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Uncontrolled dropfall, help needed :/
804 39 1-19 12:21
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zemetras
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Hi guys, below is the video and I think correct fly log, drop happens somewhere around 7th minute.
No wind or really very weak not recognizable on ground, tempretaure ~ -2°C to -3°C
No expert here, but from the logs I did not do any crazy maneuvers, barely touching sticks.
Once I see drop I tried to push drone UP but it just drops straight and smashed ground.
Anybody willing to help with analyzis, please ?
https://www.phantomhelp.com/LogViewer/ZHBDWAJZUS53VZ4PGPSH/#


1-19 12:21
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DJI Stephen
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Hello and good day zemetras. I am sorry to read and to know what happened to your previous flight with your DJI Mavic Mini. Since this unfortunate issue happened. Kindly please contact out DJI Support Team for further assistance at https://www.dji.com/support?site=brandsite&from=nav. We would do their best to find out the reason of the incident and then the corresponding resolution would be provided. Again I am sorry for your loss and thank you for your understanding.
1-19 12:28
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fans461cbed1
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Have seen several Youtube movies with similar crashes of MM.
It's very clear to me:
MM doesn't like combination of cold with moisture.
1-19 12:30
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zemetras
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I have combo, this happens during flight  with 1st battery. Next 2 batterries (~40 minutes)  did not experienced drops.
Just quite a lot "max load" messages comes and goes.
When changing batteries, There was  a little bit of frost on propellers. Scratched with hands.
Only thing I could think of what was not OK. Still this drop was too big for a frost, I think if I pushed stick UP it should at least slow drop a little but it felt like a stone.
I think I will not fly anymore during low temperatures, too risky if this can happen anytime.
1-19 12:35
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DJI Stephen
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Thank you for the additional information you have provided zemetras. I will be providing a DJI Forum Thread created by hallmark007 titled Flying in Cold Weather. This might help you and our valued DJI co pilots on how to fly in cold locations ( https://forum.dji.com/thread-201739-1-1.html ). Thank you.
1-19 12:52
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jonny007
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Could also be an effect from frozen humidity at the vps sensors which has irritated them (and then initiated an auto landing). Just now discussed in the thread "unwanted AutoLanding"
1-19 12:56
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hallmark007
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Were you flying in heavy fog ?
1-19 12:59
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Miixxa
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Guess it was humid/fogged up and temperature at 0C or under?

That's exactly what happened to me too, with the exception that I got a Motor Error notice just before it started to plummit down. It seems you never got that message but your battery cells are going undervoltage at ~50% mark which would seem like something is sucking too much current out. That something being the motors trying to spin your iced up props.

I've attached a pic of what amount of ice buildup brought my bird to the ground, pic taken right after my Mini dropped. Not much needed, but those Mini motors are pretty tiny and have pretty much no torque... Continued flying fine and without errors right after I cleared the props from ice.
IMG_20200116_131321.jpg
1-19 13:11
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zemetras
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Same here, I got some ice on propellers too, not on the edges tho.
As mentioned before, drop > cleaned propellers > then no drops afterwards , just max load errors.
1-19 13:29
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hallmark007
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zemetras Posted at 1-19 13:29
Same here, I got some ice on propellers too, not on the edges tho.
As mentioned before, drop > cleaned propellers > then no drops afterwards , just max load errors.

That looks like sensor error maybe getting fogged up thought it was close to landing so initiated landing .
Will check log later
1-19 13:40
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Miixxa
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zemetras Posted at 1-19 13:29
Same here, I got some ice on propellers too, not on the edges tho.
As mentioned before, drop > cleaned propellers > then no drops afterwards , just max load errors.

Yup, seeing how finicky the Mini is with the props I'm confident that even a small amount of ice will cause enough stress for the motors and impair the efficiency of the props for this to happen.
It's a shame I didn't take a pic of the underside of the props, since there was a lot more ice buildup with like a "turbulator" pattern which I can imagine to severely affect the lift and resistance of the props...

Just stay clear of flying in freezing temps combined with high humidity, and no problems
1-19 13:46
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Jake Phantom 3 S
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My guess to all these drops is icing on the propellers, this will certainly bring it down. Same thing happens to passennger airlines. There have been plane crashes because of icing on the wings. Watch for it in cold weather.
1-19 13:47
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zemetras
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Thanks for replies guys, definitely I will be more carefull with low temperatures ( I will not fly to be exact ).
One thing is strange, as mentioned, I continue to fly  after drop, there was again slight ice frosts on propeller, but such a drop did not reoccur again .
Also checked "unwanted landing" thread but I was not that low, also did not push stick DOWN at all as could be seen in the logs.
Thanks again anyway.
1-19 13:56
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Miixxa
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zemetras Posted at 1-19 13:56
Thanks for replies guys, definitely I will be more carefull with low temperatures ( I will not fly to be exact ).
One thing is strange, as mentioned, I continue to fly  after drop, there was again slight ice frosts on propeller, but such a drop did not reoccur again .
Also checked "unwanted landing" thread but I was not that low, also did not push stick DOWN at all as could be seen in the logs.

My best guess is that you just happened to accumulate more ice on the first flight.
At least for me the drone was flying fine when I just flew it around for like 100m radius and under 25m. After I did a maxxed out dronie, the craft returned to starting position, immediately triggered the motor error and plummited towards me no matter what I did with the sticks... So I guess there was just that much more moisture/coldness higher up that it iced up the props. Who knows, but I continued to fly with the same battery and under 25m for 10mins after that w/o problems.

Also that clearly isn't an landing of any kind, your craft came to the ground much faster than it could even in Sport mode, so it flatout dropped. The footage and dropping speed is pretty much identical with mine...
1-19 14:20
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Pologc89
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Hello, just let me know, do you have put on the propeller guard , cause I thing the problems comes  from there, I had exactly the same problem and the weather in here was about the 15°c, and I read that maybe that is the problem. The propeller guards are only designed for indoor flights.
1-19 18:56
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GaryDoug
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I doubt the Mini "thought" it was landing or it would have swung up the camera before impact.
1-19 20:33
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German DroneTV
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Miixxa Posted at 1-19 13:11
Guess it was humid/fogged up and temperature at 0C or under?

That's exactly what happened to me too, with the exception that I got a Motor Error notice just before it started to plummit down. It seems you never got that message but your battery cells are going undervoltage at ~50% mark which would seem like something is sucking too much current out. That something being the motors trying to spin your iced up props.

I think there is establishing ice in the engines at cold and fogy weather conditions.
Same happend to me with motor error (dropping from minute 1:10):



1-19 21:00
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zemetras
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Hello, I did not use propeller guards.
If similar drop happend to you in ~+15°C , then I think we have another FW issue hq :/
1-19 21:00
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AntDX316
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zemetras Posted at 1-19 21:00
Hello, I did not use propeller guards.
If similar drop happend to you in ~+15°C , then I think we have another FW issue hq :/

1-19 21:36
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InspektorGadjet
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Well the drops I have reported were all done in temperatures between 10 and 15 degrees Celsius, no icy conditions.
Something else is going on.
1-20 04:26
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Minnesota
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I looked at bit closer at the log, in both AD and FRAP. Nothing jumps out other than a ton of Not Enought Force errors for over a minute before the fall.



NEF.jpg
1-20 06:18
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InspektorGadjet
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AntDX316 Posted at 1-19 21:36
https://www.youtube.com/watch?v=mc3U_qAxOcc

Crazy, thanks for sharing!
Still the drops on my mini were in non icy situations.
1-20 06:34
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jonny007
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zemetras Posted at 1-19 13:56
Thanks for replies guys, definitely I will be more carefull with low temperatures ( I will not fly to be exact ).
One thing is strange, as mentioned, I continue to fly  after drop, there was again slight ice frosts on propeller, but such a drop did not reoccur again .
Also checked "unwanted landing" thread but I was not that low, also did not push stick DOWN at all as could be seen in the logs.

I didn't mean that you were too deep, but that the vps sensors were damp and icy and irritated by it, as if you were really deep. This as another possible cause.
I can't imagine that very little ice on the propellers will cause an instant crash. Unstable flight behavior certainly, but that the drone suddenly falls like a stone ?
1-20 09:16
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jonny007
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Minnesota Posted at 1-20 06:18
I looked at bit closer at the log, in both AD and FRAP. Nothing jumps out other than a ton of Not Enought Force errors for over a minute before the fall.

Also interesting the Autolanding at 7:26 ... immediately before the impact.
1-20 09:20
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hallmark007
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jonny007 Posted at 1-20 09:16
I didn't mean that you were too deep, but that the vps sensors were damp and icy and irritated by it, as if you were really deep. This as another possible cause.
I can't imagine that very little ice on the propellers will cause an instant crash. Unstable flight behavior certainly, but that the drone suddenly falls like a stone ?

This craft landed because of sensors , in the log it reads adv landing but I can’t find out what that is .
1-20 09:22
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ChRoM
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For what it's worth: ice buildup on the propellers after flying in cold and foggy conditions. While I wouldn't tisk this again (I was young and stupid and too bold), the MM performed flawlessly. Didn't fly the battery below 50 percent though.
1-20 10:11
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fracz
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Also tried fog-flying some time ago and managed to get a nice sunrise footage. However, I was pretty sure it were above 0 degrees but then when I returned to the car it showed me -6! O_O

2020-01-20-19:25:26.png

Reckless flying from my side... but worth it, and luckily, mini landed safely :-) The first hyperlapse on this compilation is from this fog:




1-20 10:29
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m80116
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Well... I managed to mince a straw of grass with my 2nd Mini on take off (rear props)... after that it refused to take off and bounced reducing the speed of the motors.

If that was a plane I'd say it was almost past V1... absolutely rebukable logic.
1-20 16:50
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Gray Volk
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Hard landing is an interesting way to shake off the ice, I must say.  Glad it ended well.
1-20 17:09
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zemetras
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That is what I thought after info from this thread : don`t fly in cold, but if you will, just smash drone to the ground from tiume to time to defrost
1-21 09:12
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JJB*
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hallmark007 Posted at 1-20 09:22
This craft landed because of sensors , in the log it reads adv landing but I can’t find out what that is .

Hiya,

Translated wrong by the decrypter :  NaviAdvLanding = an Quickshot mode

VPS did not gave false altitude measurements, i think too that is was icing on the blades. Scary to see it drop like this!

cheers
JJB
analysis1.png
1-21 09:24
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Minnesota
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JJB* Posted at 1-21 09:24
Hiya,

Translated wrong by the decrypter :  NaviAdvLanding = an Quickshot mode

"Translated wrong by the decrypter" - where is this done? I saw it in one of the csv files.
1-21 10:01
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hallmark007
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JJB* Posted at 1-21 09:24
Hiya,

Translated wrong by the decrypter :  NaviAdvLanding = an Quickshot mode

I have tested mini in cold weather and the one thing you will clearly notice when flying in cold weather is first you get a warning which almost covers your screen and tells you not to fly if you continue you will get continuous warnings in black telling you temperature is to low, I tested in -3 to -5 and the results was craft involuntary rising in altitude and lowering in altitude. I flew craft for full battery which only lasted 21 minutes.

My conclusion was cold temp was affecting the IMU , but at no time was there anything like we seen on video above , that’s why I thought it might be sensor related, he didn’t receive any temp warnings against at least 20 I received .
1-21 11:26
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jonny007
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hallmark007 Posted at 1-21 11:26
I have tested mini in cold weather and the one thing you will clearly notice when flying in cold weather is first you get a warning which almost covers your screen and tells you not to fly if you continue you will get continuous warnings in black telling you temperature is to low, I tested in -3 to -5 and the results was craft involuntary rising in altitude and lowering in altitude. I flew craft for full battery which only lasted 21 minutes.

My conclusion was cold temp was affecting the IMU , but at no time was there anything like we seen on video above , that’s why I thought it might be sensor related, he didn’t receive any temp warnings against at least 20 I received .

Makes sense assuming to this video. Not a dramatic effect as I thought, but it shows that the IMU system is generally temperature sensitive. Another interesting statement: Perform the IMU calibration in the "temperature environment" in which you fly. Conversely, perhaps you could say: If you want to fly below 0 degrees, calibrate the IMU at 0 degrees, but best would be not to fly ;-) AND the manual says the operation temperature range should be 0 to 40 degrees C or 32 - 104 F

1-21 12:04
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hallmark007
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jonny007 Posted at 1-21 12:04
Makes sense assuming to this video. Not a dramatic effect as I thought, but it shows that the IMU system is generally temperature sensitive. Another interesting statement: Perform the IMU calibration in the "temperature environment" in which you fly. Conversely, perhaps you could say: If you want to fly below 0 degrees, calibrate the IMU at 0 degrees, but best would be not to fly ;-) AND the manual says the operation temperature range should be 0 to 40 degrees C or 32 - 104 F

https://www.youtube.com/watch?v=KMTJVyBQLag

I think it’s always a good idea to calibrate to your normal flying temperature, but going below manufacturers flying temp might not be the best idea, I was in Sweden when I tested so it was pretty cold, not so cold here in Ireland .

But no I didn’t have sudden drop like we see in the video above .
1-21 12:12
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JJB*
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Minnesota Posted at 1-21 10:01
"Translated wrong by the decrypter" - where is this done? I saw it in one of the csv files.

Yes,  CSV files are representing the decrypted flightlog.txt files.  Just open a flighrecord.txt file and you see unreadible text....

1-21 12:24
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JJB*
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hallmark007 Posted at 1-21 11:26
I have tested mini in cold weather and the one thing you will clearly notice when flying in cold weather is first you get a warning which almost covers your screen and tells you not to fly if you continue you will get continuous warnings in black telling you temperature is to low, I tested in -3 to -5 and the results was craft involuntary rising in altitude and lowering in altitude. I flew craft for full battery which only lasted 21 minutes.

My conclusion was cold temp was affecting the IMU , but at no time was there anything like we seen on video above , that’s why I thought it might be sensor related, he didn’t receive any temp warnings against at least 20 I received .

Its not really cold in my country, live close to the sea so lots of time too much wind to fly my MM.

Once its minus 5 and no wind i will do some cold weather testing, guess sweden is a better place to do that
1-21 12:32
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fans461cbed1
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Miixxa Posted at 1-19 13:11
Guess it was humid/fogged up and temperature at 0C or under?

That's exactly what happened to me too, with the exception that I got a Motor Error notice just before it started to plummit down. It seems you never got that message but your battery cells are going undervoltage at ~50% mark which would seem like something is sucking too much current out. That something being the motors trying to spin your iced up props.
[Image]
Problem is not the motors but the aerodynamic airfoil of the props getting disturbed by the ice building up. This will reduce the lift created by the props.
1-21 15:31
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m80116
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I'd like to make me a winter flying kit for the MM.

  • Anti-icing fluid to coat the propellers with.
  • Bubble plexiglass dome over the gimbal, to protect it from cold and moisture.

I am wondering if I could use an original sepia gimbal cover and modifiy it or order some other gimbal guard from Ax and start from that. I already have the motor covers that might help somewhat.

I'd say something that could allow the tiny creature to fly comfortably until -10°C, providing the battery has been pre-warmed to a safe level.
1-22 02:16
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Miixxa
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m80116 Posted at 1-22 02:16
I'd like to make me a winter flying kit for the MM.

I'd just not fly it in those temps.
My experience is that anti-icers don't really work for props with relatively high air speed, also more potent de-icers may damage the props? I guess a silicon oil or maybe some kind of nanosealing could work better...
Bubbles will cause horrible distortions and glare on the footage, but it may very well help keeping the gimbal warm with the generated internal heat. Keep in mind that flying with such gimbal cover may cause overheating of the drone, since Mini get's all it's cooling air from the gimbal bay (probably not a problem at such low temps though).
I'd say the OEM cover could be a great starting point, if you hack everything off from the inside to allow free movement of the gimbal and replace the front face with clear 'something'. I say something cause most plastics have horrible optic properties and glass might be too heavy...

@fans461cbed1 I know it's nt the motors themselves, but ice build lowers the prop efficiency  while increasing the draq and weight of the props. Lowered efficiency means the control unit amps them up until they run out of juice and th craft descends, added weight and draq cause the motors to top out even sooner.
1-22 07:25
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