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Why Did My P4 Auto Land with 15% Battery Left & 17.3 Feet From Home?
584 11 2017-6-7
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BearDrone
lvl.4
Flight distance : 2887251 ft
United States
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Okay, this is an odd one. Firstly, P4 was not damaged and it landed from an altitude of about 5 feet onto my grass lawn. I was 29 feet from the set home point when the Go4 App came up with a message that said, "Warning: There is only enough battery to return to home. Return to home now".

My low battery warning is set to 25%. My critical battery level is set to 10%. I rarely push the limit on either. I had just brought the AC back from a flight across the bay, and I was flying in my front yard just because I like to practice manuevering in tight quarters when I can. Nothing crazy, slow and easy. Just a bit of back and forth, maybe one loop of 20 yards.

When I got the above message, I thought, okay, I'll turn around (from 29 feet away) and come back to land. Again, I'm 29 feet away, and maybe 5 or 6 feet off the deck.

Then I get:

"Low power. Aircraft is returning to home"

Then there is a Landing symbol at the top left of the app, and she just goes down into the grass. Not a hard landing, but it certainly did not look controlled and gentle.

This all happened pretty quickly. Looking at the app flight record the time line was:

Flight Time 22:45- 25% battery. Low battery indicator tripped. 871.1 ft from home point. Elevation is 396.9 ft. I start bringing AC home.
25:31- 16% battery. Warning indicator telling me to return to home now (as discussed above). 58 ft. from home point. 13.1 ft. elevation
25:41- 16% battery. Two messages appear. One is a "Tip" indicating that obstacle avoidance will be disabled. The other is saying, "Low power. Air craft returning to home." 29.4 ft. from home point. 13.1 elevtion (this is above sea level, I am assumming. The AC is maybe 4 feet off the deck now). The word "Landing" also appears in the upper left at this point.
24:45- 15% battery. AC lands in the grass 17.3 ft. from home point. I did not try to override with the left stick up position. It happened so fast (4 secs.), I couldn't get my thumb on it in time.

This is odd behavior to me. I have certainly flown the AC close by when below 15% battery without this auto landing occuring. Again, I'm right in my front yard, not .5 miles away. I'm ready to land, but did not. My critical level is set to 10%, not 15% as it would seem.

What is concerning is the 4 seconds between the warning that says "Air craft returning to home" and then the air craft actually landing. It made it approximately 12 feet.

I also understand that the % usage left on the battery indicator is an estimate based on multiple variables. You would think the algorithm would take into account the proximity of the home point when the auto landing feature was tripped. I had no fewer than 16 satellites in the P mode during this entire flight.

If it matters, I was using a HiCap battery, fully charged the night before.
2017-6-7
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KM5RG-Robert
Captain
Flight distance : 2075213 ft
United States
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I wonder if since it was within the 65ft circle when it initiated RTH if it just landed in place because of that.
2017-6-7
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Cabansail
Second Officer
Flight distance : 136686 ft

Australia
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"13.1 elevtion (this is above sea level, I am assumming. The AC is maybe 4 feet off the deck now)."

Your aircraft has no reference to sea level only the home point. Altitude is measured with a barometer and uses the air pressure at the home point to set zero.  A variation of 8-10 feet is very small change in air pressure. The air pressure does vary due to many factors over time and the barometer can also drift slightly.

Think people will need to see the flight log to do more than speculate about the landing issue.
2017-6-7
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Labroides
Captain
Flight distance : 9991457 ft
Australia
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The % indicator is only a rough guide and the lower the %, the rougher it is.
What matters is what voltage your battery can supply and voltage drops as the battery level drops.
Once the battery can't supply enough juice to keep things going, the Phantom will autoland to preserve itself.
You can see the actual voltages if you go into your flight data.
Go to http://www.phantomhelp.com/LogViewer/Upload/
Follow the instructions to upload your flight record and look at the report it provides.

ps .. lowering the battery warning levels isn't a smart thing to do.
Having a safety margin is a very good policy.
Landing between 20-30% helps if you want to take the Phantom home every time.
2017-6-7
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DJI-Jamie
DJI team
Flight distance : 112405 ft
United States
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If the failsafe is activated automatically or manually within 20m (65ft) of the home point, it will self land.
2017-6-7
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microlinux
Second Officer
Flight distance : 2576969 ft
United States
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I find it helpful to to tie the battery display to one of the programmable buttons so I can periodically check voltage.
2017-6-7
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BearDrone
lvl.4
Flight distance : 2887251 ft
United States
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Labroides Posted at 2017-6-7 15:23
The % indicator is only a rough guide and the lower the %, the rougher it is.
What matters is what voltage your battery can supply and voltage drops as the battery level drops.
Once the battery can't supply enough juice to keep things going, the Phantom will autoland to preserve itself.

Thank you. I'll take a look at the voltages in the sequence things occurred. In reference to changing the battery level warnings, I do land with no less than 20% every time. The reason I changed it is because of the annoying beeping coming from the RC. This brings unwarranted attention to the pilot in a variety of public situations that may not be conducive to safe operation. So, I just want the beeping to stop. I'm not trying to milk the battery or anything else.
2017-6-7
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BearDrone
lvl.4
Flight distance : 2887251 ft
United States
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DJI-Jamie Posted at 2017-6-7 16:29
If the failsafe is activated automatically or manually within 20m (65ft) of the home point, it will self land.

Ah, well, that explains it. So if I were outside of that 65 ft. diameter, I assuming I would have been able to have a chance to land it manually?
Thanks for the info.
2017-6-7
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BearDrone
lvl.4
Flight distance : 2887251 ft
United States
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microlinux Posted at 2017-6-7 17:14
I find it helpful to to tie the battery display to one of the programmable buttons so I can periodically check voltage.

That's a fantastic idea. Now, I just have to figure out how to do so.
Appreciate the tip.
2017-6-7
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DJI-Jamie
DJI team
Flight distance : 112405 ft
United States
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BearDrone Posted at 2017-6-7 17:27
Ah, well, that explains it. So if I were outside of that 65 ft. diameter, I assuming I would have been able to have a chance to land it manually?
Thanks for the info.

No problem! Your notion is correct. Even when it's auto landing, you should have some horizontal control over the aircraft to avoid obstacles. If this was a voluntary RTH command, you can press the RTH button on the RC or the app to cancel it.
2017-6-7
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BearDrone
lvl.4
Flight distance : 2887251 ft
United States
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DJI-Jamie Posted at 2017-6-7 17:29
No problem! Your notion is correct. Even when it's auto landing, you should have some horizontal control over the aircraft to avoid obstacles. If this was a voluntary RTH command, you can press the RTH button on the RC or the app to cancel it.

Jamie,
No, this just happened on it's own. I was just about to get it turned 180 degrees and head over to my home point, when it just went down after flashing a message. I was not quick enough.

Since nothing catastrophic occurred, I think I will get the battery voltage screen loaded on one of the custom buttons, or just have the voltage on the main screen. That way, I can get a better idea of where I really am versus relying on % estimates of the software.

Thanks again.
2017-6-7
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Gregrog
lvl.1
Flight distance : 1152966 ft
United States
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This is from the firmware update I have been having problems also. I have my battery warnings at 25 and 10% also. Just like you I like to fly around my yard when the battery gets low, but I have been having issues also after update. This will start landing and will not always cancel before trying to aggressively land itself. Have had 3 crashes after update. Once you get below 25% and it thinks it needs to return home it should come up with a warning that it is returning home but I think they have shortened the time to cancel this. And at 10% this thing is landing and you can't cancel the landing anymore you can only throttle up and you haft to be aggressive or it will land and sometimes hard.
2017-6-8
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