Noob: need help to analyze flip & crash

Greetings all,
Sorry to bother you, but I need a bit of help to analyze my (latest) crash.
It’s not my first crash, but usually I have a good idea of what went wrong, and I’ve been able to confirm this by log analysis.

However, this one I’m not sure about. I guess I’m still too much of a noob.
After a number of successful flights and a successful autotune, the copter today suddenly flipped and went into the ground during a turn and acceleration while flying FPV.
I admit that it was the first flight after I updated to latest release last night, but I don’t think that caused the failure - more likely something I did wrong.

Did I bring it into a too aggressive manure when a powerful gust of wind tipped it over?
Did I reduce throttle too much?
It could be anything and I don’t know what to conclude from the log.

(Thankfully, the landing was in deep, soft grass and soil. Damage was surprisingly limited)

Is anyone able to point me in the right direction?

Since you’re running 3.1.3, it is obviously not my favorite bug.

At the same time, roll diverged positive, pitch diverged negative. That’s right and forward. Front right motor failure.
Possible causes from the prop inwards:
Prop broke in flight
Prop came loose in flight
Motor failed
Motor connection came loose in flight
ESC sync failure
ESC power connection came loose in flight
ESC signal connection came loose in flight
APM hardware failure (extremely unlikely)
APM software failure (extremely unlikely)

Thank you very much for your work, jschall.

I was unable to separate the cause from the effect by myself.

I don’t think the prop itself is the cause.
Even after the crash it is still intact and bolted down as tight as I dare.

I do have bullet connectors between ESC and motors (I know- I ask for trouble).
Also, the servo-to-motor mount plate is in two pieces and the motor is free in its wires:
Broken off motor could be the cause - or it could have happened during impact (no marks or scratches on prop or copter indicating a free rotating motor)
In any case: I’m gonna remove the connectors ASAP.

An error in APM?
I’m not gonna go down that road…

That pretty much leaves a motor failure or ESC sync failure. (I would have preferred a broken prop to be the cause.)

  • I’m gonna strip the motor and do a close inspection and test in a week when I return from work trip.
    But I’m not sure how to look for an ESC Sync failure though.
    I have never had any hint of trouble on the bench…

I have not seen too many complain about MultiStar 30A Opto running a DT750 with 11x4,7 SF props.
Maybe I just didn’t look in the right place…
Does anyone have any comments in this regard?

I expect to tear everything apart in a week. I’ll post an update if I learn anything new.

Again, thank you for your time and work, jschall.
I really appreciate it!

Oh, the other option is THR_MIN too low. You’ve lowered it, so I think this one is likely.

Well, well, well

Circumstances forced the copter to stay put until yesterday, but I finally got to take it so much apart that I could replace the few broken parts and make it airworthy again.

This repair has also revealed the failure causing the crash, and as you suspected, Jschall, it was a motor failure.
One of the tree “somewhat stiff” wires from the DT750 was broken.
Using the strongest magnification I have (x35) it seems to be caused by metal fatigue.
Probably due to the combination of stiff wire, vibration and motion from yaw servos (This particular build had yaw servos on all 3 motors (I know - I just wanted to try it))

This also reveal one of the not-so-good things about the DT750; The wires on it are not the best and most flexible ones.
I guess I should have known that this might happen. I did strengthen all the wires from the motor using Epoxy, but I should have gone the extra mile and replaced as much as possible of it with better wires.

Just need to do some aerial photography the next couple of days - Then I’m gonna take it apart and move it to a quad-frame.

Once again thank you jschall.