Crash Analysis

This morning my quad crashed near the end of a mission. I’m not sure why the crash occurred but it appears to be power-related. However my 3.6A battery was at 27%, according to Mission Planner, and when I recharged it it was full after 2.4A, so this appears to be correct. The individual cell voltages were all around 3.77V after the crash, and the battery is a 30C, so it doesn’t seem like the quad could have tried to pull more amps that it could handle.

Would appreciate any feedback (log attached). The trouble starts at about line 93.6K, when Roll and DesRoll start to deviate. ThrOut quickly rises, but Curr is unable to cope. Vibrations also max out after this, but this as a result of the throttle rising, not a cause of the crash. It clearly happens only after the throttle maxes out.

I had to zip the log because it was over the allowed 5MB.

Unfortunately, no motor logging hinders analysis of this one a bit. Given the very sudden divergence of roll and pitch, I think you had a power plant failure, probably right-rear motor.

Hi Jonathon, and thanks for the reply.

Great insights, I have to agree with you. I have spent the last hour simulated the pitching of the quad at the time of the incident and it does appear as if the right rear motor loses power. The initial roll is a small blip indicating that the right rear loses power, the more violent pitching thereafter is the attempt by the flight controller to stabilize, each time overcompensating. But none of the pitching suggests that the right rear was contributing.

I tested each motor/ESC combination after the crash and they all work, but at the crash site the right rear prop was not on the motor and the spinner was about 2m away. This suggests that it was a lose spinner that caused the issue, although we can’t be 100% certain.

If it was a spinner its unfortunate - I had decided to move towards bolt-on props and I was only using these because they were my remaining carbon props. I hadn’t tested the tightness of the spinners for about an hour of airtime, which shows what can happen when you overlook a small thing.

I am rebuilding the quad - everything appears to be OK except for the props, and parts of the frame. Fortunately the electronics seem to all be OK. I will enable motor logging when its flying again and do some low altitude testing over bushes.

Thanks again.

Loose props are a pretty common cause of issues. If you get an X8 they won’t cause an issue as long as you give yourself safety margin (hover @ ~65-70% max) and get your motor order correct.