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In-flight Unexplained Oddity
535 11 2018-2-12
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Spaceman_66
Second Officer
Flight distance : 81575 ft
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I flew my new MA for the first time this past weekend. On Saturday, I experienced something unusual that concerns me. I was on my 3rd battery, just doing some slow clockwise (looking down) yaw pans. Out of the blue the MA started making unusual rotor sounds that immediately raised concerns. Surprisingly, my FPV feed (to an iPhone 7) showed the front left prop guard / rotor were in the picture (I flew that first day with the stock prop guards installed). I managed to initiate a video recording while it was happening, but it went away in just about 3 seconds later. Total duration of the event was a handful of seconds (10 maybe?). Definitely a heart-pounding few moments there.

Here's a still I grabbed from the video to illustrate what was going on. I'll attempt to pull down the flight logs ... again ... DJI Assistant 2 (the latest version) disconnected from the drone in mid-download, and subsequently I couldn't ever get it to see the drone again. I try again tonight.

Anyway, any idea what might have happened? I don't recall seeing any error messages from DJI Go 4, but I was wondering if perhaps an odd sudden gust of wind might have caused an uncommanded right yaw, in which case I could see the gimbal freaking out and trying to compensate with a normally-unencountered extreme left yaw. Just speculation, of course, but where I live we do experience unusual "vortex-like" winds at times. For the record I'm flying with the latest versions of EVERYTHING.

Any clues would be appreciated. Are there any ways us "lay" folks can delve into / view the black box data from our AC, or does it require a high priest or priestess and "special sauce" software?

Joe

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2018-2-12
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Spaceman_66
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...sorry, I should have included MA or Mavic Air in the thread title itself, mea culpa...

Mods feel free to rectify; I can't find a way to edit the title.
2018-2-12
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Maxi3D
Captain
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A gust of wind? How high up were you?
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Tadango
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The prop guards come in the camera very quickly.
2018-2-12
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Spaceman_66
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Tadango Posted at 2018-2-12 12:49
The prop guards come in the camera very quickly.


Thanks - that's good to know; never had it happen with the Spark. They were only on for Day 1 initial conservatism. From here on I only see putting them on for indoor flying and maybe occasionally otherwise when & if appropriate.

It's still concerning, as the bird's rotors were very definitely making "not normal" sounds and in the video you can see the prop guard is actually fluttering, whether that is a reaction to an externally induced oscillation (wind gust? I don't recall getting any wind warnings from DJI Go 4 whatsoever) or perhaps from an on-board vibration source that remains to be determined. The audio modulation I heard during the event suggested rhythmic prop RPM variations.

Again, hopefully the black box data will fill in the pieces.
2018-2-12
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Spaceman_66
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Maxi3D Posted at 2018-2-12 12:45
A gust of wind? How high up were you?


IIRC (I'll later confirm when I can get all the flight data off the AC) I was at or near my flight altitude limit (self-imposed for multiple reasons) of 120 feet AGL, or 2000 feet above sea level (my local ground level is at like 1880 feet above sea level - very high desert, with rugged peaks close by [like 1/3 - 2/3 miles away] all around me in most directions except to the south).
2018-2-12
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Montfrooij
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Might be the combination of wind and prop guards indeed.
Maybe some vibrating that oscillated with the guards?
2018-2-12
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Spaceman_66
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Montfrooij Posted at 2018-2-12 13:13
Might be the combination of wind and prop guards indeed.
Maybe some vibrating that oscillated with the guards?

That's absolutely possible - something may have hit a resonant frequency and the control system FW didn't like it one bit!
2018-2-12
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Montfrooij
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Spaceman_66 Posted at 2018-2-12 13:36
That's absolutely possible - something may have hit a resonant frequency and the control system FW didn't like it one bit!

It will be hard to confirm for me not having a MA, but even for DJI to replicate this.
But it might be the cause.
2018-2-12
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Supong
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The camera gimbal is 3D. I think it can turn left or right a bit before centering itself and that is how the propguard show in the camera briefly. You may try again doing the yaw to see if the assumption is true.
2018-2-12
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Spaceman_66
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Supong Posted at 2018-2-12 17:10
The camera gimbal is 3D. I think it can turn left or right a bit before centering itself and that is how the propguard show in the camera briefly. You may try again doing the yaw to see if the assumption is true.

I could absolutely see it lagging if, for example, you tried doing a full-stick rudder/yaw while in sport mode. But I was in tripod mode, intentionally trying to do a super-slow cinematic yaw to pan the horizon (something like one 360 deg rev in 30 seconds or so).

But I am currently leaning towards thinking that a sudden wind gust pushed the yaw rate for a few seconds to a value high enough that the camera gimbal reacted the way it did, resulting in the vibrating/fluttering prop guard appearing in the FPV feed for a few seconds, accompanied by the odd pulsating prop/rotor sounds. This could well have been amplified by something hitting a resonant frequency that the flight control system couldn’t properly cope with. Hopefully the black box data will eventually help to unravel the mystery of just what the heck happened, mainly so I can learn from it and ensure it doesn’t happen again.

Nobody ever wants their drone exhibiting unexpected and arguably “weird” behavior. It’s ultimately a matter of trust.
2018-2-12
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Supong
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Try setting the gimbal mode to somethingelse or remove the propguard.
2018-2-12
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