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Near flyaway IMU error w/logs and video
412 4 2018-4-23
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jetto black
lvl.4
Flight distance : 202995 ft
United States
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Video + screen recording:    (problem starts around 0:53)

Log: http://www.phantomhelp.com/logviewer/KYA5GRIRFA3VFH2I06RA/   (errors start around 8m 4.3s)

* Spark w/latest firmware and latest DJI Go4 app for iOS
* Using WiFi (not OTG)
* I've never calibrated the compass or IMU because I've never been prompted to (following advice in this forum)
* 15-19 sats locked all the time, clear day with low solar activity
* Took off from a grassy field with no metal nearby (no power lines, no rebar, no tall structures, etc.)
* Home point recorded & verified that compass was showing the correct direction
* Completed one flight with no problems on the first battery
* Repeat the above for second flight on the next battery
* While manually flying home, "IMU Exception" "Speed Error" "Compass Error" "Yaw Error" switching back and forth between Atti and GPS mode
* Despite virtually no wind (< 5 mph at current altitude), drone began RAPIDLY drifting in random directions
* I was fighting the controls, although for some reason it doesn't really show up in the screen recording (for example, the left stick shows ascending/descending but not yaw movements)
* Fortunately, I was able to maintain control, narrowly avoided some trees, and got it back unharmed.
* Had the signal been any weaker, I'm certain this would have been a flyaway.

Question: Is there any point in sending this Spark back for service?

Was there anything else I could have done to prevent this?

Thanks.


2018-4-23
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DJI Elektra
Administrator
China
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Hi, did you try to calibrate the IMU after this error? I would recommend you ensure that there is no interference around your spark. Please try to test again in an open field without interference. You can fly in beginner mode and see if you get the same result. If the problem remains, please export the flight data and the black box for analysis. You can upload it to dropbox and post the link here. Thanks for your support.

2018-4-23
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Flighty
Captain
Flight distance : 1917969 ft
Croatia
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Forum information on not calibrating the IMU or compass is correct, however I had a similar experience you mention and when I finally got the Drone back down I immediately re-calibrated the IMU and got back up flying with no further issues. (Not easy bringing the bird back under those circumstances,, good flying)
2018-4-23
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Jakab Gipsz
First Officer

Hungary
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Please describe the event briefly in:
https://forum.dji.com/thread-151287-1-1.html
The goal is to find the similarities and to infer the cause of the mistake.

Thanks. G. J.
2018-6-5
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Mirek6
First Officer
Flight distance : 372986 ft
Canada
Online

Hey Jetto Black,

You said - "I never calibrated compass or IMU because I was never prompted (following advice on this forum).
Yes - frequent and unnecessary calibration may do more damage than help, especially if there is no reason for calibration. However, I would always advise new drone owners to calibrate compass and IMU before they fly it for the first time. Compass and IMU is calibrated in factory back in China, but if you fly on the other side of the world, magnetic declination in your place versus place of origin may be significant. This is why the forum also advises to calibrate compass when you move large distances between flights (several hundred kilometres).
Also, calibration of IMU may have gotten skewed in transport.

Having said that, and seeing what you went through, I believe that DJI software did not respond correctly to uncalibrated Compass and/or IMU and should have given you a warning. So no error on your part but just missed precautions.

Behaviour of your Spark is consistent with compass and/or IMU errors and/or, perhaps, losing satellite connection. Spark relies on ideal sync between what compass says and what IMU says. It also relies on GPS co-ordinates and compares all three together. If something is inconsistent, Spark switches to ATTI mode to avoid trouble since it cannot reconcile conflicting data. If it drops to ATTI and stays there, situation is not bad - you can fly manually. If it starts rapidly switching between GPS and ATTI for whatever reason, you are in trouble. As soon as it gets to GPS mode, it may recalculate its position and figure that it should be adjusted - so it moves. While moving it figures that compass is wrong so it drops to ATTI again. Than, for whatever reason figures all is OK and switches to GPS and the dance begins. Google "toilet bowl effect" so you will understand what I am talking about. Spark avoids toilet bowl effect by switching to ATTI and staying there unless it is absolutely sure that it can reliably switch to GPS again.

In my view - and to be confirmed by DJI Support - cause of your problem was lack of compass and IMU calibration. This still leaves question to DJI why Spark did not give you warning about that.
If Spark did not warn you about calibration because compass and IMU was calibrated fine, I see a hardware of firmware issue which should be fixed by DJI. Spark should never switch back and forth between GPS and ATTI willi-nilly because it makes it very hard to control.
2018-6-8
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