DJI Mini 2, Spiral out of control, 2022-02-15

[sar104]

I'm sorry about my tardy response; our travel schedule got really hectic our last week here in South Africa and just now got back on track! Such awesome analysis!!! I'm an engineer and I wish I got to do this type of stuff at work hahaha. It's very interesting to see how "special" my accident was haha. Also, and I didn't mention this before, but it was an officially refurbished drone by DJI. I didn't think much of it at first, but coincidence?

Anyways, I don't know much about the inner workings of drone components and their interactions, so I don't know if the IMU misbehavior that "slup" was talking about earlier would account for the [Integral of z-speed over time] difference vs [OSD_height] (and how is that measured independently? GPS?), but it is clearly out of whack.

The z-axis accelerometer is part of the IMU. The velocity solution is primarily based on the accelerometer data, while the height is corrected by barometer data - that's why a discrepancy between those quantities shows up if one is giving incorrect values. It could have been a hardware or a processor issue.

I can imagine how that one malfunction can happen, but it seems almost impossible that a propeller would come off exactly during the same flight? Or that the defect in the sensors was enough to trigger an unusually aggressive behavior that unscrewed the propeller?

That's a good question, and I don't have a satisfactory answer. I don't like combinations of independent low-probability failures.

One more thing that is probably unimportant (since no one commented on it), but on the original post I said in passing: "I was able to keep it high up until I thought to click return to home [the H button on the remote] when it very quickly lost all control and went for a free fall into the nearby pond...". I just want to make sure this comment wasn't missed, but it felt like as soon I as pressed that button (which seems really dumb in retrospect), it went tumbling down.

I saw your comment on that, but the aircraft never entered RTH - it was in P-GPS mode until 103 seconds, when the final spin triggered it to go to ATTI.

Good news to finish up, though! After the initial conversation here on the forum, I reported the incident to DJI, they got back to me within a few hours and confirmed it was a malfunction of some sort and they would send me a new one. I tried digging a little deeper for answers, but they just provided an empty bureaucratic response...

"Based on the analysis result, it seems that the incident was caused by a possible propulsion issue. However, as the aircraft was lost and we could not get it for further analysis, that was only one of our speculations. Since there was no pilot error discovered, we determined to cover this case under warranty."

Anyways, I just received a new one in the mail today!

That's the correct conclusion by DJI - I'm pleased to hear that they replaced it.