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Near crash after Warning:Propulsions output is limited

Discussion in 'Pro/Adv Discussion' started by EmptyHassan, Feb 29, 2016.

  1. EmptyHassan

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    Hey guys
    I am relatively new to flying my phantom 3 prof ( ~5 months) and yesterday was the first major close call I had. I was flying around lake tahoe and my first two flights were uneventful. As soon as I took off for the third I got a warning that the propulsion output was limited to protect battery. I'd never seen this before. Then the bird started to descend and was very difficult to control. Had to fight to bring it back and ended up having to sort of crash land it next to me out of fear that it would hit a tree. I uploaded the log to healthy drones and have included the link. I've read a little about people having similar problems but there wasn't a clear consensus as to what causes it. any insight would be greatly appreciated
    Thanks and happy flying



    HealthyDrones.com - Innovative flight data analysis that matters
     
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  2. msinger

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    The battery was nearly depleted when you took off. That warning prevented the battery from shutting off mid-flight. Next time, it would be best to take off with a fully charged battery.
     
  3. EmptyHassan

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    @msinger thanks for your response. what is the threshold for flying? under 50%? that seems very restrictive
     
  4. msinger

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    Your battery will normally be around 30% when landing. It's better to watch the voltage though.
     
  5. Jsun

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    Under Notifications you can see two messages saying "Mode changed to AutoLanding" and "Critically low power, the aircraft will land now. You can throttle up to reduce the speed of decent "

    That's way you are struggling to keep it in the air. Probably kicked in around 35%. This is the Critical Battery Warning threshold I think, this settings can be lowered in the DJI GO app.

    Edit:
    From the manual: When the Critical battery level warning is triggered and the aircraft begins to land automatically,
    you may push the throttle upward to make the aircraft hover at its current altitude, giving you an
    opportunity to navigate to a more appropriate landing location.
     
    #5 Jsun, Feb 29, 2016
    Last edited: Feb 29, 2016
  6. m0j0

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    Autolanded at 34% that is no bueno. As stated before it is always best to take off on a fully charged battery. However, I am interested in you return to home settings and critical battery settings. Someone will have to look at the logs to determine your voltage when it decided to go home.
     
  7. msinger

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    EmptyHassan, if you want us to take a closer look at the battery voltage, then please upload your log here and post a link back here.
     
  8. EmptyHassan

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  9. John Locke

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    A few suggestions:
    1. Make sure you enable your voltage level to show on the screen right below the percent level in the upper right corner. This allows you to easily monitor battery voltage. This displays your weakest battery, of the four. When you get to 3.6V you should be nearby to land soon, and go easy on the throttle.
    2. Never start a flight unless the battery is freshly charged within a day or two. I always top mine off the night before by turning on the battery (push, then push hold) then plugging in the charge cable. This will insure you are "topped off" and will maximize your flight time.
    3. Check your battery warning level settings. I have my first warning at 30% and critical warning at 10%.
    4. You have a large battery deviation in that battery. If you haven't cycled it yet, that may help with equalization. I'd watch that battery closely, it's not looking healthy. How many chargers are on it?

    I don't think the Go app warning levels correlate to when the craft will initiate auto landing, which is a design flaw IMHO. If you are at around 30% battery and you give it full throttle for an extended time, this will pull down the voltage to a level that may trigger auto landing, even though you're at 30%. The last 30% of battery (assuming you started with 100%) you need to be easy on the throttle, especially if you're over water. If you start with a battery that's less than 50%, you're asking for trouble and the previous sentence doesn't apply. They don't tell you this in the manual, but it's reality. A design flaw in DJI communications IMO.
     
  10. EmptyHassan

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    @m0j0 I dont think it was trying to go home... it was just descending and seemed to be moving with the wind a lot more than usual.
     

    Attached Files:

  11. msinger

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    Yes :)

    The combination of the steep ascent and low battery caused your battery to reach the critical low level. And, when that happened, your Phantom started to auto land at its current location. You had trouble getting it to come back because it was trying to land as you were trying to fly back.
     
  12. John Locke

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    If that's the same battery in IMG4480, the deviation at full charge looks good. Since it's been charged 21 times you should try depleting to 8% to see if that helps with the major deviation you had at ~30% level, per the HealthyDrone report. If you have already cycled to 8% on that battery, then just keep a close eye on the deviation at low battery levels in HD reports. If it continues having a major deviation it may give you problems.

    No, it wasn't going home. A week battery will trigger auto land, not RTH. Losing the RC signal will trigger RTH.
     
    #12 John Locke, Feb 29, 2016
    Last edited: Feb 29, 2016
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  13. flyNfrank

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    It's best to treat 30% as if it was 10%.

    Also the battery will drain down at a much faster rate after 30%.
     
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  14. CaptainDrone798

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    This is a common message when the battery is being quickly drained because you have the stick at max (flying up or forward/back/side). Say it's cold out and your doing max power or trying to fly max power into a headwind. Once you reduce power yourself, all is fine. Your experience with the bird going weird and out of control may have just been an over reaction on the controls on your part.
     
  15. EmptyHassan

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    Thanks for the help. Will deplete it to 8% and charge it back up and see how it does. Just glad I didn't lose my baby :)
     
  16. John Locke

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    Mike,
    I don't see the steep ascent before the auto land trigger. Your report is fantastic, but it shows the OP was slightly descending in the seconds before auto land trigger, with hardly any movement horizontally. But the voltages being so low at takeoff is what caused this problem.

    Interesting to note, the trigger of auto land started at 3.274V (lowest cell) and 13.216 total volts, registering 37%.

    Here's a recent flight summary of one of my flights shown below, using your "Log Viewer". At 30% it's shows a total voltage of 14.20V. That's a whole 1volt delta versus the OP's 13.216V at 37%. Then, look at his total voltage 10 seconds into his flight, 13.517V and 41%. Compare that to my 40% level below, 14.618, also more than 1volt difference. I'm puzzled why there's such a huge discrepancy of volts versus percent. I would think the percent level number is derived primarily from an average voltage level under an average load, but apparently other factors are in the mix.
    upload_2016-2-29_11-33-6.png

    I think the P3 needs a new gas gauge algorithm.
     
    #16 John Locke, Feb 29, 2016
    Last edited: Feb 29, 2016
  17. msinger

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    I misspoke. It was the sharp increase in speed (not altitude) that led to the propulsion warning.

    The important thing to note is that the battery cell voltage temporarily drops down to a level lower than its resting voltage when the battery is under a lot of load. Since the battery was already low, it did not have much room to drop. If the OP had flown straight out and back at a steady 5 MPH, all would probably have been just fine.
     
  18. John Locke

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    That's what's so strange in this case. For the full 10 seconds prior to the auto land trigger the OP was under 2mph. I don't see an extreme load until after he realizes he's landing. As a result he hustles back to home at 20+MPH in a hurry to get back. Frankly I'm amazed he got it back because he was at -11ft when auto land occured 700' away from home point. Then, a minute later he's 11' above home point, just 10 seconds before landing, but lands -15' below home point. Pretty amazing, and an important lesson. I'm surprised he didn't hit any trees.
     
  19. EmptyHassan

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    yeh I was almost sure I wouldnt make it back. Here is the video in low res if anyone is interested to see

    Does it default to Atti mode when its auto-landing? it felt like it was very difficult to stear and that it was being swept away with the wind.
     
  20. m0j0

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    Before you take your battery to 8% read up on the experiences on this forum. Some have taken their battery to 8% and killed a cell.