DJI Mini 3 Pro | Uncontrolled sinking leads to ditch into ocean despite countermeasures

[BudWalker]

Today I received an answer from DJI regarding my flyaway case:

"Flight time: 2024-01-27 22:13:04 GMT+8

MC SN: XXXXX FLY(90) BAT SN: XXXXX



1. The aircraft worked under Sport mode after took off.

2. Flight Time T=00:40, Relative Height H=5.0m, The GPS signal was weak, affected its positioning accuracy, the aircraft came into contact with the water.

3. Please wait until the aircraft gained enough GPS signal to operate the aircraft.



As a result, it was determined that the incident was due to a non-manufacturing defect. We therefore regret to inform you that this case is not eligible for a free replacement under the warranty."


For me this isn't the answer I hoped for. I thought there would be some information about the cause that led to the ditching.
If it is really just my piloting mistake I would love the hear the specific reason to learn from this for the next time, but as far as I don't understand why the drone didn't react to my RC commands I can't believe that it's just a piloting error.
What do you guys think?

I answered the DJI mail with the specific questions about the drones missing reactions to my RC commands and why this could have happened.
Let's see

Can you try asking DJI for a copy of the .DAT they are using for their analysis? It's likely the .DAT that got synched from you device running the Fly App.

 

[matzeulrich]

Can you try asking DJI for a copy of the .DAT they are using for their analysis? It's likely the .DAT that got synched from you device running the Fly App.

Great idea!
Sure, i will try this!

Edit: File is requested

 

[rwilliam99]

As a result, it was determined that the incident was due to a non-manufacturing defect.

What is a "non manufacturing defect"? A defect is a defect - sounds like a software bug to me.

 

[matzeulrich]

What is a "non manufacturing defect"? A defect is a defect - sounds like a software bug to me.

This may be a translation fault by myself.
The original text was in German so I translated it via deepL for everyone to be able to understand. The translation is not quite accurate and should say fault or error instead of defect. Sry for this inconvenience!

Edit:
This is the original text from the mail from DJI:
"Als Ergebnis wurde festgestellt, dass der Vorfall auf einen nicht herstellungsbedingten Fehler zurückzuführen ist. Daher bedauern wir Ihnen mitteilen zu müssen, dass dieser Fall nicht für einen kostenlosen Ersatz im Rahmen der Garantie berechtigt ist."

 

[Meta4]

What is a "non manufacturing defect"? A defect is a defect - sounds like a software bug to me.

It's probable that something was lost in translation and DJI meant it's not a manufacturing defect.

 

[Frank071]

"Fehler" should, in this case, probably better be translated with 'error'. With 'einen nicht herstellungsbedingten Fehler' likely to be interpreted as 'an error that is not related to the manufacturing'.

 

[matzeulrich]

Can you try asking DJI for a copy of the .DAT they are using for their analysis? It's likely the .DAT that got synched from you device running the Fly App.

@BudWalker, do you know if DJI has the .DAT files after synching flights to their servers? the DJI support told me, I could find the .DAT files on my RC in the "MCDatFlightRecords"-Folder. Of course I had already checked this folder, but sadly it's empty. Just trying to confirm if someone already had the experience that DJI sent the .DAT file back to them?!

 

[BudWalker]

@BudWalker, do you know if DJI has the .DAT files after synching flights to their servers? the DJI support told me, I could find the .DAT files on my RC in the "MCDatFlightRecords"-Folder. Of course I had already checked this folder, but sadly it's empty. Just trying to confirm if someone already had the experience that DJI sent the .DAT file back to them?!

I recall someone having success at this. The DJI person you are communicating with may not understand that the .DAT gets removed from the MCDatFlightRecords folder when the .DAT is uploaded to DJI.

Since they have a .DAT that can not be from the AC it has to be the .DAT recorded by the Fly App.

 

[matzeulrich]

DJI says, they can't send me the .DAT file, because they don't have it, too. They "only" have the flight log, that the RC uploaded to the DJI servers. I don't know what kind of file this is, but they say, it's not the .DAT file.
And they also mentioned, the .DAT files wouldn't be deleted after synchronization of flights with the DJI server. I can't test and control what is true about this topic, as I don't have my drone anymore. But I read a lot about the topic that .DAT files would be deleted after sync with DJI servers.

This is the original message I got from them:

"If you want to export the .dat file, you can follow the steps below. Please note that DJI does not have access to the files on your side and syncing does not affect the files in your controller. Please turn on the controller and connect it to the Windows computer via USB cable. You can find the data by checking DJI RC\Internal shared storage. There are text files called DJIFlightRecord. The .dat files can be found under the MCDatFlightRecords folder."

 

[slup]

DJI says...

Think you should ask them to explain why the drone descends even though you command full ascend with the throttle & why this is an error on your side... use the chart in post #5 & the period where the chart marker is placed.

 

[matzeulrich]

Think you should ask them to explain why the drone descends even though you command full ascend with the throttle & why this is an error on your side... use the chart in post #5 & the period where the chart marker is placed.

This would have been my next step using your analysis for some more deeper questions to the tech-team.

But this morning I received an email from the DJI support team saying that the drone will now be replaced free of charge.
The reason given by the engineers is as follows:
"They [the engineers] have investigated whether there was a possibility that the drone may have had engine power saturation. Taking these considerations into account, they have decided to change the outcome to a free replacement under warranty as we truly value you as our customer."

Im very happy about the free replacement but the but the explanation for the possible crash is still not really clear to me. What can I imagine by a "engine power saturation"? Someone has an idea? I also asked this question back to DJI and wait for some more details.

Thank to all of you, assisting me in this case!!

 

[slup]

...but the explanation for the possible crash is still not really clear to me. What can I imagine by a "engine power saturation"?

That means that the motors are commanded to 100% & they follow that & reaches max RPM's... but for some reason that doesn't create the thrust needed in order to keep the drone airborne.

The reason can be as I wrote back in post #5...

"Can it be front props that are flattened & doesn't generate enough thrust..? That would explain why the drone can pitch forward with ease, but in the process not enough total thrust is generated to keep the drone airborne."

 

[matzeulrich]

That means that the motors are commanded to 100% & they follow that & reaches max RPM's... but for some reason that doesn't create the thrust needed in order to keep the drone airborne.

The reason can be as I wrote back in post #5...

"Can it be front props that are flattened & doesn't generate enough thrust..? That would explain why the drone can pitch forward with ease, but in the process not enough total thrust is generated to keep the drone airborne."

Ah right, I remember!
Sadly we can't really find out for certain what the cause has been.

For myself I can say I learned a lot through this case. Before this incident I didn't know there would be flight log files with such a lot of information. And luckily there is software to analyze the given data into understandable and visual graphs.
Here are some of my learnings I will use in the future flying my drones:

1. Always turn on screen recording when flying - it can always be the last flight
2. Don't synchronize flight data automatically with DJI, so the .DAT flight records don't get deleted and can be used for flight data analyzing, if necessary
3. Change props from time to time
4. Don't rush when flying an UAV
5. Wait for GPS lock on the aircraft
6. Fly careful when in sport mode and watch altitude data repeatedly

Anyone else want to add something to this list for all the people reading this thread afterwards?

 

[rwilliam99]

Ah right, I remember!
Sadly we can't really find out for certain what the cause has been.

For myself I can say I learned a lot through this case. Before this incident I didn't know there would be flight log files with such a lot of information. And luckily there is software to analyze the given data into understandable and visual graphs.
Here are some of my learnings I will use in the future flying my drones:

1. Always turn on screen recording when flying - it can always be the last flight
2. Don't synchronize flight data automatically with DJI, so the .DAT flight records don't get deleted and can be used for flight data analyzing, if necessary
3. Change props from time to time
4. Don't rush when flying an UAV
5. Wait for GPS lock on the aircraft
6. Fly careful when in sport mode and watch altitude data repeatedly

Anyone else want to add something to this list for all the people reading this thread afterwards?

After #5 I would add a step to confirm the orientation of the drone on the map (make sure it shows it pointing in the correct direction) - this ensures that everything got initialized correctly.
You might also add another item - immediately after takeoff, hover drone near eye level to make sure everything looks OK - it is hovering correctly, not jittery, etc and that is is responding normally to control inputs.

 

[matzeulrich]

Today I received my replacement Mini 3 Pro.
Thanks to all, who helped me!

 

[Filmarik]

Today I received my replacement Mini 3 Pro.
Thanks to all, who helped me!

Congrats to your new drone!
Along the way a "flattened props" have been mentioned a few times. Never heard of that before but this scared the hell out of me!!!! Does this mean that DJI props ( I have Mavic 3 Pro) "flatten" overtime just from flying or by ageing? I guess it means that they loose the original shape / pitch?? Is this a known issue with a specific DJI drone?? How do you measure that? When is the time to replace? After certain number of flight hours or after several months even if the props are otherwise undamaged??? I am curious to know and to find out more about this!!

 

[Yorkshire_Pud]

Does this mean that DJI props ( I have Mavic 3 Pro) "flatten" overtime just from flying or by ageing?

Not in general.
If you read some mavic mini threads you will find it was a problem caused by the way the blades of the rear motors were supposed to be stored in the hard case, they got squashed.
The propeller blades of the Mini 2 and presumably the other Mavic style drones are stiffer than the propeller blades of the Mavic Mini and not as suceptable to this kind of deformation.

 

[Filmarik]

Not in general.
If you read some mavic mini threads you will find it was a problem caused by the way the blades of the rear motors were supposed to be stored in the hard case, they got squashed.
The propeller blades of the Mini 2 and presumably the other Mavic style drones are stiffer than the propeller blades of the Mavic Mini and not as suceptable to this kind of deformation.

Thanks. That brings a bit of peace of mind. As I said, I never heard of this issue before and the mention of flattened props really shook me to the core.