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Mavic Mini altitude drop without RC input
2482 28 2020-1-4
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fracz
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Reading all the problems about crashing and falling Minis, I really pay attention to mine Mini's behavior.
Yesterday I have noticed that it suddenly dropped in altitude almost 2 meters. And because I was flying approximately 3 meters above the water... It was quite stressful. Fortunately, full throttle up on the left joystick made the Mini go up and nothing happened.


The app shows that the mini knew it was going down (the altitude changes from -0.9m to -2.7m) so it is not a sensor problem. Wind was approx 15 km/h (according do UAV Forecast). Neither strong wind warning nor "not enough power" warning was displayed in the app.

My question is: is this a normal behavior of the drone and something I should always anticipate and prepare for, because it just "may happen" from time to time? Or is it a one of "I have no idea what I'm doing" Mini's behavior? ;-)

See the screen record (the mini drops when I switch from photo to video mode):



Flight log: https://www.phantomhelp.com/LogViewer/7J1D3C9Z2VV322UQNRIH/

The described situation is between 7m15s and 7m20s.
2020-1-4
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lannes
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I think I  read in another thread that someone else also had a drop when they changed camera modes over water, must be a bug in the app
2020-1-4
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JJB*
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Hiya,

Its not a bug, the MM downward sensor lost its reference for short while.

Flying low over water is risky beacuse of this, but good recovery!!
See ID 4340 where 1.7 meters > 'nothing' > 1.4.
cheers
JJB
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2020-1-4
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fracz
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Thank you JJB* for your fast diagnosis!

Does it mean that the drone positions itself based on the VPS sensor only? I always thought it has some sort of barometer for calculating its height.

So how did it know it was goig down and why it did not taken these data into consideration? The ALT columns shows the values that were displayed in the app.
2020-1-4
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Shantok
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They all act a little funny over water. Flying close to the water you always need to be cautious. I also think the Mini really relies on the VPS, more than other crafts. When light gets low it really drifts compared to my other Mavics.  

Looks like a nice place for some cool footage.
2020-1-4
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fracz
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But the captures over water are sooo great.

Will pay attention to your suggestions. Some day, I will end up with a new "I lost my Mini" thread here, probably
Thank you guys!

And the place was really perfect. Also caught a great sunset this day :-)

Posted the ducks in other thread: https://forum.dji.com/thread-205897-1-1.html#post_2049781
2020-1-4
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hallmark007
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That is covered in the manual

2020-1-4
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speed_freakz
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I had the same problem , not sure  is it related  but your battery was 3.496v at the time when the drop occured, I had the similar readings when  my  drone  dropped , but my both  cells  were at 3.44. I was flying higher than you tho, at 40 feet.
Funny thing is that  none of my commands to pull drone up higher  were  registered  at log but I remember  holding stick  up for few seconds.

The  drop  is at 2:00min onwards


2020-1-4
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fracz
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@hallmark007 I know, I read it. But I have understood the phrase "Vision System cannot work proplerly" as "it might not be as steady as expected".

And now, when I'm understanding it for the 2nd time... It makes sense Something we should be aware of.
2020-1-4
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jonny007
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fracz Posted at 1-4 09:42
But the captures over water are sooo great.

Will pay attention to your suggestions. Some day, I will end up with a new "I lost my Mini" thread here, probably

Everything that is great, is either dangerous or prohibited. This is the case with many things. I have seen many successfull videos on youtube with flights close to water surface. Ok, perhaps there are hundreds more which were not postet, because they would show a diving mini. I have asked some people whether they have taped the sensors to prevent irritations from vps and they say no. So it generally seems to work good. And what I wrote in a recent thread, I think that the faster the speed, the better and hovering probably is not a good idea.
2020-1-4
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JJB*
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fracz Posted at 1-4 09:28
Thank you JJB* for your fast diagnosis!

Does it mean that the drone positions itself based on the VPS sensor only? I always thought it has some sort of barometer for calculating its height.

Hi,

Good question!  Barometric sensor is used for keeping the craft at flying height with (no RC up / down inputs ofcourse)

When lowering height to 0.5 meter the VPS height sensor triggers the Autoland protection, it will stop the down movement as commanded by the RC stick down.

Try for example this ; hover at 30 meters in Sport mode, fully RC stick down and see what will happen.
It will slow down its descend when getting in VPS range and stop before hitting the ground.

But somehow VPS sensor data is used when flying low...if it looses it reference funny things to happen.
But flying at 8 meter height over an obstacle it will do nothing if the distance is > 0.5 meter.

without GPS signals the VPS down sensor is used for postioning, with good GPS signals GPS is used for this. But somehow within VPS range it looks like that this VPS sensor is also used, mayby as a fine-tuning referece to the GSP posioning?? who knows....

What i know only is that when the VPS sensor looses it reference....wait for the un-expected!  ;-)

cheers
JJB
2020-1-4
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DJI Stephen
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Hello and good day fracz. I am sorry for the trouble this has caused and thank you for reaching out. Can you please try to fly your DJI Mavic Mini to a different location to see if the issue will still persist? There might have been some interference on the place where you have flown your drone previously that is why this issue happened. Please keep us posted on the said issue for us to be able to assist you further. Thank you.
2020-1-4
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AlexanderN
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I also had a random altidude drop, fortunately not over water and at high altitude. However, it was the only one I had up to now so I think it will be hard to "reproduce" or to say that the issue does not persist, just from testing at another location.
2020-1-4
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m80116
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I don't get how it can be justified an almost 3 meters height loss.

I've read too many cases in which the Mavic Mini failed to recognize high winds and responded with lethargic counter manoeuvres or dropped unexpectedly.

Definitely a firmware glitch or wrong programming, it should and technically can ounter wind and drops much more aggressively.
2020-1-5
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PavelP
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Yes. It happened to me twice.
Once at about exactly the same conditions you described, but perhaps one meter higher in wind little stronger. According to airdata.net online log analysis it registered increase of barometric altitude prior to the event despite it was holding altitude perfectly before it started to descent.
Other event was more interesting. I was flying above field partially covered by snow without any problems for five or ten minutes to get used to drone. When I was flying in sport mode backwards at full speed i released controls before drone was about to cross ditch with dirt road. I'm not sure if i stopped because i've seen drone rapidly descending or it started to descent when i released joystick. In few seconds that drone was slowing down it dropped perhaps by five meters and almost crashed into opposite side of ditch (it almost seemed like it's following ballistic trajectory). Reading of barometric altitude is chaotic in log file (like 4.5m -> 6m -> -2m) and reading of downwards looking sensors seems ok. Drone ended likely 90cm above the ground (according to log, my guess is lower) and that ditch saved it. I was pretty sure it crashed before i looked onto camera image and realized I can still hear it.
It's quite scary because I almost crashed Mini three times and only once it was due to my stupidity. And problem is that Mavic Mini mostly behaves well even above the water or ice/snow covered lake.
2020-2-11
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djiuser_7cnLz028pnvs
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My first day out with the mini, I flew over a lake.

The mini was in the middle of the lake, and I had no hands on the controls, the drone was just hovering over the water when it just started to lower towards the water. My son shouted it going down into the water, I reacted quickly and brought it up to 40feet.

I am now nervous to bring it over water in the future.

Does anyone have an idea what would have happen there?
Thanks,
Gerry
2020-2-24
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Labroides
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djiuser_7cnLz028pnvs Posted at 2-24 15:45
My first day out with the mini, I flew over a lake.

The mini was in the middle of the lake, and I had no hands on the controls, the drone was just hovering over the water when it just started to lower towards the water. My son shouted it going down into the water, I reacted quickly and brought it up to 40feet.

As usual, the recorded flight data is needed to show what was going on during your incident.
Without data, all anyone can do is guess (and they'll probably be wrong).
2020-2-24
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PavelP
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Sadly I haven't found a way how to analyze log files from Mavic Mini and how to match SdrLog*.log and txt logs, but video with my two issues is here

and txt log files used in the video are here
https://drive.google.com/file/d/1H_5_WFwShO9ABUYpr-5a4yn5B7jbyejH/view?usp=sharing


2020-2-28
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PavelP
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PS: Video
0:31-0:39 altitude drop above water while turning (twice a bit, perhaps two or three meters in total)
(reaction: ops, pull up is on the left)
1:14-1:20 much faster altitude drop while going full speed in reverse (likely five meters or more)
(reaction: release everything ... hopefully it seems alive ... go up)
2020-2-28
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JJB*
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PavelP Posted at 2-28 10:42
PS: Video
0:31-0:39 altitude drop above water while turning (twice a bit, perhaps two or three meters in total)
(reaction: ops, pull up is on the left)

Hi PavelP,

Had a look at your second flight, flying low altitude above white snowy ground doesn`t give a good VPS height measuring/indicating. Moving fwd/aft stick form 100% fdw to 100% aft is not what a MM can handle quit well in Sport mode. Pitch values from down 34 to up 35 are flown. Hard work for the MM to keep the height at one height....So this does not look at the uncommanded descent but a 'habit' of the MM.
Mm is not a race drone but a small weight mayby little underpowered drone.

But happy that it did not flew into the ground, a little up command on the stick and MM did respond well.

Just my 2 cents.

cheers
JJB


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2020-2-28
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PavelP
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Thank you very much, JJB!
I found out that FRAP did not work cause i had CSV file that I somehow failed to convert with TXTlogToCSVtool.exe in the same directory as log files before finding and trying FRAP.
Flight over water is more obvious: it lost VPS readings as soon as it was about water and then it got somewhat random readings whenever it recovered.
On the other hand should drone take VPS readings into consideration to maintain altitude? Sometimes i would like to, usually I wouldn't. I'd like to have follow height above terrain feature for example to fly above the road uphill, on the other hand I don't want it to suddenly drop or raise by several meters, when it flies over something (e.g. river bank).
I'm not sure how barometer readings are reliable in conditions when relative speed of drone and air changes (e.g. drone changes speed from 40km/h forward to zero and 40km/h backwards, drone turns by 180° in 20km/h wind, sudden gust of wind, ...) and if there's a solution.
But ... i guess that drone has pretty good accelerometer and when it shows decrease in barometric altitude and 4m/s speed downwards it must be aware that there's something wrong. However I never had a warning about insufficient engine power or being close to this condition.
2020-2-28
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JJB*
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PavelP Posted at 2-28 23:14
Thank you very much, JJB!
I found out that FRAP did not work cause i had CSV file that I somehow failed to convert with TXTlogToCSVtool.exe in the same directory as log files before finding and trying FRAP.
Flight over water is more obvious: it lost VPS readings as soon as it was about water and then it got somewhat random readings whenever it recovered.

Hi Pavel,

Flying low over water with some speed ; yes  sometimes VPS height doesn`t measure the height, must be bad reflectings back to the sensor. I fly alot low over water, but always at low speed, had not yet any probem with height measuring. Enough about this to be read in the manual with cautions! and what not do do.

AFAIK VPS height (if withing range) is taken into account for height hold (like an assistence to the baro height signal), as seen in various logs when VPS measures intermittents things can go wrong regarding height holding.

Good question if barometric sensor is influenced by fast moves etc, many different opinions on this forum. I think yes a little and looks like that  Flight Control calculations are not that fast in combination (and/or) with little underpowerd motors....MM loose some height in extreme flight moves (sport mode full fwd to aft for example).

But my good news! :  when flying 'normal' MM does a great job flying perfectly!

PS some MM has other height hold problems, they loose power and droping uncontrolled in height. This is for DJI to solve!

cheers
JJB
2020-2-29
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djiuser_ot92D092RvOj
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My MM yesterday dropped from 9m height to 0 in almost no time. I was just moving forward at 6m height when I noticed it was actually ascending. So i left the right stick, and right after I could see the MM going down, until it crashed on the ground (fortunately crashed on the grass so no damages). Didn't even have the time to "react" pulling up the left stick.. I have been lucky because I was planning to fly over a little lake but I didn't.
2020-3-9
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JJB*
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djiuser_ot92D092RvOj Posted at 3-9 07:40
My MM yesterday dropped from 9m height to 0 in almost no time. I was just moving forward at 6m height when I noticed it was actually ascending. So i left the right stick, and right after I could see the MM going down, until it crashed on the ground (fortunately crashed on the grass so no damages). Didn't even have the time to "react" pulling up the left stick.. I have been lucky because I was planning to fly over a little lake but I didn't.

Hi,

If you like post your flightlog using this link > https://www.phantomhelp.com/LogViewer/Upload/
Curious if this is another uncontrolled descent or something else.

cheers
JJB
2020-3-9
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Guorium
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speed_freakz Posted at 1-4 10:25
I had the same problem , not sure  is it related  but your battery was 3.496v at the time when the drop occured, I had the similar readings when  my  drone  dropped , but my both  cells  were at 3.44. I was flying higher than you tho, at 40 feet.
Funny thing is that  none of my commands to pull drone up higher  were  registered  at log but I remember  holding stick  up for few seconds.

At 1:53, this is done by you?
2020-3-9
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Guorium
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fracz Posted at 1-4 09:28
Thank you JJB* for your fast diagnosis!

Does it mean that the drone positions itself based on the VPS sensor only? I always thought it has some sort of barometer for calculating its height.

To add to JJB's comment. VPS uses a downward infrared with height sensors like this one made by SHARP. Because they use near IR wave (wavelength is less than 1-2um), water hardly absorbs it. So it sees right through water as if it is not there, hence the manual says VPS does not work well over water. Landing protection also does not work so a landing mini will just go swimming unless there is a solid surface at less than 0.5m depth.

When VPS distance is working it assists altitude hold done by the barometer achieve better altitude hold accuracy. The manual quotes +-.5m for VPS assisted and +-1.5m for barometer only. Obviously this does not explain why some people lose 3m-5m according to the screen, but equally we do not know how accurate DJI stated specs are. The mini works well low over water most of the time (even when going fast), all you can do now is taking great care when doing such flight. Eyes peeled and keep your thumb on the upstick!
2020-3-9
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djiuser_NflStALHHoH7
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Hello fellow dronies,

I had a situation a few hours ago and would love to hear your opinion on the altitude drop that almost cost me my drone. It is in this video on my channel with two cams on the action (drone and a standard cam). The channel is *Wear and Tear Linz* and the video tile is:DJI Mavic Mini Almost Destroys Itself (Altitude Drop)
Sorry, can't post links it seems. The situation was:

-from the top of a cliff
-over a highly reflective surface (river)
-in a tight valley with low GPS
- I had drops only in a certain area of the flight zone
-with a fresh battery pack
-position mode

Sudden altitude drop of 2-3 meters. Very sluggish to regain altitude, little trust. More drops, imprecise handling. The drone performed as usual later in the day, including above water but with better GPS and a different battery.


2020-5-20
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fracz
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djiuser_NflStALHHoH7 Posted at 5-20 07:50
Hello fellow dronies,

I had a situation a few hours ago and would love to hear your opinion on the altitude drop that almost cost me my drone. It is in this video on my channel with two cams on the action (drone and a standard cam). The channel is *Wear and Tear Linz* and the video tile isJI Mavic Mini Almost Destroys Itself (Altitude Drop)

The link: https://youtu.be/HmvK4MlI4ZQ
2020-5-20
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wee.minidrone
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Question for the experts, let's say you want to fly low over water (river, ocean etc.).  Would it be advisable to force the drone to fly in Atti mode by covering the downward sensor? (with the understanding that the drone will behave differently, i.e. no brakes etc.).  Or is that just asking for trouble?
2020-5-20
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