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Mavic mini crash

fishiero

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Hi , pretty new to all this , had a 2nd hand mini bought for me for my birthday , flew it for a week or 2 with no problems, just the odd warning about a propeller rotating too fast , but last week flew it decided 8 mins into a flight to slowly descend down into the sea !! It was almost like it was returning to home but I've checked the video and home was where I was standing, is this a common fault that the drone loses communication, I could see the drone as was only about 50metres from me , I'll try and post the video , it's 7mins so have fast forwarded a bit, any advice would be appreciated, thanks
 

Macinfo

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Sorry it won't let me post the video
You'd have to post the video to YouTube or similar service and provide the link in your video in a new post. You may want find the log files from your flight if your familiar with that process..
 

slup

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...any advice would be appreciated, thanks

The vid isn't necessary to begin with ... the flight log is though. You usually have 2 useful logs recorded on the mobile device you flew with ...

Start up by attaching the mobile device .TXT log from that last flight in a new post here.

Read up here on how to retrieve it (read under section 3.) --> Mavic Flight Log Retrieval and Analysis Guide
 

slup

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Yep ... this was another of the dreaded "Uncommanded descent" cases that the Mini 1 is so famous for ... this originate from deformed props (usually the rear ones) not able to create enough thrust. This makes the motors spin faster to make up for the lost thrust ... that in turn generates all those hundreds of errors as per below you got already from 33sec into the flight, one of the messages clearly says what's going on ...

(Click on pictures & charts to make them larger)
1617228544091.png
This also generates a very bad AC pitch ... leading to heading speeds below what's specified, this is also seen during this flight.

When the thrust becomes even lower the motors eventually reach their max rpm's ... from there it's game over. The AC don't react to forward flight commands any longer, as seen here in the last seconds of flight when the AC goes backwards even though you command full right stick forward. At this point the AC is also losing height fast ...

Here a chart that shows the uncommanded descent ...

The blue is height from HP
The orange is vertical speed (positive values is descent)
The grey is you throttle stick (left stick forward/backwards) value 1024 is neutral

As seen in the last half of the chart... you applied several full ascend commands but the vertical speed stays positive for descending & the AC lose height with 4-5mph.

1617229024292.png

It's really surprising that you didn't react to all error messages at all ... they started to pour in already from 33sec into the flight ... but you kept on flying?

In the past when the Mini 1 was newly released this was very common & DJI took responsibility for them back then ... don't have a clue how they will act in your case. With all these error messages this is border lining to a pilot error.
 
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Macinfo

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Couple things of curiosity on this incident.. One I guess based on the video of the flight, is the drone gone and unrecoverable? I did not see it mentioned, though it seems like it might be, but never having been there, perhaps it is recoverable??

@slup, you noted that this is an "dreaded" issue, based on deformed props, so is the fix to replace the props as the originals were defective, or do they begin to fail over time and should be routinely replaced on the Mini 1?
 

BossBob

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The mini 1 props deform during storage. My understanding is that having them crossed under the body places pressure in them, flattening them.
 

slup

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...so is the fix to replace the props as the originals were defective, or do they begin to fail over time and should be routinely replaced on the Mini 1?
As said, the props deform (flattens) mostly during storage ... sometimes even being deformed already from the box the Mini 1 came in when it was new. Then later from storing it in the original case with the props folded. Even new props have been reported to being deformed straight out from the package ...

Don't remember now from which firmware DJI put in a over revving warning with the recommendation to put on new props ... but it's there now. When that warning came in it was a laud outcry that this warning must be a bug as several just couldn't find any props that didn't generated this warning ... so the props for the Mini 1 is a major design flaw & needs to be monitored constantly. As soon as the craft no longer can pitch down enough to produce air speeds according to spec the props needs to be changed, at latest ... otherwise the next that will happen is what we have seen in this case, it starts to lose lift.

A tip to all Mini 1 users ending up in a situation like in this case ... when a forward speed can't be achieved anymore, or every attempt to go forward make the craft starting to descend (due to that the rear props have lost to much thrust & can't pitch the craft down) is to fly home backwards ... as then it's the front props that generates the pitch. And take this decision early, as other wise the descending speed will increase to much & the deformed props can't stop it.
 
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Macinfo

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Thats interesting as I know a couple people looking to save a few $$ for a Mini 1, this sounds like a relatively serious issue, are there 3rd party props that do not have this issue for the Mini 1 that can be relied on? Otherwise may just tell them to move to the Mini 2 and call it a day if they intend to buy soon...
 

NDWildBill

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A major clue to what happened here is in the first sentence of the original post: " just the odd warning about a propeller rotating too fast." I'm guessing these warnings were ignored.
 
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slup

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...Otherwise may just tell them to move to the Mini 2 and call it a day if they intend to buy soon...
...first sentence of the original post: " just the odd warning about a propeller rotating too fast." I'm guessing these warnings were ignored.
Yeah ... the warning was ignored that's why this happened ... & that warning is what brought down the intensity of all these incidents a year ago, people usually don't ignore warnings even though they don't like them in the beginning.

The Mini2 is a much better craft in this regard & others also ... if the $$$ is there or can be saved up I would go with the 2 every day.
 

Zbip57

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fishiero

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Hi , thanks so much for going through the log , I've had those warnings come up now and again, I had already brought the drone back to home for that warning before this last flight, I've recovered the drone, dried it out but it's not playing! Have just bought a replacement drone, put it up in the garden just now , 10 ft up in the air, same warning about rotating too fast , seems like it's a common fault/warning! Do new blades need to be fitted?
 

fishiero

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Another warning that always comes up is weak signal, the drone is only 50 metres away sometimes, all these warnings, it'd never fly anywhere , yeah I'm new to it but they don't seem too reliable
 

fishiero

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Couple things of curiosity on this incident.. One I guess based on the video of the flight, is the drone gone and unrecoverable? I did not see it mentioned, though it seems like it might be, but never having been there, perhaps it is recoverable??

@slup, you noted that this is an "dreaded" issue, based on deformed props, so is the fix to replace the props as the originals were defective, or do they begin to fail over time and should be routinely replaced on the Mini 1?
I indeed have recovered the drone , have dried it out but it's not playing ! Looks like new blades to be fitted nearly every time it gets used
 
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