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Fog triggers obstacle avoidance...
688 7 2018-2-25
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Oldmaninwva
First Officer
Flight distance : 8726381 ft
United States
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Was flying a little yesterday morning, was up on top of a hill where I usually fly from but the town below was fog covered...  Thought Id take a few shots while I had a little time...  While I was up and lazily puttering above the fog a sudden change in the weather brought in a denser and higher bank of fog so I started back..  wasnt long before my P4 was engulfed in the “Cloud”..  No worries, well above the trees and only about 2000ft away so I cranked it up to bring it home, but in less than 30 seconds I get the warning signal from the forward obstacle sensors and the ac stopped in the sky and hovered...  after releasing the throttle I again pushed the stick forward, knowing that I was still well above any obstacles and it resumed its flight home.  This action repeated 4 times before I got it back to land.  
The only thing I can think of was water droplets from the fog may have gotten on the sensors lenses and tricked it into thinking there was something there.

I know I could have pressed the RTH and the obstacle avoidance would have been turned off, and it would have just returned normally.  This was a first after more than 100 hrs in the air.
Anybody else experience anything similar?
2018-2-25
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DJI Elektra
Administrator
China
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Hi, there. Glad that your drone was back home. We would not recommend users fly through fog and cloud and it is really dangerous. Please fly in recommended environment.
2018-3-4
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Geebax
Captain
Australia
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That's an interesting one. I have heard of the sensors being tricked when flying towards a low or setting sun, were you perhaps flying towards a rising sun?
2018-3-4
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Bashy
Captain
Flight distance : 549140 ft
United Kingdom
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Fog, mist, snow, rain, sun, cloud (just fog really) all will set off the avoidance system, its when the moisture droplets are seen by the system and it thinks its too close to an object, been there, done that, i mostly fly with the sensors off now, more so because i dont fly where i can hit anything at the moment/
2018-3-4
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Blériot53
Captain
Flight distance : 1939754 ft
France
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I'm with you, it would seem likely that the condensation formed on the sensors would trick the obstacle avoidance. As you say, RTH would have worked. How about if you'd turned the bird through 180 degrees and flown back in reverse?  Since you knew there were no obstacles between you and the drone, that could work.A cautionary tale to us all, however, about the risks of flying in adverse conditions.
2018-3-8
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Oldmaninwva
First Officer
Flight distance : 8726381 ft
United States
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Blériot53 Posted at 2018-3-8 23:17
I'm with you, it would seem likely that the condensation formed on the sensors would trick the obstacle avoidance. As you say, RTH would have worked. How about if you'd turned the bird through 180 degrees and flown back in reverse?  Since you knew there were no obstacles between you and the drone, that could work.A cautionary tale to us all, however, about the risks of flying in adverse conditions.

Yep, could have flown backwards too...  I have also considered the turning off of the obstacle avoidance sensors altogether since most of the time I fly open space.  I just don't completely trust the bird when there's the possibility of a flyaway.  The P4 I have now has over 400 flights on it and in that time it has acted erratic and once when coming in for a land it decided it did not like the geomagnetic conditions st the time and went crazy, ended up 50 ft away flying under a tree, raised itself into the finger branches and tipped itself and shut down...  Lucky it fell into some higher grass upside down so there was no damage..  That happened so fast that no thought was given to switch to ATTI.
2018-3-9
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Blériot53
Captain
Flight distance : 1939754 ft
France
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Oldmaninwva Posted at 2018-3-9 02:20
Yep, could have flown backwards too...  I have also considered the turning off of the obstacle avoidance sensors altogether since most of the time I fly open space.  I just don't completely trust the bird when there's the possibility of a flyaway.  The P4 I have now has over 400 flights on it and in that time it has acted erratic and once when coming in for a land it decided it did not like the geomagnetic conditions st the time and went crazy, ended up 50 ft away flying under a tree, raised itself into the finger branches and tipped itself and shut down...  Lucky it fell into some higher grass upside down so there was no damage..  That happened so fast that no thought was given to switch to ATTI.

The only mishap I've had in a year of droning extensively, was just a couple of weeks ago, and that was pilot error.  Having taken off from behind a low dam wall (in the lee of the gentle wind) to overfly some local reservoirs, I completed the circuit without dramas and came in to land.  As the drone dropped below the level of the wall, the wind effect was cancelled and consequently the drone clipped the wall and broke the tips off two adjacent props. Enough of an impact to eject the battery, and the whole lot dropped a couple of feet onto tarmac.  It was an "OH,CR@P!" moment.  After a careful and anxious inspection, no other damage was discerned, so I replaced the props and spun up the motors. Had a few minutes testing the controls and all was well. Subsequent flights have been OK.
One thing I did notice - when the battery fell out, obviously the recording stopped instantly, so no video of the crash.  But the date stamp on the next video was reset to 1 Jan at 00h00.  Subsequent ones have shown the correct date an time, without any input from me.
2018-3-9
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Aardvark
Captain
Flight distance : 384432 ft
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United Kingdom
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"I know I could have pressed the RTH and the obstacle avoidance would have been turned off, and it would have just returned normally."

That would depend on how 'RTH Obstacle check' had been set in 'Visual Navigations Settings' / 'Advanced Settings' menus. Even with Obstacle Avoidance disabled then it can still be made to operate by default if an RTH is initiated.
So you could, if you wish have Obstacle Avoidance off all the time for general flying, but still have the peace of mind it would work if RTH required. In the case you mention above then only having OA completely disable for RTH would have made a difference.
2018-3-9
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