Experienced pilot, but took this out yesterday to get used to flying it, did 1.8km no issues across water at 70m height, came back - tried sport mode - Mavic Mini instantly starts decending into the ocean (was about5m up)!!! just caught it before it dipped under. WTF DJI? The specific error comes up as a code 30049 "GPS signal weak" in Airdata, but also shows solid locks right through of 13-16 satelittes?! You can see on the screen recording, not sure why it says "sensor error" but Airdata shows it as a GPS signal error"?

This happened just after I switched to sport mode, but not sure if that's a conincidence. Any idea's? Other than that, signal looks like it will go well over 2000m no issues at all and the camera is dare I say... superior to my Mavic Air and Pro! But man, this sort of behaviour makes me nervous DJI!!....

sensor error

Probably too close to the water, vps got confused

But there looks like there is a software bug in sport mode that others are reporting

lannes Posted at 2-13 17:24
Probably too close to the water

Possibly, did cross my mind, have flown plenty with the Air and Pro just above the water and never an issue, this was weird and as soon as I engaged sport, was actually about 5m up despite Airdata saying 1m.

There are many reports of this issue.  Please read other threads.....If I recall there is an answer.

I believe it was to "Refresh the Firmware"  and that solves the altitude changing......Be sure to read for yourself......

Randy

rwynant V1 Posted at 2-13 17:26
There are many reports of this issue.  Please read other threads.....If I recall there is an answer.

I believe it was to "Refresh the Firmware"  and that solves the altitude changing......Be sure to read for yourself......

Cheers, did search this error extensively but didn't see a definitive answer, will certainly try refreshing the firmware and see if that makes a difference.

Please could also upload the DAT file from your mobile and share the download link in here.

grahamjohnson10 Posted at 2-13 17:48
Please could also upload the DAT file from your mobile and share the download link in here.

Will do, unlike Dji GO4 though could not figure out how to do this in Dji Fly? Can't access it either through the Dji Assistant software, just falls over, will have another go tonight, cheers

Look further down, the battery is getting below 20%, that's why it began to land.

Geebax Posted at 2-13 17:51
Look further down, the battery is getting below 20%, that's why it began to land.

Nothing about that whilst in flight however in the app, warnings etc. and it was a very sudden decent as you can see, def not battery related as it was at 27 percent when it happened.

lannes Posted at 2-13 17:24
Probably too close to the water, vps got confused

But there looks like there is a software bug in sport mode that others are reporting

Probably too close to the water, vps got confused
The question was about losing GPS.
The only way lose GPS by going too close to water, is to go under the water.

Mavic Mini instantly starts decending into the ocean (was about5m up)!!! just caught it before it dipped under. WTF DJI?
The Mini is well known to suffer from uncommanded descents.
Perhaps this was just another one.
Post data so we can get an idea of what was happening.

The specific error comes up as a code 30049 "GPS signal weak" in Airdata, but also shows solid locks right through of 13-16 satelittes?! You can see on the screen recording, not sure why it says "sensor error"
Again .. if you want to know what's ahppening, we need to see actual data.
Until data is available, all anyone can do is guess .. and most are likely ti be wrong.

Labroides Posted at 2-13 17:53
Probably too close to the water, vps got confused
The question was about losing GPS.
The only way lose GPS by going too close to water, is to go under the water.

Has me confused as well as the app says "sensor error", and Airdata says "GPS error" both different I would have thought. I guess a sensor error explains the sudden drop better than a GPS error which might just cause unstability and force into ATTI mode, which it didn't.

Labroides Posted at 2-13 18:00
Mavic Mini instantly starts decending into the ocean (was about5m up)!!! just caught it before it dipped under. WTF DJI?
The Mini is well known to suffer from uncommanded descents.
Perhaps this was just another one.

Trying to pull the data, on iOS, can't get .dat files, only txt files. Have read the .dat files are no longer available / readable on Dji Fly app? Thanks, will keep trying.

Can't access the .dat files at all, blank folder due to this we gem I discovered....

"The DJI Fly app appears to delete the DAT files if and when it syncs flight records with the DJI servers, and so they are often missing from the MCDatFlightRecords folder.​"

Thanks for nothing Dji!!!

TroutboyNZ Posted at 2-13 18:01
Trying to pull the data, on iOS, can't get .dat files, only txt files. Have read the .dat files are no longer available / readable on Dji Fly app? Thanks, will keep trying.

The .txt file is all I need, forget the .dat file.

TroutboyNZ Posted at 2-13 18:00
Has me confused as well as the app says "sensor error", and Airdata says "GPS error" both different I would have thought. I guess a sensor error explains the sudden drop better than a GPS error which might just cause unstability and force into ATTI mode, which it didn't.

Has me confused as well as the app says "sensor error", and Airdata says "GPS error"
Your drone has a number of different sensors.
The GPS receiver is just one of them.
Get the real data and we can see what really happened instead of Airdata's translation which can sometimes be misleading.

https://www.phantomhelp.com/LogViewer/GWIDDPQZB7C3CFBQX4ZH

Doesn't show much at all, happens around 17:38 is the sudden drop? There is a "GPS Position NoMatch" error around the same time that corresponds with the falling though?

TroutboyNZ Posted at 2-13 18:48
https://www.phantomhelp.com/LogViewer/GWIDDPQZB7C3CFBQX4ZH

Doesn't show much at all, happens around 17:38 is the sudden drop? There is a "GPS Position NoMatch" error around the same time that corresponds with the falling though?

Before 17:38.1 the drone is holding altitude in hover but from 17:38.1 it starts to descend.
At 17:39.4 it has lost 9 feet of altitude and you give it full left stick up (Sport Mode) for 1.5 seconds.
The drone is very sluggish to respond and sinks further before gaining 5.6ft and then sinking again.
1.8 seconds of left stick from 17:42 gets the drone back up and it appears to recover and is again able to hold altitude for a while but by 18:54.9 it's sinking again.briefly and recovers again.

You had no problem at all with GPS (Airdata is giving you a false alarm).
The GPS Position NoMAtch message is a common false alarm that is meaningless.
The flight controller showed that it had full confisence in GPS the whole time.

GPS had nothing to do with the issue but you have the same uncommanded descent problem that has caused the loss of several Minis.

It was only minor in this flight but most I see are terminal and never recover.

Labroides Posted at 2-13 19:05
Before 17:38.1 the drone is holding altitude in hover but from 17:38.1 it starts to descend.
At 17:39.4 it has lost 9 feet of altitude and you give it full left stick up (Sport Mode) for 1.5 seconds.
The drone is very sluggish to respond and sinks further before gaining 5.6ft and then sinking again.

Thank you, kinda my thoughts as well and unfortunately nothing i can do about it, was just lucky I was fast on the sticks as what you state is exactly what happened or it would have gone in the water. I hope they can rectify this...

TroutboyNZ Posted at 2-13 18:04
Can't access the .dat files at all, blank folder due to this we gem I discovered....

"The DJI Fly app appears to delete the DAT files if and when it syncs flight records with the DJI servers, and so they are often missing from the MCDatFlightRecords folder.​"

I wrote the post on this forum warning users to disable the autosync in DJI Fly to prevent loss of their DAT files.

TroutboyNZ Posted at 2-13 19:07
Thank you, kinda my thoughts as well and unfortunately nothing i can do about it, was just lucky I was fast on the sticks as what you state is exactly what happened or it would have gone in the water. I hope they can rectify this...

Do you happen to know Wind direction and Wind speed along coast your first flew up, turned 180, flew back down?
Coast appears to be East & West, with Bay to North.

TroutboyNZ Posted at 2-13 19:07
Thank you, kinda my thoughts as well and unfortunately nothing i can do about it, was just lucky I was fast on the sticks as what you state is exactly what happened or it would have gone in the water. I hope they can rectify this...

was just lucky I was fast on the sticks as what you state is exactly what happened

You had a lucky escape with a tiny incident.
I've seen too many where no amount of stickwork makes any difference to the descent.

HedgeTrimmer Posted at 2-13 19:25
Do you happen to know Wind direction and Wind speed along coast your first flew up, turned 180, flew back down?
Coast appears to be East & West, with Bay to North.

The wind makes no difference to holding altitude for a drone that's working properly.
A mini with the uncommanded descent problem, just descends whether there's wind or it's calm.

Labroides Posted at 2-13 19:33
The wind makes no difference to holding altitude for a drone that's working properly.
A mini with the uncommanded descent problem, just descends whether there's wind or it's calm.

After seeing a video posted where a Mavic Mini was having descent problems going into wind, and almost no problem going with wind; seems worth asking.

Wind was from the north at about 14kmh average, so not bad conditions at all. Had no issues all the way out to 1800m there and back, this error occurred just playing round close to me. See link.

https://app.airdata.com/share/XTWZmi/GENERALOverview

TroutboyNZ Posted at 2-13 20:07
Wind was from the north at about 14kmh average, so not bad conditions at all. Had no issues all the way out to 1800m there and back, this error occurred just playing round close to me. See link.

https://app.airdata.com/share/XTWZmi/GENERALOverview

Screen-snaps from app.airdata link:

Overview

Zoom

Appears MM was flying into wind going up coast (away from takeoff spot) and flying with wind going down coast (towards takeoff spot).
Similar to other video of MM having height drops.

One possibility...

Going into wind, MM's barometer senses higher pressure, making drone think it is flying close to ground.  Drone rises.  With pilot compensating to stay lower.
Pilot commands drone to do a 180.

Now, going with wind, MM's barometer senses lower pressure, making drone think it is flying higher above ground.  Drone lowers.  Forcing pilot to comensate to go higher.

Perhaps, JJB's FRAP2 could help by plotting baro sensor input, drone direction & speed, and pitch of drone - coming and going?

Don't use Sport mode is my Opinion

HedgeTrimmer Posted at 2-13 20:56
Screen-snaps from app.airdata link:

[view_image]

One possibility...
Going into wind, MM's barometer senses higher pressure, making drone think it is flying close to ground.  Drone rises.  With pilot compensating to stay lower.
Pilot commands drone to do a 180.
Now, going with wind, MM's barometer senses lower pressure, making drone think it is flying higher above ground.  Drone lowers.  Forcing pilot to comensate to go higher.

That scenario is a fantasy ... rather than a possibility.
It's not how the sensors work.

The air pressure doesn't significantly change because the drone turns around.

If it was that simple, anyone getting their drone into an uncommanded descent could just give it some left stick.
But dozens of incidents show that the drone keeps sinking even with full left stick.

HedgeTrimmer Posted at 2-13 20:56
Screen-snaps from app.airdata link:

[view_image]

Hi

What i see in this log is the same as in other logs where drop in height are seen.

Well, just my opinion, see the chart for details.

AFAIK and see in all the logs ; it 'always ' happens when:
- flying forward with some speed (100% fwd stick)
- fwd stick rapid to 0%.
- drone pitches from down angle to up angle [ minus 19.5 to plus 27.7 to reduce speed from 8 m/s to 0 m/s ]
- because of this drone climbs a little ( FC to slow in correction the vertical lift component)
- beacuse of the climb FC corrects to lower, but this is done too much and too fast
- dropping height wich is corrected again.

In my opinion the FC of the MM reacts to slow on this, my MA does this 10x better than my own MM.

This case does not look like the larger height droppings, these have something to do (i think) with battery power, mayby use of not updated battery to the latest fw.

Getting GPSnonmatch in the log beacuse of the error "GPS signal weak. Positioning accuracy affected. Fly with caution", guess due to reflecting signals due to flying low over water.

So for me and my MM, this habbit of my MM is good to know, normal flights (at some height) no problem ofcourse ; flying low over water just be carefull with speed changes.

PS A forcelanding in the log!  flying low at autolanding protection height and with 100% stick down > into autolanding! with 100% up this was cancelled.
Or it was intented i do not know, it was not above water.

cheers
JJB

Looks shockingly similar to my incident, the way it yawed and then dropped like a stone. Unlike yours, mine happened at high altitude and I was in S mode the whole time. I shall have to do some study on your log. Thanks for posting.

Labroides Posted at 2-13 23:28
One possibility...
Going into wind, MM's barometer senses higher pressure, making drone think it is flying close to ground.  Drone rises.  With pilot compensating to stay lower.
Pilot commands drone to do a 180.

He made a mistake, going against wind makes air pressure go down. With wind, the pressure goes up. "Venturi effect" describes fluid pressure to be inversely proportional to fluid speed. Do you have data to show that pressure differential due to airflow around the mini isn't significant to cause loss of height?

Guorium Posted at 2-14 04:14
He made a mistake, going against wind makes air pressure go down. With wind, the pressure goes up. "Venturi effect" describes fluid pressure to be inversely proportional to fluid speed. Do you have data to show that pressure differential due to airflow around the mini isn't significant to cause loss of height?

He made a mistake, going against wind makes air pressure go down. With wind, the pressure goes up.
That's just pseudo-scientific nonsense.
Think about it ... how is it that other drones  and most Mavic Minis don't have this problem?

And if that doesn't convince you ...
If you usually fly forwards, the horizontal airflow across the drone will be from the front regardless of the drone's orientation to any wind.
And the airflow around the drone is mostly downwards regardless of the direction of flight relative to the wind.

Hello and good day TroutboyNZ. I am sorry to know what happened to your previous flight with your DJI Mavic Mini. Kindly please update the firmware of the said drone via the DJI Assistant 2, then reboot aircraft. After this process please try to calibrate IMU and gimbal as well to see if the issue will still persist. Thank you.

Labroides Posted at 2-14 04:47
He made a mistake, going against wind makes air pressure go down. With wind, the pressure goes up.
That's just pseudo-scientific nonsense.
Think about it ... how is it that other drones  and most Mavic Minis don't have this problem?

Ok, so you have no data. Guessing it is. You can say people misuse scientific principles but cannot simply discredit the dead experts in fluid dynamics if that is what you implied. That aside, not every mini user is on forums and among those who use the forum, not all would care about a drop like that. Even among those who use forums and see a drop like that may not choose to come and report it. Although I personally find the majority of the mini community to be quite the "happy go lucky" type, it is only a matter of time until a number of reports show up. No reporting does not mean no problem.

The barometer is inside the fuselage. Shielded from outside airflow.  The down thrust of the props would not even make it into the fuselage. Any outside airflow due to either the environment or mini's own movement should be considered as wind relative to the drone. The inside pressure sensed by the barometer should equalise with outside pressure by air exchange through the vents and gaps in the fuselage. It does not care about what wind direction is on the outside, only the pressure which is determined by the relative airspeed outside. The point you were opposing was simply stating that any fast directional flow outside of the mini would cause significant pressure deviation. I myself is testing this today on a field and I know a couple of people are testing it soon. Before the testing is done, everyone is just guessing.

Also. Show me the posts where stickwork never saved the minis? I want to investigate those in my spare time.

Guorium Posted at 2-14 14:04
Ok, so you have no data. Guessing it is. You can say people misuse scientific principles but cannot simply discredit the dead experts in fluid dynamics if that is what you implied. That aside, not every mini user is on forums and among those who use the forum, not all would care about a drop like that. Even among those who use forums and see a drop like that may not choose to come and report it. Although I personally find the majority of the mini community to be quite the "happy go lucky" type, it is only a matter of time until a number of reports show up. No reporting does not mean no problem.

The barometer is inside the fuselage. Shielded from outside airflow.  The down thrust of the props would not even make it into the fuselage. Any outside airflow due to either the environment or mini's own movement should be considered as wind relative to the drone. The inside pressure sensed by the barometer should equalise with outside pressure by air exchange through the vents and gaps in the fuselage. It does not care about what wind direction is on the outside, only the pressure which is determined by the relative airspeed outside. The point you were opposing was simply stating that any fast directional flow outside of the mini would cause significant pressure deviation. I myself is testing this today on a field and I know a couple of people are testing it soon. Before the testing is done, everyone is just guessing.

I myself is testing this today on a field and I know a couple of people  are testing it soon. Before the testing is done, everyone is just  guessing.
I've been testing for 6 years and never seen the effect you are guessing might be a problem.
So have thousands of other drone flyers.
If it was a real issue, we might be able to fly our drones out, but how would we ever get them back?

Show me the posts where stickwork never saved the minis? I want to investigate those.
Here is just one of many that I've seen:
https://www.phantomhelp.com/LogViewer/1IPRYBXDWTJHW0H3IQ6V/
Jump to 4:16 and you see the drone sinking with full forward on the left stick making no difference.

There are plenty of other examples out there.
Just search for "uncommanded descent"

Labroides Posted at 2-14 14:22
I myself is testing this today on a field and I know a couple of people  are testing it soon. Before the testing is done, everyone is just  guessing.
I've been testing for 6 years and never seen the effect you are guessing might be a problem.
So have thousands of other drone flyers.

Thanks. Will take a look at that flight. I dug up my old tests on Jan 16. Full speed forward in S mode does show slight elavation and so does P mode. The mini attempts to correct itself by lowering after the stick is released. This happened in forward and backward flights. Test was conducted 2m over a pond about .5m deep. This does fit the bill for the pressure change theory.

Testing done by another forum member,  Uncontrolled descent BUG incident isolated

"after a fast manual return towards the homepoint, from full stick down  and full speed in Sport mode to a halt. Heigh discrepancy takes place  after the AC has halted and the uncontrolled descent begins. Only full  stick up can recover but quite slowly compared to how prompt the AC  usually is."

"The timing and CS inputs are clearly recorded, what I don't believe is  accurately stored is the height data which I reckon is what confuses the  FC regardless of what is being reported by the IMU sensors."

"Full CSI up causes a lethargic response because the AC is affected by some wrong logics or data."

Reading OP's description of what he did and results; reminds me of processing order problem of input commands and processing of incoming flight / sensor data.
Mavic Mini, gets behind in processing user's joystick commands, while processing incoming flight / sensor data.  The sudden halt overwhelms MM's CPU with flight / sensor data to be processed.  As a result, Mavic Mini continues to process Down joystick commands, before getting to processing UP joystick commands.

If there is a delay in processing input commands as result of processing incoming flight / sensor data, highly likely Flight Log Data is being delayed, meaning entry information does not align with actual events.

Being number of pilots reporting problem, and several people being able to replicate problem - DJI should be able too.

Guorium Posted at 2-14 16:25
Thanks. Will take a look at that flight. I dug up my old tests on Jan 16. Full speed forward in S mode does show slight elavation and so does P mode. The mini attempts to correct itself by lowering after the stick is released. This happened in forward and backward flights. Test was conducted 2m over a pond about .5m deep. This does fit the bill for the pressure change theory. [view_image]

[view_image]

This does fit the bill for the pressure change theory.
No

Labroides Posted at 2-14 17:13
This does fit the bill for the pressure change theory.
No

Then the burden of proof is on you mate. A 'NO' is hardly any proof.

BTW I analyzed that flight where up stick did not work. True it did not work. That case coincided with exiting RTH. Don't you think that may have something to do with it? Don't you also think the fact that the up stick command did not work makes it a separate issue? Up stick worked for me and TroutboyNZ. I do not know what from those cases you mentioned nullifies the pressure deviation theory. As far as I am concerned their causes might be very different from ours, therefore they have a different problem. If you group a bunch of uncommanded descend cases caused by different factors you will never find a focus to isolate the causes. We try to isolate pressure deviation here as one of the causes. We know there are other possible causes such as battery fw mismatch or loss of GPS signal.

I analyzed your flight with FRAP. I have the same conclusion as JJB. Your incident like mine was probably a result of mavic mini doing this altitude correction too fast after fast forward flight. My additional comment is, yours is the only one I have seen that resembles my incident and both were ~5m over water that renders VPS ALT useless. I think the confused VPS may have something to do with the overly fast altitude correction as I observed a much more gradual descent rate when over land. DJI has some homework to do on the FW. In the main time, we should be very careful when low above water.


You could also file a case with DJI and let them analyze your log. They did that to mine and concluded that the barometer needs checking. Offered a free repair. I haven't taken that offer up. The barometer is fine according to the log.