Almost had a fly away with my Mini

Just360 · Jun 2, 2020

Hey guys,

Still shaking after this experience. Analised the flight replay on the app to review.

What happened - I just flew up and then a little lower to capture a shot. Suddenly drone went to the side very quickly. I stopped descend and tried to get it back without realization drone rotated and I was flygint it backwards away from me (I realised second part was my fault only after flight replay review). I literally ran after my drone to avoid signal loss, as I thought I didnt get back the control yet, while I already had the control (it seems)

I'm about to get the flight log out shortly. I hope someone will help to analyse it, because im scared to fly now, honestly.

Just360 · Jun 2, 2020

was not able to get anything out with airdata.com, but here is the log

Edit: Added DAT file here, while it was added in later post (for convenience)

Just360 · Jun 2, 2020

I noticed a new folder in my flightslog folder called "MCDatFlightRecords" and it has something created at the same time as my last flight log. Never noticed this before. Is it something important? It has DAT file there.

Just360 · Jun 2, 2020

I also attach the screenrecording from reply. I highlighted that part where drone rotates and flies to the side, and then you can see me disorientated trying to fly back while drone was already rotated to different direction. No errors, nothing I can see. If not the the stick position, I would have thought my hands got crazy and I did it myself.

Couldnt upload video here, so added to youtube:

sar104 · Jun 2, 2020

Just360 said:
I noticed a new folder in my flightslog folder called "MCDatFlightRecords" and it has something created at the same time as my last flight log. Never noticed this before. Is it something important? It has DAT file there.

Yes - post the DAT file from that folder.

Just360 · Jun 2, 2020

sar104 said:
Yes - post the DAT file from that folder.

Here you go

But why I have DAT file on for my last flight and no other?

Just360 · Jun 2, 2020

Ive also analysed my log here DJI Flight Log Viewer - PhantomHelp.com and I see in visualisation that I pull my left joystick back much later in the flyaway process - what I see here matches my reaction better - I thought that find is blowing away my drone (I tried to descend the aircraft), that does not make any sense, because I checked UAV report before the flight and it was really (I say really, but of course how can I know for sure) no way there would be a gust of such strength to pull my drone away with such speed. Actually now I recall that I noticed that somethings is wrong from the picture on the screen - it was slowly moving to the side (which is a symptom of a strong wind, but I it does not match with UAV report and feeling outside). And only later I noticed my drone is flying away, so I pulled right stick down trying to get it back

Edited

RichR · Jun 3, 2020

Just360 said:
Here you go

But why I have DAT file on for my last flight and no other?

If you haven't disabled auto sync, they get uploaded to DJI and deleted from your device.

Just360 · Jun 3, 2020

RichR said:
If you haven't disabled auto sync, they get uploaded to DJI and deleted from your device.

ah got it, thanks. Will disable auto upload then - useful to have those DAT files, obviously

slup · Jun 3, 2020

Hmm ... this one looks strange ?

If we first look at the very beginning of the log, before take off. As seen where data is started to record at -39,5sec it's already a disagreement between IMUYaw & magYaw on approx 10 degrees ... that's odd as they should be initialized to the same value at power on. This make me think that the AC is powered on in a magnetic disturbed area before the DJI Fly app is started & not in the same place as the data starts to be recorded. After this the AC looks to be carried to a launch spot ... & here at -0,3sec the disagreement is now nearly 70 degrees.

So the stage seems to be set for a fly away due to this disagreement as the AC doesn't know it's heading direction.

Then we jump forward to just after take off ... it's now a disagreement between IMU yaw & magYaw on 78 degrees at 3,2sec. Then suddenly there, the IMU Yaw (light blue) correct itself to the magYaw (yellow) ... this without the VIO yaw or the gyro register any movement at all.

Then on top height the speed (green) picks up, this with no stick inputs at all ... until here it's been only throttle inputs & some very short rudder inputs. The speed is probably a wind drift which the AC soon there after try to correct. At 30sec the IMUYaw again move without being registered by VIO or gyro ... again the disagreement is 70 degrees and the heading speed rapidly rises & the fly away starts.

After this you luckily regain control of the AC (perhaps due to that the disagreement isn't up to around 180 degrees) & can fly it back ... from the moment where you gained control the disagreement between IMUYaw & magYaw was between 50-70 degrees ... and all direction changes was recorded approx equal by all sensors.

@sar104 ... can you explain this fully, it looks really odd & the magmod is really jumping up & down ... is it again the AC itself that is magnetized?

Just360 · Jun 3, 2020

wow, that super interesting. Thanks a lot for such a detailed look into it.

If its any help - I did fly in this same place few times in past two weeks. It has very small amount of wifi spots and I had very good signal every time until this flight above.

slup · Jun 3, 2020

Just360 said:
wow, that super interesting. Thanks a lot for such a detailed look into it.

If its any help - I did fly in this same place few times in past two weeks. It has very small amount of wifi spots and I had very good signal every time until this flight above.

Can you describe how & where you powered on all equipment before take off ...

-Did you power on the Mini before the DJI FLYapp or remote was running?
-Where did you power on the Mini ... was it somewhere else than the launch spot?
-Was the Mini pointing in the direction shown below just before take off?

Just360 · Jun 3, 2020

slup said:
Can you describe how & where you powered on all equipment before take off ...

Sure,

1. connected iphone to the remote
2. switched on the remote
3. insterted battery into aircraft swithced it on
4. walked few feet to the side further from the small trees nearby - Yes, aircraft was pointing that direction, as I was targeting the sunset.
5. waited until got GPS locked (at this point I think I was already standing at my launch point for quite some time)
6. used automated lift off from my hand (high grass in the area, wanted to avoid debris etc)
7. I was going up without flying to any direction (I remember home point is locked down properly only after 30meters ascend, someone told me, so I always lift up straight to reasonable heights (more then 30 meters) before flying to any direction.

Did I answer all your questions fully?

slup · Jun 3, 2020

So the remote AND DJI FLYapp was up & running before the Mini was powered on ... & you held the Mini horizontally (feet down)?

Did you power on the Mini near something magnetic, (or even in house & then stepped outside?) ... or if you had it in your hand the whole time, any (smart)-watches, bracelets or rings on that hand?

Just360 · Jun 3, 2020

slup said:
So the remote AND DJI FLYapp was up & running before the Mini was powered on ... & you held the Mini horizontally (feet down)?

Did you power on the Mini near something magnetic, (or even in house & then stepped outside?) ... or if you had it in your hand the whole time, any (smart)-watches, bracelets or rings on that hand?

Yes, app and remote was on before I turned on the Mini. It might be that Mini was at the angle at the moment of switching it on, but immediately afterwards I held it horizontally. Otherwise you get get sensor errors on the screen, as I remember - so I always keep it horizontally immediately after powering Mini on.

Nothing magnetic near. I was near the house, and even that house is wooden 100 year old house.

I might have had my apple watch on me. I say "might", because I had it absolutely always on during my previous 150+ flights, but recently I have it on only on rare occasions. I will not say for sure, but even if I had it, that would be usual process I launch the drone.
I held it in my hand all the time, in the right hand, on which I never wear a watch or apple watch and I also have no rings on that hand.

slup · Jun 3, 2020

OK ... so it's still a mystery why you end up with a disagreement between IMUYaw & magYaw up to 70 degrees ... that's enough to cause what you experienced. And it's also a mystery why the IMUYaw un-noted by all other sensors turns to align with magYaw for a short period & then goes back to disagree with 70 degrees.

As the forums wisest ( @sar104 ) tried to teach me not long ago ... it can also be that something on the Mini itself have been magnetized ... either some gadget attached to the drone or that it have been stored near some magnetic (standing on top of a loud speaker, or in a trunk of a car for instance). If we look at the magnetic field during the flight (magMod) it changes dramatically ... in line with how the Mini pitches, this can if I understood sar104 correctly indicate just that. But again it doesn't explain the IMUYaw movement ... think we have to wait for sar104 to chime in & give us som clarity

Just360 · Jun 3, 2020

slup said:
OK ... so it's still a mystery why you end up with a disagreement between IMUYaw & magYaw up to 70 degrees

Very intersting. Thanks for for all the effort trying to understand reason of this issue.

I stored my Mini in combo case, in back pack in the same place I did store it before other flights. Only close thing that I would consider magnetic (I think I would be wrong), is a fridge, which was about 1 meter away from my backpack. Nothing else I could consider magnetic. Also I had no attachments on my mini (I sometimes use lens cover to protect from lens flare or/and ND filter, but nothing was attached this time)

Just360 · Jun 3, 2020

I noticed one thing while viewing replay in DJI FLY app. While direction is correct in @slup screenshot above, replay shows not the same direction. it seems about 70 degrees to the left in replay, while it was straight A.Varno Gatve (can see in the map)

slup · Jun 3, 2020

Just360 said:
I noticed one thing while viewing replay in DJI FLY app. While direction is correct in @slup screenshot above, replay shows not the same direction. it seems about 70 degrees to the left in replay, while it was straight A.Varno Gatve (can see in the map)

You can see the Yaw disagreement between the IMU & the compass graphically below ... the position is just when you take off & the green bar is the IMU direction & the blue bar is the compass direction. The difference is approx 70 degrees there and mean that the Flight controller doesn't have knowledge about in which direction the Mini is pointing.

When a drone in this state are affected by external factors, wind for instance ... it tries to hold position by giving counter thrust to come back to the correct position. If the drone isn't turned in the way the FC thinks it will apply thrust with the wrong motors ... leading to that the position error just becomes larger ... & the FC tries again & again and fail each time. All this happens in lightning speed ... and the drone "fly away" in a very distinct "bathtub or toilet bowl curved" flight path. This effect is usually more severe when the disagreement is around 180 degrees ... the "only" 70 degrees you had was what possibly saved you.

*EDIT*

I can add one easy check to discover issues like this before you take off & need to experience a "fly away" due to a yaw error.

Always power on the AC well away from magnetic interference. Once on, check that the drone icon on the map in the DJI FLYapp is pointing equal to reality in relation to objects on the map ... roads, houses for instance. If the icon on map & the drone in reality isn't pointing equal ... power down move away to another spot & power up again & check ...

Just360 · Jun 3, 2020

slup said:
... it tries to hold position by giving counter thrust to come back to the correct position. If the drone isn't turned in the way the FC thinks it will apply thrust with the wrong motors ... leading to that the position error just becomes larger ... & the FC tries again & again and fail each time. All this happens in lightning speed ... and the drone "fly away" in a very distinct "bathtub curved" flight path. This effect is usually more severe when the disagreement is around 180 degrees ... the "only" 70 degrees you had was possibly what saved you.

oh, now it makes total sense to me. Thanks for this extra explanation