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FYI - Critical bug/logic flaw in battery calculations for RTH/Land
1046 16 2015-11-4
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tdrussell1
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I'm hijacking someone elses high-bloodpressure experience to describe this, as he did an excellent job documenting the event and the actions he took to recover.  In brief, the logic to control when the Phantom will Land based on battery level is either bugged or flawed, leading to LAND events at high battery levels.  I realize this isn't a trivial acusation, but i think we have sufficient empirical and anecdotal evidence to support it.  Re: Those many, many discussions about their Phantom going into LAND mode at high battery levels.

I think this image and the user's description alone is enough to illustrate the issue:


The issue appears to be that the copter makes the decision to land based on the location of the current battery life indicator between the H and zero battery, rather than basing the decision on the actual battery life.  This makes zero sense and has caused several crashes and near misses, and even a stolen phantom, based on browsing these forums and others groups.  

The bottom line is that the decision to LAND should never be invoked at anything greater than the absolute minimum battery level necessary to make it to the ground, with appropriate buffer.  

Mitigation:  Until we see an update to change this behavior, it appears inadvisable to fly the battery down to the RTH trigger, especially at long range.  Understandably the calculations are approximate (though as specific as possible, certainly), but a sudden jump in the RTH trigger location caused by a gust of head wind appears enough to trigger a LAND.  

Recovery: If this happens to you - your instinct is to look up at the copter (or mine is, anyway).  Keep your attention on the screen, and be prepared to CANCEL the land and/or RTH order.  Unless your battery is actually very low, you should always be able to cancel the land command.  At this point you should have regained control of the copter, at least until you hit your predefined critical battery level.

I would be extremely surprised if DJI weren't aware of this, so my intention is more to highlight the issue to pilots so they can recognize when it occurs and how to get home safe.  

2015-11-4
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john
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I have experienced a similar problem.  Reported it a couple months ago.  My drone landed in a banking parking lot with 46% battery life left.  Scary..

Im impressed with your distance..11,000 feet plus..How did you do that?

John
2015-11-4
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tdrussell1
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john@security-s Posted at 2015-11-4 23:41
I have experienced a similar problem.  Reported it a couple months ago.  My drone landed in a bankin ...

Not me - a user in a facebook group.  But, i've seen people hit some impressive ranges out over water, partly because there's no interference and partly because water will reflect RF rather than absorb it.
2015-11-4
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arives
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tdrussell1 Posted at 2015-11-5 00:32
Not me - a user in a facebook group.  But, i've seen people hit some impressive ranges out over wa ...

I wonder if the RC battery was running low? Happened to me that way. No warning by the way that I noticed either audible or visual.
2015-11-4
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arives
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tdrussell1 Posted at 2015-11-5 00:32
Not me - a user in a facebook group.  But, i've seen people hit some impressive ranges out over wa ...

I wonder if the RC battery was running low? Happened to me that way. No warning by the way that I noticed either audible or visual.
2015-11-4
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tdrussell1
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I'm going to bump this once for the Thursday crowd and then let it fade into the distance...
2015-11-5
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Flight Raptor
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Flight distance : 1332034 ft
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What IS this "H" value that is showing on the battery status bar????   That "H" in that image is much further to the RIGHT on that battery status bar than mine is showing.

I really wanna understand this to prevent a potential disaster in my own flights!   How do you set/change this "H" value?
2015-11-5
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sportsfan4393
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Flight Raptor Posted at 2015-11-5 09:08
What IS this "H" value that is showing on the battery status bar????   That "H" in that image is muc ...

The "H" values "represents the point when the battery level is just enough for the aircraft to return to the home point." The farther distance you go out, the more to the RIGHT the "H" will go. In this case, I believe that his glitched and moved way to the RIGHT after it was already too late. Therefore, causing it to LAND
2015-11-5
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Flight Raptor
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sportsfan4393 Posted at 2015-11-5 13:23
The "H" values "represents the point when the battery level is just enough for the aircraft to ret ...

Wow..........this is a very interesting post....I very much appreciate the heads up and appreciate your explanation for this 'H' value.   

Yet something ELSE I need to keep an eye on!
2015-11-5
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sportsfan4393
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Flight Raptor Posted at 2015-11-5 11:05
Wow..........this is a very interesting post....I very much appreciate the heads up and appreciate ...

No problem! I am glad you asked, because I wanted to do a little more research myself to try to avoid this from happening. Win Win!
2015-11-5
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Geebax
Captain
Australia
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DJI are in a difficult situation here, if they don't get this right, then someone's drone drops into the sea and the owner then comes on here claiming it is DJIs fault, not their own and wants the aircraft replaced. If they err on the conservative side, then a discussion like this arises. Frankly, if I was going to fly that far out over water, I would want the aircraft to be conservative in its calculations. But then again, I would not fly that far out over the water, too risky.

Without a discussion with the appropriate DJI software people, we do not definitively know what factors they take into account in calculating remaining battery life, but from what is said, it appears they try to take into account wind gusts and other factors that may affect the duration of the flight. A case of damned if you do, and damned if you don't.
2015-11-5
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Flight Raptor
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Geebax Posted at 2015-11-5 15:58
DJI are in a difficult situation here, if they don't get this right, then someone's drone drops into ...

Overall I agree with your philosophy, but with 55% battery remaining (look at the image), no way in hell should your copter go into automatic LANDING mode!

None of the mathematical calculations and algorithms are going to be 100% accurate.   
2015-11-5
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Geebax
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Flight Raptor Posted at 2015-11-6 08:10
Overall I agree with your philosophy, but with 55% battery remaining (look at the image), no way i ...

I just realised that we are talking about LAND mode rather than RTH mode, in which case that is a concern. I had not picked up on that before, sorry.
2015-11-5
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tdrussell1
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Geebax Posted at 2015-11-6 05:15
I just realised that we are talking about LAND mode rather than RTH mode, in which case that is a  ...

The OP was a little jumbled in this regard, i cleaned it up some.
2015-11-5
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Geebax
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tdrussell1 Posted at 2015-11-6 08:19
The OP was a little jumbled in this regard, i cleaned it up some.

I wonder if it might be practical to be able to specify a 'do not use land' option for when it is flown over water. That way is must do an RTH, or at least attempt it instead.
2015-11-5
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quikdom
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I'd like a minimum height option for flying over water too :-)
2015-11-6
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Fat City
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quikdom Posted at 2015-11-6 09:07
I'd like a minimum height option for flying over water too :-)

I'd like to second this idea for a new minimum height feature. I had a close call recently that this would have prevented.
2015-11-13
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