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Advanced 3.4 Miles Out - Warnings Coming Back

Discussion in 'Phantom 3 Help' started by blue_venetian, Mar 27, 2016.

  1. blue_venetian

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    I wanted to put this up here for anyone new to the P3 Pro/Adv so they can learn from my experience and I put it up here to get some questions answered because I'm very new myself and I'm very perplexed at what happened.

    I've been pushing the range. My previous range record was 2.5 miles until this flight which was 3.4. First let me give you some data.

    Weather:
    Historical weather data for time of flight: Temp 57.0 °F - wind direction SE - windspeed 6.9 mph. According to the UAV Forecast app windspeed at the altitude I was flying (400') was 9 mph. The quadcopter's heading was West on the way out (East on the way back obviously).

    P3A data: HealthyDrones.com - Innovative flight data analysis that matters

    Also there are no errors on the battery. Firmware is all updated. Used iPad mini 2. No range mods, all stock except for the props. I have the yellow tipped carbon fiber props. This was my third flight with the new props.

    Here's a screen recording at 8x speed I put on YouTube of the flight record from the DJI GO app:

    So I take off with 98% battery and head out. Everything is very normal on the way there. No warnings. I'm going full speed at 35 mph. I'm watching my battery and the little yellow H that tells you when to return home and it's no where near time yet. So I get to 3.4 miles out with 73% battery left and decide I should head back just to be safe. I hover for about 15 seconds trying to set up my camera for a video of the flight back but I see the yellow H start to quickly move so I stop everything and just come home. So when I start my flight back I have 70% battery still which seems like more than enough. On the way back the yellow H quick moves past the remaining flight time reading so I'm kinda freaking out just going full throttle back home. If you watch the video you will notice that it's only going 22mph on the way home. I'm not flying into the wind so why is it only going 22mph? When I get about half way back I get a warning which says the battery is critically low and the it's going to land itself. This is the same warning you get when the battery only has 10% but the battery still had around 40-50% left. I just kept flying back and the warning disappeared after like 5 seconds so that was very strange. What's odd is that the warning isn't showing up in any of the flight records. What's with that?

    Quick side note: on previous flights I've gotten warnings saying propulsion output is limited to protect the battery (or something like that) so it slows the craft down even though I'm going full throttle. What's with that? Does that have something to do with why I was able to go 35 mph on the way there and only 22 mph on the way back? Also what does the battery voltage mean? Like when it says 3.7 it's green but when it says 3.6 or 3.5 it's yellow and if it says something like 3.4 or 3.3 it's red. When I slow down the battery voltage seems to go back to 3.6 or 3.7 and turns green. Should I not push the motors so hard? What is a safe voltage to stay above?

    Anyway back to the 3.4 mile flight. So there's no danger of hurting anyone or anything because I'm flying over open fields for the most part. If I did run out of battery before getting home I was prepared to land next to one of the many small, country roads so I could easily retrieve the Phantom but I certainly didn't want that to happen. So as you can see from all of the flight data I provided I literally just make it to the home point in time. At the exact moment I got to the home point at 200' altitude it had started the failsafe landing because the battery had gotten to 10%. I want to know why it only took 25% of the battery to get to 3.4 miles but it took 60% to fly back??? On the way back I was flying East and the wind was blowing South East at 9 mph so I really don't think that was the issue. Any info you can provide would be much appreciated and I thank you for reading through this long post.
     
  2. Meta4

    Meta4 Moderator
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    It looks like you flew away downwind and failed to account for the 10-15 mph headwind you had to deal with coming home.
    If you are flying east into a SE wind there is a headwind component and UAV forecast is only a guide.
    You should not assume it is accurate as they don't have a sensor right where you are relaying live data at height.
    If you want to fly distance AND get your Phantom back ... fly away upwind and return with a tailwind.
     
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  3. Multicoptertec

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    Exactly. Let's say your flying at 30mph, no wind. Ground speed and airspeed are equal. If you are flying into a 10mph headwind, your airspeed is now only 20mph.
     
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  4. mdowney58

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    I might be mistaken, but I think you mean ground speed is 20mph.
    Airspeed would still be 30mph

    Sent from my SM-N910V using Tapatalk
     
    #4 mdowney58, Mar 27, 2016
    Last edited: Mar 27, 2016
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  5. blue_venetian

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    I don't understand. If the wind is blowing SE and I'm flying E then I'm not flying into the wind. The wind would be coming from slightly behind, right?


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  6. mdowney58

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    A North wind is blowing from the North.
    If you are flying East, and there is an East wind, you are flying directly into the wind, so it sounds like you were at a 45° angle INTO the wind.

    Sent from my SM-N910V using Tapatalk
     
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  7. blue_venetian

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    Okay that makes complete sense. Sorry for being such a noob. LOL Thank you! :)


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  8. mdowney58

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    You're welcome, and no apologies here.

    Sent from my SM-N910V using Tapatalk
     
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  9. Multicoptertec

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    Correct, it's late, and I'm having my evening grape juice.
     
  10. Sim597

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    Get this app guys, I'm going to post it, it's called Storm and it's by weather underground and has the best wind speed and direction visuals I've found. It also shows jet stream and graphs for all sorts of info, including wind
     

    Attached Files:

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  11. GreggC

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    I have noticed I can avoid the battery warnings by flying just under full throttle, I believe the system recognizes full throttle and huge battery draw,
    as a safety measure it throws battery warnings.
    These warning don't show when I fly just under full throttle.
     
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  12. blue_venetian

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    Kool. Makes sense.


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  13. John Locke

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    In the 1.6 firmware DJI installed a power governor that prevents full power to be applied after the battery reaches 3.6V, regardless of stick position. That's why the battery voltage font color turns orange, an indicator to ease up. At this point you don't have full power anymore and you'll get that message. You need to be close to home at 3.6V and land by the time you get to 3.55V. If you test this you'll notice that full power vertical ascents go from 11mph at 3.7V to 8mph at <3.6V. You'll also notice horizontal acceleration is slower. This governor is to help you conserve battery and prevent battery protection which can shut off all power mid-flight if voltage gets below 3.0V. Typically speaking, reaching 3.0V is only possible in very cold environments using 1.5 firmware (which is flawed). As for the battery gauge, most of us have learned to take it with a grain of salt, it's not very accurate or linear, as you have discovered. It's flawed too. It's better to watch the battery voltage, and be near to home when you reach 3.6V. In normal circumstances 3.6V on a P3P is about 30%, but this will vary a lot. Battery monitoring is not one of DJI's core competencies IMO. With the P4 they changed the voltage monitoring algorithm, too conservative IMO, 3.6V typically registers about 15%, whereas 15% with P3 is about 3.52V. NOTE: These voltages are the single cell level of the lowest cell.

    If you want to dig deeper into your flights, take a look at your battery voltages versus battery percent using msinger's flight log reader. When comparing multiple flights you'll see how inconsistent the DJI battery gauge is. Temperatures will affect things a lot in this realm, Li-Po technology doesn't like cold.
     
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  14. blue_venetian

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    Super helpful, Locke! Thanks! :D


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