DJI Mini 3 Unknown Crash

[gleavitt513]

Was enjoying a flight with my mini 3 today, hovering over a park, when suddenly I get a message on my controller, "Motor Unable to Rotate" So I decide to bring it in. It then starts acting very wonky, flying all over the place, and the controls feel odd. I was doing my best to keep it over grass and not not hit somebody's house, but it starts an uncontrollable forward-left flight, despite my control inputs doing the exact opposite. It then crash landed into someone's chain-link fence on there lawn, where a person was working. I was lucky it didn't hit him. I retrieved the drone, and it had no physical damage besides some scratches, scuffs, and a broken prop. I have my doubts that this was user error, as even though I'm 15 I've been flying drones since I was 6 and know what I'm doing. Although, I'm not opposed to any possible errors that occured on my end. The video of the crash started right after the initial motor error prompt was given, and the drone had started its forward-left flight.

HELPFUL NOTES:

Master Airscrew Super Stealth Props were installed.

Winds were about 15-20mph if I had to guess.

The propellor that came off broke off, so I know it wasn't the prop screw that failed.

When I retrieved the drone, both back motors felt rough when rotated with my fingers, almost like a "crunchy" feel, although this may have been from the impact itself.

The propellor that broke off was one on the right rear arm.

Prop that broke off was found at crash site, so not a prop failure either.

In Flight log, errors start at 14:50

CRASH VIDEO:

https://drive.google.com/file/d/1pqOS1yIA6g1r20Ti1ccUwqYJXaVaoftG/view?usp=drive_link

FLIGHT LOG:

DJI Flight Log Viewer - PhantomHelp.com

 

[mavic3usa]

MAS better start getting their act together; tired of hearing about their props snapping.

 

[gleavitt513]

MAS better start getting their act together; tired of hearing about their props snapping.

The prop didn't snap until the impact, as it was found next to the drone, i forgot to add that detail.

 

[GFields]

https://drive.google.com/file/d/1pqOS1yIA6g1r20Ti1ccUwqYJXaVaoftG/view?usp=drive_link

Request Access is being asked on your Google Drive link. Upload to YouTube and embed the video

 

[gleavitt513]

Okay. Never done this before, sorry for any inconvenience.

 

[GFields]

I am not an expert when it comes to analyzing flight data. However, I did see several mistakes you made including flying higher than the maximum legal altitude in very windy conditions. When you got the warning about high winds instead of lowering the altitude you flew higher.

@Meta4 @slup are very good at assisting. So hang tight they will jump in.

 

[gleavitt513]

I was relatively low, when the motor error occured, and Ive flown in windy conditions maybe hundreds of times before with no issues. I dont think the high altitude ascent had anything to do with the motor error. Ive flown the mini 3 quite a bit, and know what its capable of, the strong wind warnings are typically given prematurally.

 

[gleavitt513]

Request Access is being asked on your Google Drive link. Upload to YouTube and embed the video

How do i embed the video? Its uploaded to youtube. I could just send a link.

 

[GFields]

How do i embed the video? Its uploaded to youtube. I could just send a link.

Click share, copy the link, and paste the link into the body of a post

 

[slup]

If looking into the moment where you get the "Motor unable to rotate" error, we see several uncommanded movements that could point to a loss of thrust (for instance, the motor can't rotate as fast as it's commanded).

The error come at 890sec into the flight... have in below chart placed a chart marker there.

The dashed graphs is the stick commands, & have chosen the same color for the stick & attitude axis to make it easier to compare the command vs. the attitude change.

We see that at 890sec the drone uncommanded rapidly rolls to the right side & pitch up (or drops the rear)... this indicate a problem from the rear right corner. At the same time the drone also rotate about 180 degrees CW while the rudder stick is in neutral position... this again points to the rear right as that corner is applying a CCW rotational torque, if that fails to keep up with the 3 other props torque wise, the drone will rotate CW.

So it seems like the error is correct, something is preventing the rear right motor to rotate as commanded by the flight controller. And probably it's due to debris as the motor problem seems to be intermittent... if the motor was constantly blocked or forced to rotate slower, the drone would have rotated CW constantly while falling.

(Click on the chart below to make it larger, the meaning of the graphs is in the legend below the chart & the values is from where the chart marker is placed at 890sec)

 

[gleavitt513]

Click share, copy the link, and paste the link into the body of a post

Here's the video link.

 

[gleavitt513]

If looking into the moment where you get the "Motor unable to rotate" error, we see several uncommanded movements that could point to a loss of thrust (for instance, the motor can't rotate as fast as it's commanded).

The error come at 890sec into the flight... have in below chart placed a chart marker there.

The dashed graphs is the stick commands, & have chosen the same color for the stick & attitude axis to make it easier to compare the command vs. the attitude change.

We see that at 890sec the drone uncommanded rapidly rolls to the right side & pitch up (or drops the rear)... this indicate a problem from the rear right corner. At the same time the drone also rotate about 180 degrees CW while the rudder stick is in neutral position... this again points to the rear right as that corner is applying a CCW rotational torque, if that fails to keep up with the 3 other props torque wise, the drone will rotate CW.

So it seems like the error is correct, something is preventing the rear right motor to rotate as commanded by the flight controller. And probably it's due to debris as the motor problem seems to be intermittent... if the motor was constantly blocked or forced to rotate slower, the drone would have rotated CW constantly while falling.

(Click on the chart below to make it larger, the meaning of the graphs is in the legend below the chart & the values is from where the chart marker is placed at 890sec)
View attachment 174567

this makes sense...it also makes me wonder if I did some user error as well. if you look at the crash video, from the camera angle, it looks as though the drone was flying forward and to the right, and if you look at my stick movements, i was doing the exact opposite, full backwards and left pitch. Now, if the drone rotated 180 degrees, that means it was flying backwards, as also seen in the flight log. So the drone was following my commands exactly.....I was just looking at the camera angle, which appeared to be going in the forward-left movement. So that makes me wonder, if in the initial "motor error" prompt, the sudden unexpected rolling from the malfunctioning motor caused the gimbal to freak out, and also turn 180 degrees, making the picture on my phone also rotate, and thus caused the controls to be reversed from the drone's perspective. I guess I didn't notice the change because the camera was pointed all the way down. So my attempts to go backwards/correct were successful, I was just flying with the controls reversed from the drone's perspective.

 

[slup]

this makes sense...it also makes me wonder if I did some user error as well. if you look at the crash video...

The video seems to show the very end of the flight, approx. the yellow circled area... the motor error & what's described in the chart in post #10 happens in the white circled area.

 

[Frank071]

The video seems to show the very end of the flight, approx. the yellow circled area... the motor error & what's described in the chart in post #10 happens in the white circled area.

It would be interesting to see footage from that moment, as the log also shows the drone rolling completely to the right (as @slurp pointed out) within 0.4s after the message:

I am wondering if the drone got hit by something (like a bird) - not sure if a drone would do such a quick roll on motor failure alone

 

[gleavitt513]

That's definetly a possibility. The drone must have moved out of the gimbal's range during the roll, because for a split second, I saw a weird uncontrolled movement on my phone. Also, holding that thought, the rest of the crash couldve been user error, because the gimbal flipped all the way around; effectively reversing my controls from the drone's perspective, leading loss of control and crash. I didnt notice the gimbal flip, because the camera was pointed all the way down. You can especially notice this in the flight log, where the drone appears to be flying backwards after the motor error, where the crash video looks like it is flying forwards.

 

[TonyPHX]

That's definetly a possibility. The drone must have moved out of the gimbal's range during the roll, because for a split second, I saw a weird uncontrolled movement on my phone. Also, holding that thought, the rest of the crash couldve been user error, because the gimbal flipped all the way around; effectively reversing my controls from the drone's perspective, leading loss of control and crash. I didnt notice the gimbal flip, because the camera was pointed all the way down. You can especially notice this in the flight log, where the drone appears to be flying backwards after the motor error, where the crash video looks like it is flying forwards.

So few people are willing to acknowledge user error. Kudos to you for being aware of all options.

 

[gleavitt513]

Just conducted a test flight with stock props. Seems to fly alright, will keep an eye on it for awhile. Thank you everyone for your help!