Mavic Mini took a swim: analysis needed please

[heiterman]

Flew a great flight out along a jetty and followed a boat coming back east into the harbor. Weather was great, minimal to no wind. No battery issues. No warnings that I recall. Great sat locks and never lost any reception. About 12 min in I was on my way back to base, about 2000 ft out and noticed a small uncommanded decrease in altitude at about the 12 min mark. I gave the mini a short up on the stick to correct. A few moments later to my horror it started a sustained and uncommanded descent into the bay. It happened so fast! I think I was about 15-20 feet in altitude before it descended without any control input.

I am no telemetry expert, however reviewing the .dat file using my google aeronautical degree I didn't see anything that stuck out. I'm going to escalate to DJI soon but wanted to see if any experts here could take a peak to see what the heck caused this to happen.

Along with the loss of the drone, the biggest disappoint and lesson learned is to not keep camera footage from an entire trip on one card. Lesson learned! The footage I lost from the previous days of flying and filming really stung

Thank you for all your help,
Brian

CLICK HERE: Airdata flight link

 

[Meta4]

Thank you for all your help,

Could you just post your .txt file?
That would make it a lot easier to see what happened.

 

[heiterman]

I think I found the right .txt file. Here you go. I also uploaded the .txt
to Airdata.

I looks like I was applying up stick to try to keep altitude for the last 30 sec or so without success?

I appreciate any incite before I contact DJI.
Thank you!

Airdata .txt file

 

[Meta4]

I think I found the right .txt file. Here you go

Much better .. thanks
This will show your flight data much better:

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

Your flight data shows altitude stability issues slowly developing toward the end of the flight (after 11:36.0) which ended with an uncommanded descent from 45 feet.
Pushing the left stick forward for two seconds from 12:06.1 made no difference and the descent continued into the water.

Early on the the Mini's history uncommanded descents were a real and serious issue until DJI released version 1.0.5 firmware to correct the problem.
But your Mini was running Firmware 1.0.5.

This looks like a good case for a warranty claim
I'd suggest synching your flight data to upload it to DJI's servers.
Then talk to their online support people who will help you get the ball rolling.
The data should be sufficient to support your claim even though you don't have the Mini to return to them.

 

[BadWolf1]

I looked at this last night and the last two messages in the DAT file are
741.062 : 41255 [L-FDI][CTRL]: fault on , height_ctrl_fail
741.082 : 41256 [L-RC]craft ctrl failed!!!

That reinforces what @Meta4 says, and I'd follow the advice to pursue a warranty claim.

I know @sar104 has studied the patterns in uncommanded descents and might see more in the log

 

[Motorcycle Rider]

Welcome to the forum, sorry for your loss of the mini.

 

[sar104]

I looked at this last night and the last two messages in the DAT file are
741.062 : 41255 [L-FDI][CTRL]: fault on , height_ctrl_fail
741.082 : 41256 [L-RC]craft ctrl failed!!!

That reinforces what @Meta4 says, and I'd follow the advice to pursue a warranty claim.

I know @sar104 has studied the patterns in uncommanded descents and might see more in the log

It was uncommanded descent due to lack of rear prop thrust. It's clearly apparent at 695 seconds, but recovers, and then again, terminally, at 730 seconds. Left back motor command has gone to 100% and the pitch has dropped, even under full elevator, but there is insufficient thrust to prevent the descent.

 

[Flygmaskin]

Sorry to hear about this incident. Valuable and tough lesson to learn about keeping valuable photos from several days on the SD-card.

Regarding the loss of your AC, I’m pretty confident that you will get a warranty replacement if you contact DJI. The data provided can’t be contested.

 

[heiterman]

I greatly appreciate the data review from the members who responded. I've been lurking on this forum ever since my purchase, I just never had a need to post. I will update the post as DJI responds. Thank you again for all of your help!

 

[Cw4bray]

It was uncommanded descent due to lack of rear prop thrust. It's clearly apparent at 695 seconds, but recovers, and then again, terminally, at 730 seconds. Left back motor command has gone to 100% and the pitch has dropped, even under full elevator, but there is insufficient thrust to prevent the descent.

View attachment 106116

I'm wondering if an emergency procedure, would help ? It probably happens very quickly and would require extremely quick wits. How about, if you induced yaw, to place the rear blades in clean undisturbed air ? After recovery, regain altitude fly home with camera facing aft. Then replace blades. ?

 

[sar104]

I'm wondering if an emergency procedure, would help ? It probably happens very quickly and would require extremely quick wits. How about, if you induced yaw, to place the rear blades in clean undisturbed air ? After recovery, regain altitude fly home with camera facing aft. Then replace blades. ?

Maybe. As I reported previously, I was easily able to reproduce the problem but I did not find any way to stop the descent once started. However those tests were not completely exhaustive, of course.

 

[heiterman]

I wanted to round back with the forum members who helped tremendously with data analysis. After submitting a ticket with DJI and jumping through quite a bit of hoops with multiple agents asking for the same information multiple times, DJI came to the same conclusion as the forum - the unexplained loss of altitude was the result of a "warranty case" and they will be replacing the mavic mini. I did ask them to see if they would be so generous as to also include a replacement battery as the original went down with the drone into the deep ocean. I didn't get a reply back from them yet. Bummer also about the loss of the memory card.

I have learned so much about the technology engineered into these products. Absolutely fascinating! Unfortunately, I seem to have lost a lot of confidence in the airworthiness of the mini and don't really know what it will take to have trust in it again. When I first saw it descent into the sea, my heart sunk so much thinking I just lost $400 (ouch!). I'm glad DJI pulled through and hopefully they will get to the bottom of why the mini has a pretty excessive record, at least anecdotally, of uncommanded descents.

Thank you again folks!!

 

[Flygmaskin]

I wanted to round back with the forum members who helped tremendously with data analysis. After submitting a ticket with DJI and jumping through quite a bit of hoops with multiple agents asking for the same information multiple times, DJI came to the same conclusion as the forum - the unexplained loss of altitude was the result of a "warranty case" and they will be replacing the mavic mini. I did ask them to see if they would be so generous as to also include a replacement battery as the original went down with the drone into the deep ocean. I didn't get a reply back from them yet. Bummer also about the loss of the memory card.

I have learned so much about the technology engineered into these products. Absolutely fascinating! Unfortunately, I seem to have lost a lot of confidence in the airworthiness of the mini and don't really know what it will take to have trust in it again. When I first saw it descent into the sea, my heart sunk so much thinking I just lost $400 (ouch!). I'm glad DJI pulled through and hopefully they will get to the bottom of why the mini has a pretty excessive record, at least anecdotally, of uncommanded descents.

Thank you again folks!!

Thank you for updating the progress in this case. Glad to hear that DJI came through and will replace the AC.

I can easily understand your lack of confidence regarding the Mini. Who wouldn’t have doubts after your experience?

I’m nowhere near an expert on the subject of uncommanded descent, but I have understood it (from this forum and the extensive work produced by members here) that the phenomenon seems to be caused by the props being slightly deformed. In many cases the deformation seems to be caused by improper storage of the AC (IE using the stock Fly more case).

I would advise you to keep flying with caution (as one always should), and keep your props “straight” at all times. Don’t store it in a manner where the props could be bent. Find a bag/case with ample space or leave it out on a shelf or something.

My bet is that the Mini will fly just fine, as long as the props are ok you can trust it.