Misterious crash, we have the log, but no clue what was wrong

ArduCopter Copter 3.6
1

Hi Everyone!

One of my friend has a huge spraying drone, and he had a crash last week. Since than we are trying to understand what happened, but we are lost. If you could help, it would mean a lot for us, so we could spare the expenses of a similar crash.
First my friend was doing an auto spraying, when suddenly the drone stopped in mission, and started to waggle, and since it was far away at that point, we are not really sure what happened, but according to my friend, he tried to change the flight mode to ALTHOLD, but the drone was not repsonding to the climb command, instead it landed safely. The log of this fligh is also in the folder below. The crash came later.
After recovering the drone from the middle of the field, it finished 2 auto mission without any problem, but in the third it crashed. I can see in the logs that the battery died, but it seems to me that the drone was acting weird before the fall in voltage. We tried to understand what happened, but we are not professionals, so It would help us a lot If the wonderful community could clear the issue.

Thanks in advance:
Karlo

2

Could have been desync of motor 8

image
image1330×338 148 KB

Voltage also drops very low right at the end, so it could even have been an electrical short or ESC/motor failure.
Current monitoring is not working, that might have been useful.

3

Thanks a lot, I also noticed this, but Im not sure what could have caused it. We will test it, and see what we can find out.