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Critical low battery RTH
2934 6 2015-10-5
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Homer J

United States
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I was in an area with many large trees when I was about to land the craft - probably no more than 15 feet off the ground.( I had walked a distance from where the drone took off from)  the battery level was just about the hit the critical low point which I believe is 10%.  I am guessing the RTH function kicked in as the craft suddenly began to go straight up.  
I thought I read someplace that when this feature activates the craft will assend to a certain altitude before returning to the home point?   I was under several large trees and the drone was headed right into them.  In a panic I tried to override the feature by moving the control sticks when the drone took a hard left turn and crashed through a few smaller trees and hit the ground.  It appears the only damage were some scuffed up props as it landed on its top.

   My question is was this sudden increase in altitude becasue of the kicking in of the critical low battery RTH function?  If so, what is the quickest way to override this?   If I had just let the craft do its thing, it would either be hung up in the top of a tree or crashed from a much higher altitude probably causing much more damage.  I understand I should have landed before I hit this low battery level but I was just a few seconds away from touching down.
2015-10-5
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tmygun1
First Officer
Flight distance : 2972497 ft
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Low Battery Warning is Different from Low Battery RTH Warning AND Critical Battery Warning.

Low Battery Warning simply tells you your battery is getting below a certain level of charge.  The default setting is 30% but in the DJI Go app you can set it anywhere between 50% an 15%.  You get some obnoxious beeping, and a soothing female voice telling you low battery, but other then that nothing.

Low Battery RTH (or as I like to call it "You Are Too Damn Far From Home For Your Battery!" warning) is triggered by a combination of how far you are away from your home point and what your altitude is at the time.  The further and higher you are away from your Home Point the sooner or earlier Low Battery RTH will be triggered.
It can happen at 30% when you get the default low battery warning or anywhere between 30% (or higher) and 10% depending on how close/far you are from the home point.
Low Battery RTH warning gives you 10 seconds to cancel the RTH by stopping it on your Go app screen or hitting the RTH button on your RC.  The default RTH behavior when triggered, is for the P3 to go straight up to the Failsafe altitude (30 meters by default), and then go directly to the home point and land. If the P3 is within 65 feet of the home point, when RTH starts,  it will land where it is unless you cancel.

Critical Battery Warning is something completely different.  If the battery gets below 10% the aircraft will give you a critical battery warning AND 10 seconds latter will start landing right where it is.  The only way to override this (and it's not really an override) is to push the altitude control in the full up position and the aircraft with hold it's altitude long enough for you to take action to move the P3 horizontally to a safer landing area.
For instance, your over a pond and get Critical Battery Warning (Less then 10%). after 10 seconds the P3 start to descend (water or no water) to the pond.  You hold your altitude control full up and it will maintain it's altitude while you move it to a dry landing area.  As soon as you let go of the altitude control stick it will continue it's decent.  
I've always felt that when you near 10% you are in a danger area anyway.  I've only learned this from testing, testing, testing.

Hope this helps.
2015-10-5
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Homer J

United States
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thank you tmguy1 for the explanation... it does help

I'm quite sure I reached the critical battery point(10%)   but the craft did not try to land but went higher.  Is this not a feature of the return to home for it to reach a certain altitude before retuning to home
2015-10-5
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tmygun1
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The one way you know if you hit the Critical Battery Warning, is you will get that soothing female voice that will proceed to tell you "Critical Battery" and  "The Aircraft Must Land Immediately" and "Danger Will Robinson!" or something close to that.
When you hit Critical Battery there is no RTH.......Just LRN "Land Right Now".  Again you can override the decent and maintain altitude but not ascend.

I think its a DJI failsafe.   If you are 1/4 a mile away and 50 feet off the ground, I would not think 10% battery will give you enough time for RTH to ascend, say to 100 feet and fly back a quarter of a  mile.
I think what DJI is trying to avoid is a P3 falling out of the sky from heights unknown.  Better to have a forced controlled decent then, having a battery shut off and a P3 falling from 100 feet like a rock.
2015-10-5
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Homer J

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got it... I'm not sure why I thought it was assend to a preset elevation before returning to home -  I thought I saw that in a video someplace?  maybe not
    Not sure why the craft decided to go up on it's own but I guess I learned another lesson about what not to do
2015-10-5
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tmygun1
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Homer J Posted at 2015-10-5 10:34
got it... I'm not sure why I thought it was assend to a preset elevation before returning to home -  ...

My best guess......you were not quite to Critical Battery Level (and honestly Critical Battery level is really 9 1/2 % not 10%), but were just a short distance from your home point (but more then 65 feet/20 meters), and Low Battery Level RTH kicked in at @ 10%, and up she goes.

If this is the worst thing that ever happens to you and your P3......count your lucky stars and consider yourself a good pilot.
A seasoned airline pilot friend of mine once said "All pilots make mistakes...were only human....but training and dedication to always be a better pilot, no matter how long you've been flying, should help keep those mistakes small and manageable".
2015-10-5
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ksunsingh
lvl.3

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tmygun1 Posted at 2015-10-5 06:31
Low Battery Warning is Different from Low Battery RTH Warning AND Critical Battery Warning.

Low Bat ...

that soothing voice tho =]
2015-10-5
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