  • 4 ESC Racerstar 20a blheli_s
  • Motors Emax MT1806 2280kv
  • 3s battery 4000mah
  • Total weight 700g (with battery)
  • Thrust to weight ration around 2.5

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Thanks!

Kris

2

You haven’t followed any of the Initial Tuning Process Instructions. All your filters are wrong for this size craft.
https://ardupilot.org/copter/docs/tuning-process-instructions.html

Connect to Mission Planner, Hit Alt>A for the tuning plug-in, enter the values as prompted and manually change the parameters shown.

And the motors are MT1806 not 1608?

3

Be worth it to get a new set then. I set mine up as 32 bit dshot and then reduce the PID’s… BTW I think you can drop the GPS as well.

4

Thank you very much! I totally forgot to follow the initial tuning process after the crash, just reflashed directly. I tested the quadcopter, it was very stable for the first quick test in stabilize mode. I used the old esc, no problem.
@Quadzilla I tried to flash dshot, but my esc Racerstar 20a accept only oneshot & normal. I’m currently with oneshot. Why do you say that the GPS is to drop? I tried quickly loiter mode, it holds very well position(Neo M8N GPS). I purchased spare esc just in case, same type for budget reasons.
Thank both for the quick reply, I really apreciate it. Please don’t hesitate to share your opinion if you think I can optimize/modify/upgrade some parts, I’ll be grateful!

5

Chances are you can flash firmware to those BLHeli_S ESC’s to enable Dshot. I have done so on one quad with some older Spedix ESC’s. If you want to give it a try start here or Google Jazzmavrick.

Beyond that there is Bidirectional Dshot coming to Ardupilot. It’s in Master for a few boards now. Like Betaflight this sends RPM data back on the ESC signal line at ESC update rate and can be used as reference for the dynamic notch filter. But in the meantime you can use the dynamic notch filter anywy with a throttle reference. Read the Wiki about it