I’ve acquired a multicopter from Foxtech and have been trying to put it to work this last few months without success. The frame I’m using has the following characteristics:
- Frame: Foxtech D130 X8 (https://www.foxtechfpv.com/d130-x8-v2-frame-p-1293.html)
- Motors: T-motor U8 kv100
- Power Supply: 12S
- Autopilot: Pixhawk 2.1 (cube)
- Firmware: Ardupilot v3.5.5 (hash 27229c83)
- Propellers: Carbon Fiber 2885 (https://www.foxtechfpv.com/2885-carbon-fiber-propeller-cw-ccw.html)
- Weight: 13 Kg
Last week I performed some flights which ended with a crash. On the first flight the multicopter performed takeoff in AltHold mode and, once it reached a safe altitude, I changed it to Position mode. At this point I noticed the first odd thing with the multicopter starting to oscillate severely. As a corrective measure I changed the mode to Stabilize and the copter climbed 10m to 20m above ground. This resulted from the fact that the RC channel for the throttle was in the mid position (to have 0 vertical velocity) and then, when the mode was changed, this value was used as a thrust reference instead of a vertical velocity. Then, I safely landed the copter.
With this type of response I have identified that clearly something was wrong with the position control, so I performed a second flight only in Stabilized mode to assess if the attitude control was well tuned. On this second flight, once the copter was in hover position it started to show some oscillation. I also noticed that the attitude response was sluggish. Hence, I started to lower the copter altitude to land it. Almost instantly as I reduced the throttle the oscillations started again and as I reduced the throttle they worsen until the point the copter performed a flip and crashed into the ground.
After reviewing the flight logs I saw that the rate control wasn’t as sharp as I would think, but at this point I can’t find the origin of this effect. Regarding the sensors vibrations, everything looked well behaved and well within the values recommended (below 20dB)
As someone worked with this platform before? Which gains should I use?
Should I look in depth some component of the airframe to ensure it is performing as should be?
The log/bin files can be downloaded from the following links:
1st Flight: https://www.dropbox.com/s/ltz8njlaj2cdebz/1st_Flight.bin?dl=0
2nd Flight (Crash): https://www.dropbox.com/s/c1rj9d7wnqrj7yt/2nd_Flight_CRASH.bin?dl=0
Thank you for your help in advance and I hope we figure this one out.