I’m new to these forums so I apologize if this is in the wrong place or has inadequate information. I will do my best to explain my problem completely but if I am missing something please let me know.
This is the build I currently have:
- Tarot T960 frame
- Pixhawk 3 Pro flight controller
- Drotek F9P RTK GPS + compass linked here
- Hobbywing 40A ESCs
- Tarot 5008 340 KV motors
- 1855 props
- X8R radio
- 915 MHz telemetry radio
I have been trying to test this out by doing position hold hover tests for the past few weeks. It started out with serious vibrations or instability in the roll and pitch axes (see video here and log here). I figured it was probably propeller balance since we had not flown this copter in over a year. So I spent some time balancing the props and adding a vibration mount to the FC. Here is a video of another attempt where it ended up flipping over. Here is the log for the same flight:
NOTE: between these two attempts I also had to roll back on the PX4 firmware revision. I was using v1.11.1 the first time and found that after mag calibration one of the three magnetometers was not being detected (2 on FC + 1 on GPS). This was not an issue on v1.10.xx revisions. I managed to reproduce this issue on another FC + GPS so there is clearly a bug in the code somewhere.
We tried again today several times. Position hold tests showed the same type of behavior; small instabilities in the roll and pitch axes that seem to amplify over time. We tried Altitude mode and that just ended up flipping the drone over. We also tried changing the derivative gain a bit but that didn’t seem to do much either. Here are the logs from earlier today:
NOTE: One important thing to note is that in all these tests I see the same type of behavior on the graphs: there is a lot of vibration (“Raw Acceleration” and “Vibration Metrics”) and the “Pitch Angular Rate” and “Roll Angular Rate” show an amplifying sinusoidal shape. “Raw Angular Speed (Gyroscope)” also show similar waveforms in each instance in X and Y. Typically this would indicate a mechanical issue by my understanding but we’ve flown this copter before albeit using a Navio2 and Ardupilot. I have also tested each arm independently in the powertrain by measuring its thrust on a weighing scale. I honestly can’t think of what else could be going wrong. Can someone please help? Could it possibly be the flight controller? Perhaps FMUv4 does not work well with hexacopters? I have tested these avionics on a quad and it works perfectly fine.