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Strange Flight

SJGMoney

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So I took my Mavic Mini out for a lunch flight and was about 1:30 into the flight when my bird rotated 90 degrees and seemed to yaw to the right totally out of the blue. Hopefully you can see this U-turn in the picture attached, only stick inputs were forward thrust yet it rotated at least 90 degrees and seemed to change position strangely. Unfortunately I wasn't recording video at the time, but watching thru my phone was enough to get the blood pumping fast. Attached is the log, wondering if you guys see anything strange. Flew back and then continued to fly in the same general area for another 15 minutes or so with no issues so doubt it was a mechanical issue. Bumped by a bird, sudden gust of wind? In the picture attached you can see it looks like I was trying to draw a heart or something, that's when it changed course all of a sudden.

No crash or disaster but I appreciate your input.

 

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eEridani

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Looks like compass errors and high interference at the aircraft, plus an LOS midflight.
 

SJGMoney

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Looks like compass errors and high interference at the aircraft, plus an LOS midflight.
No LOS before that event at 1:30. Any interference and LOS warnings came much later (and further away) than that point in the flight. Compass error occurred after I landed.
 
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eEridani

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No LOS before that even at 1:30. Any interference and LOS warnings came much later (and further away) than that point in the flight. Compass error occurred after I landed.
I just did a quick survey of the data. I haven't dug into the CSV or looked line by line for heading data, so this is just an educated guess. That turn is after you let off the throttle and restarted, causing normal pitch changes. As pitch and roll change, compass errors can magnify themselves. The fact an error was flagged at the end of the flight hints it was probably there at the beginning of the flight, too. Notice that as you headed the other direction, you have two uncommanded left hand turns that are probably from the same cause. And if you look closely at every place you stopped, the drone did some small but odd turns.

Add the interference problem. There is an interference report at the location the drone did the uncommanded turn. Interference was probably present the entire flight. The drone was having a hard time hearing the controller.

ps: someone will probably come along say I am wrong and tell you something different, but I'd check the drone compass cal.
 

slup

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Most likely this had nothing to do with either a loss of connection, signal interference or any compass error coming in the end of the flight ... nothing in the .TXT log or how a Mini usually behaves gives anything pointing in that direction.


This requires the mobile device DAT log ... the one for this flight ends with FLY048.DAT & it's located where you found the .TXT log but in a sub folder MCDatFlightRecords. Retrieve it & attach it in a new post here ...

The uncommanded yaw movement is clearly seen at approx 90sec where I've placed the chart marker. The blue yaw degrees change rapidly without any green rudder input.

1644260698496.png

Interestingly we also find big velocity deviations between the GPS & IMU starting off just at that same moment ... this usually indicate IMU problems.

1644260886227.png
 

SJGMoney

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Hmmm...my McDatflightrecords folder is empty. Pretty sure I'm looking in the right place:

This PC\Pixel 4a (5G)\Internal shared storage\Android\data\dji.go.v5\files\FlightRecord\MCDatFlightRecords
 

Paint Rock Drones

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How are you looking at the folder? On my Pixel 4a the built-in files app could not see the files in that folder. I had to connect by USB to my (Windows) computer, and then I could see the files.
 

slup

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Looks like because I have my flight records auto sync they are erased from the phone. So...where in the cloud are they? I assume some DJI site, correct? @slup
OK ... that's most probably why it's emty.

We have one other possibility as it's a Mavic Mini 1 ...

The Mavic Mini 1 maintains the most recent DAT file named fc_log.log on the removable SD card in hidden folder: MISC » LOG » flylog.

Check if you can find that one ...
 

slup

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Do you have any cloud storage you can use ... Dropbox, & then share the link.
 

slup

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See if this works...
Yeah, it works ... but sadly you continued to fly after the incident & that made the flight of interest to be deleted & replaced by others.

This was the flight where the incident happened at the red cross ...

1644270386149.png

And below was the 2 flights in the fc_log.log


Another at the same incident location...

1644270445396.png

... and a second a bit north east of the incident location.

1644270545115.png

So ... we will not be able to get hold of the raw sensor data to determine what exactly failed.

But looking at the velocity deviation between the GPS & IMU ... which peaked up to nearly 18mph in an easterly direction ... and then also looking at the IMU heading speed (black graph below), which went higher than the maximum specified speed of a Mini 1 + the jagged look of the graph... I guess this was a IMU failure which momentarily caused a yaw error. Can't say anything about if it's of permanent nature or just a computational error, unfortunately.

As seen below the black heading speed goes nearly to 29mph while the dashed blue indicate that your stick was in neutral (value 1024).

1644270854381.png
 

SJGMoney

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Yep, I continued that flight after getting it closer to home point and having no other issues (didn't start a new one). And the only issues I had after that crazy one was just normal signal interference, weakening controller signal due to distance etc. Those other flights you posted were on different days.

Stupid question: I've calibrated the IMU before when I got the message on the screen and had to, but is there a way to do it again even though I'm getting the normal, ready for flight message?
 
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slup

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... I've calibrated the IMU before when I got the message on the screen and had to, but is there a way to do it again even though I'm getting the normal, ready for flight message?
Settings in the FLY app (3 dots upper right corner) ... then

1644273459462.png
 

eEridani

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And you may want to read this:
 
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SJGMoney

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Interesting read. The place where I launch from work is the top (3rd floor) of a parking garage. Unlike when I fly at home or other places I get a "Need compass calibration" warning EVERY time I fly. So i calibrate the compass (as I did yesterday preflight). (no IMU calibration warning ever though). The garage seems to me to be mostly concrete although I'm sure there is steel involved, however it has a strange material for a floor, almost a coating of some sort, not straight concrete or asphalt. I'm wondering if it has some metallic material in it that causes issues and forces me to calibrate every pre-flight.

I still don't know what to make of yesterday's issues because the rest of the flight was normal and I flew in that same direction much further later in the flight.
 

slup

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...I still don't know what to make of yesterday's issues because the rest of the flight was normal and I flew in that same direction much further later in the flight.
Even though the linked article about the compass is interesting reading & a good learning ...

A yaw error coming from a magnetically disturbed compass at power on of the craft, had nothing to do with what happened in the incident flight.

If it had been a disturbed compass that initialized the IMU at power on ... the IMU have had wrong information about the true heading of the drone already from start (which we don't see in the log, it's correct there) ... this had caused it to fly away in a uncontrollable way very early in the flight... as soon as it tried to hold position against the wind for instance.

Once the compass have initialized the IMU it's the IMU that handles the flight ... both the compass & the gyro act as secondary equipment where they slowly feed in corrections to the IMU heading direction ... that's why a drone doesn't immediately develops a yaw error if you fly close enough to a steel structure which deflects the compass.

So no ... it's very unlikely that the compass had something to do with that shorter instance between 88-110sec into the flight.

The 2 compass errors you got just in the end of the flight when it was landing most probably came from that the location where you landed was enough distorted so the magnetic field strength went over the threshold value.
 

eEridani

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Pretty sure a compass problem will cause yaw errors when the drone pitches. The drone yawed abnormally every time it stopped, and the yaw was directional. Right headed west, left headed east. May also be an uncalibrated gyro in the IMU, but that would typically be unidirectional, not based on compass.
 

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