Hexacopter Flip - Logging stops midair

Flight Testing & Log Analysis v1.12
1

Hey all,

I am having a hard time getting my (big) hexacopter to fly. My tests:

  1. First test flight with v1.12.3 after a fresh setup and calibration. The first flight was fine, I flew it manually and the drone was sitting perfectly in the air. I was able to fly an 8 without any issues in Hold.

Log: https://logs.px4.io/plot_app?log=c745caf5-db7a-4838-aa96-11e731279f8c

  1. After this initial test I wanted to do some small auto mission. After manual takeoff I switched into Hold and after only a few seconds of static hovering in the air the drone was flipping over without any input from my side.

Log: https://logs.px4.io/plot_app?log=378af897-8d1e-4ffc-908d-110190ff256c

The fishy thing here to me is that logging stopped midair, so the crash is not visible in the logs.

  1. We rebuilt the drone because it got severely damaged. New Pixhawk, new GNSS Antenna, new Battery. We flashed to v1.13.3 and gave it another shot. We basically experienced the same as in 2), but worse. Just a few seconds after takeoff the drone was flipping over. This time I’d say it was oscillating quite a bit early and I tried to counter it with stick inputs but the flip was inevitable. I was not even able to switch to hold.

Log: https://logs.px4.io/plot_app?log=3c70d53c-f568-4685-8469-8026af8b4ea7

Fishy again: The log did not cover the full crash even though the drone was still on after the crash. In this log I’d say there is a lot of noise on both the accelerometer and the noise detection. It was flying like shit this time, so it is not surprising.

All in all I’d say there is some hardware failure in there somewhere, what do you think? Especially, which component could it be? The “logging stopped midair” seems to me like the biggest red flag in the logs. And this seems to happen only in two cases, power out or failure of the autopilot. The latter I’d more or less rule out. So something shorting / rebooting the autopilot?

Thanks for your suggestions and best regards,

Alex

2

After disassembling the whole thing I noticed the drone is powered through the BEC of an ESC. I remember this was done in the old days, but this looks to me like a perfectly legit cause for a power out. The ESCs sit directly next to the motors, so I’d wager it highly unlikely they provide perfect 5V. And after reading in the cube docs it appears that at 5.7V the pixhawk may power off to prevent damage. So in case of high ESC burst the BEC may simply kill the pixhawk which would explain the logs stopping and the drone flipping. What do you think?

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