Spooky Action at a Distance

Discussion in 'Mavic Pro Discussions' started by Sky Captain, Nov 26, 2016.

  1. Sky Captain

    Sky Captain Active Member

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    Hi All,

    Well, I had my first problem with the mavic a few days ago. I've made about 30 flights so far without incident, it's a fantastic machine. I was flying around a lake far from power lines and using tap-fly as sort on an autopilot so I could concentrate on camera settings. I began getting yaw drift, to the point where I was almost flying sideways, as I could tell from the video feed. The rest of this story is told after reviewing the flight log many times. I then began heading back toward my home point, at which time I got the message "weak GPS signal". It had been showing 18 satellites, and still did, although the strength bars went down to 2 and turned red. The aircraft went into ATTI mode, as it should have, but began flying backwards and drifting sideways while maintaining an altitude of 150 feet. I made sure tap-fly mode was off. When I saw that the mavic was pointed in my general direction I pushed the right stick forward 100 % and got it back above me. I let go of both sticks and it began "toilet bowling", moving in circles above me without any input. I saw that the satellite strength bars were increasing and soon I had control back and was able to land.

    I know that the yaw drift was probably from a bad compass calibration. I had just calibrated it at the park and there were frisbee golf goals not too far away, they may have caused a problem so my bad on that. However, after reading countless posts about the sudden loss of gps, and my own experience, I think the mavic does have a flaw. I think the gps unit is faulty and prone to sudden gps loss. I can understand going from 18 satellites to 10, but going from 18 to 0 in an instant in open country has got to be the gps unit. I don't know how to upload my flight log, if anyone knows how, let me know. IMG_0130.PNG IMG_0130.PNG IMG_0131.PNG
     
  2. EasyV

    EasyV Member

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  3. Kilrah

    Kilrah Well-Known Member

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    Then you got it.

    No, it's the compass. The FC can't do anything more than what you experienced without compass regardless of how good GPS reception is. When compass data is invalid it kind of invalidates the GPS data, which you see in the app by the bar going red. There are 18 satellites, but they're of no use for GPS-based navigation if the compass is not working.
     
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  4. Sky Captain

    Sky Captain Active Member

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    Ah, thanks Kilrah
     
  5. Sky Captain

    Sky Captain Active Member

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    Thanks EasyV
     
  6. Sky Captain

    Sky Captain Active Member

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    Here is the flight record if anyone wants to look at it on healthy drones.com
     

    Attached Files:

  7. Ender

    Ender Well-Known Member

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    The toilet bowl & yawing can only happen if GPS & Kompass DISAGREE about heading.
    But (whyever) the GPS was out of the Equation, the Mavic was in ATTI mode if i got it right.
    So it cant be a compass offset or the Mavic was "lying" about beeing in ATTI.
    And: having some metal meters away does not mess up compass calibration no matter what some manual says. I have been calibrating conpasses for 6 years now and unlike DJI APM & Pixhawk show the actual computed offset values and metal (NON magnetic) in a distance > 2m does not play a role.

    So something is wrong here, and i am NOT talking about the sudden GPS loss which is the most mysterious thing off all taht happened...

    Ender
     
    #7 Ender, Nov 27, 2016 at 1:58 PM
    Last edited: Nov 27, 2016 at 2:18 PM
  8. erkme73

    erkme73 Well-Known Member

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    @Sky Captain - you have described to a Tee what happened to me. And several others. The consensus seems to be bad compass calibrations, and that the observed behavior is 'to be expected'. I've never had this happen with my Phantoms. There is something about these stories that, I think, show a systemic issue. In each case, the GPS is fine until the RTH is triggered, and then as the MP approaches the homepoint, suddenly and unexpectedly, the GPS drops out. In my case, the ATTI mode let the MP race off (at 12MPH in no wind) to a distance of 1000' south of my (and homepoint) location before I started to manually recover. The entire time it was fighting me.

    The first clue I had that something was amiss was the TBE that happened just prior to the RTH execution. Still, during that episode, it was in GPS mode - full signal, no warning. It was only after it reached the homepoint (in a huge arcing circle), missing and drifting away, that I received the error and ATTI notice.



    Note how at 2min 15sec, despite having GPS back on, the bird flew against the stick inputs. Something was amiss. I'm still not convinced it was a bad calibration, but until someone proves otherwise, it looks like that's the story.
     
    #8 erkme73, Nov 27, 2016 at 2:14 PM
    Last edited: Nov 27, 2016 at 2:19 PM
  9. Sky Captain

    Sky Captain Active Member

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    Love how it headed straight for water! Yeah, clearly this compass gps disagreement is happening way too much. Let us pray now for a firmware update
     
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  10. erkme73

    erkme73 Well-Known Member

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    Well, FWIW, I did another calibration, nothing metallic on or near me. Third flight out, and boom... TBE on one pause. Curiously it was just after getting a warning about controller interference - which happened during my epic near loss a few nights ago.

    Here's today's circular adventure:



    Notice how it goes from the middle of the yard, shoots south, then starts circling the drain - all without any directional stick input.

    If it really is a compass calibration issue, I really think the next step is to be buck nekkid in the field by my clubhouse. Watch the evening news for the highlights...
     
  11. Anthony

    Anthony Well-Known Member

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    Have you reported this to DJI Support ?? as i am sure the more good examples like yours with the data to back it up will help us all in the long run.

    Thanks for posting this.
     
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  12. bruceC

    bruceC Member

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    Kilrah: very new here, what is FC and where is the listing of acronyms and abbreviations? Thanks - bc
     
  13. Multicoptertec

    Multicoptertec Well-Known Member

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    FC = Flight controller.


    Sent from my iPad using MavicPilots
     
  14. bruceC

    bruceC Member

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    thanks - and listing of acronyms and abbreviations?
     
  15. Kilrah

    Kilrah Well-Known Member

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    Never seen one, but that's not DJI-specific anyway, just usual multirotor talk.
     
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  16. bruceC

    bruceC Member

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    OK.. thanks
     
  17. niclariv

    niclariv Active Member

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    I really hope that anyone who's having issues like this are reporting them to DJI (not just putting them on this forum). From reading all the threads about this issue it does seem like there's an issue with some of the Mavics that doesn't exist for the Phantoms, as others have said above. Hopefully it's not a hardware problem and can be addressed with a firmware update, and in order for that to happen everyone who's had this issue should be contacting DJI. Personally I worry because I live near a park that will be great for test flying my Mavic when it arrives (supposedly shipping tomorrow), but if it takes off on its own as others have described, there's a hill with a fairly busy street in two directions. If I don't have control of it, there could be a major car-drone accident. One thing I wonder is if those of you who have had this issue and say it felt like the drone was fighting you have attempted to control the altitude? At least if that were possibly I could fly it high above the traffic while attempting to regain control.


    Sent from my iPhone using MavicPilots
     
  18. niclariv

    niclariv Active Member

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  19. bruceC

    bruceC Member

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    I understand your concern and also hope these incidents are being reported to DJI. Found my Mavic at the Apple store 8 days ago and have only flown it twice, indoors. This is my first quad, if you discount the Blade Inductrix RTX Ultra Micro, also only flown inside. I have read and re-read the manual, watched and watched again DJI instructional videos and many many youtube videos on calibration.... Reading through Mavic Pilots Forums and DJI Mavic forums and seeing all the reports of RTH issues worries me. Frankly I am very reluctant to turn the Mavic loose in the wild without knowing my instincts will be good enough to know precisely how to make it come home. I live on the CA Central coast and we have many good days to fly and that first flight will come. But, I would like to see a software update to remedy the flyaway/TBE.
     
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  20. Sky Captain

    Sky Captain Active Member

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    I will say that the mavic did hold altitude steady throughout the incident, giving me time to regain control.
    Also, I know DJI Ken and others are monitoring these forums and I invite any of them to contact me and I will upload my flight logs for review.
    In the meantime I'm going to do some flying with very careful attention to getting a clean compass calibration.
     
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