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Looking for Trouble ??

Discussion in 'Pro/Adv Discussion' started by Fifty7, Aug 26, 2016.

  1. Fifty7

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    I've read a lot about compass issues when taking off or calibrating around metal objects. I want to fly in the area pictured below to get some pictures of the Gas tanks before they are demolished (to make room for a shopping mall. I know they are made of concrete & metal so my question is, am I looking for compass trouble or should i be ok as long as I'm not taking off from them? I would be taking off from about where the picture was taken so range is not an issue. I see videos of people chasing cruise ships so i want to think this should be fine but don't want to assume anything.

    IMG_7521.JPG
     
  2. msinger

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    You shouldn't run into any trouble unless you fly right up next to them.
     
  3. Meta4

    Meta4 Moderator
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    AS msinger advises, you'll be fine if you are back far enough to film a whole tank.
    And there's no need to get in for a close up of part of a tank.
    [​IMG]
     
    Falcon900 likes this.
  4. tcope

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    When around a lot of metal I find it only affect the Phantom up to a few feet... like 5 feet.
     
  5. Fifty7

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    Thanks all. Yeah I have no intention of getting that close just high enough to get a decent picture and thats if i don't get kicked out of my takeoff spot (its a parking lot for a golf driving range) ;) The ship is my next thing. I know where to go but i need to find a takeoff spot thats not in the park that runs along the water where I've seen them. I also really want to get the cruise ships leaving out of Manhattan (they go right past Staten Island on the way out to the open waters) but need to make sure I stay away from the Verrazano Bridge.
     
  6. mrcrane2u

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    I take off from parking garages with full interference, compass error. But get 5ft off the deck no problems and no errors, i take off in atti mode .display goes green back into gps mode all good

    Sent from my SM-G920V using PhantomPilots mobile app
     
  7. Fifty7

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    I know atti mode means no GPS but does it also mean no compass? if so, does that mean that people who are reporting compass error messages and then crashing could have potentially avoided it by switching to atti mode?
     
  8. kirk2579

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    yea that makes sense,

    opposite would occur though if someone calibrated compass at same spot
    It would look good on takeoff but go bad as it got away from the metal...
     
  9. Meta4

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    No ... you need compass to fly straight in atti (or any) mode
    If you screw up your compass calibration and that forces the Phantom to drop GPS because of the conflicting data, you are automatically in atti mode anyway.
     
  10. Fifty7

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    Ahh ok. When I take off from my backyard i get compass error. Theres a 10'x20' wooden deck area i use and on one side of it is an above ground pool which I'm assuming is causing the error, so like mrcrane taking off from the parking structure, if i take off in Atti mode and switch to GPS when i'm in the air I should be ok as long as I don't calibrate in the area giving me the error?
     
  11. kirk2579

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    good question
    and it would appear likely that using the "switch" to atti mode would allow control.

    it may not completely though, as the FC unit is still assisting flight when in ATTI mode, it basically is just not using the gps system. how integrated the compass is to both modes is the question.

    in my p2 vision plus we could go full manual, never did it but the option was there
    That would have worked without compass... if one could still fly without crashing..lol

    good luck and have fun flying!
     
  12. Amigorick

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    I would make sure I didn't let one of those tanks get between me and the aircraft. They would probably be very efficient at blocking a signal !!!


    Sent from my iPad using PhantomPilots
     
  13. 4wd

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    I'd be more wary that the land round about could have all kinds of junk buried under a normal looking surface.
    Taking off from a spot with metal just below the surface can cause problems.
     
  14. Fifty7

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    I dont intend on getting behind them. The concrete is ten feet thick and i have no idea how much steel is in it.

    I'm taking off from a parking lot, not the land around the tanks so i should be fine


    They were originally going to use explosives and i was hoping to find out when and video from (very) far away but now they say they're going to cut them in pieces from the top down.
     
    #14 Fifty7, Aug 26, 2016
    Last edited: Aug 26, 2016
  15. Reed L

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    No, if you're taking off with a compass error a lot of different things can happen, so bring it down as soon as possible. Try taking off from a different location first, like in front of the house. If you are still getting a compass error then you may have a bad compass. Compass errors have nothing to do with calibrating the compass. It usually means there's too much metal around but not always. Let us know if you do get a clean start up somewhere else.
     
  16. Mocho

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    Fifty7, FYI those concrete tanks will have a HUGE amount of steel rebar in the cement.
     
  17. Fifty7

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    I'm sure they do but I don't plan on getting too close


    Sent from my iPhone using PhantomPilots
     
  18. Vertigo

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    Gyro's should be plenty. Most of my quads dont even have a compass, I dont see why the phantom would need one in attitude mode.
     
  19. Meta4

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    Because thats how DJI have programmed it. It wont fly properly in any mode without a properly calibrated compass.

    Sent from my SM-G900I using PhantomPilots mobile app
     
  20. BudWalker

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    @Fifty7 For this kind of flight my advice is switch to ATTI before motorStart and leave it there. That's what I'd do. Whatever you do, DON'T RTH and disable Smart RTH so that the A/C doesn't initiate RTH on it's own.

    It's not just distance to the ferrous material that matters. It's also the location of the A/C relative to the ferrous material and the direction of the geomagnetic flux. It's not just magnitude. The ferrous material causes a distortion of the geomagnetic flux. An analogy is trying to cross a smooth river in a straight line. A constant thrust angle will get you from one side to the other in a straight line. Throw in a few large boulders, the flow becomes distorted and the thrust angle depends on your location in the stream. But, it's not just the proximity to the boulders.

    Here is a flight where it wasn't just distance.The altitude was 30 meters when a geomagnetic distortion was encountered.
    upload_2016-8-27_5-7-10.png

    The direction computed from the magnetometers became different from what the gyro was saying and a compass error was declared (not shown is the switch to ATTI)
    upload_2016-8-27_5-10-52.png

    This all happened in a location very close to the previous path of the P3 with no adverse effects
    upload_2016-8-27_5-12-52.png

    Many, if not most, of the compass error flyaways occur because the gyros have said one thing and the magnetometers have said another. But, the problem can be that the FC's idea of heading can now be incorrect and an RTH will cause the A/C to fly in the wrong direction.

    On the question concerning the use of the compass in ATTI mode I agree with @Vertigo,,sort of. In the first place the magnetometers aren't the primary source of heading info. After motorStart it's mostly the gyros. But, the real question is, without GPS info what would any kind of heading (gyros or magnetometers) info be used for. The only situation where heading info is used in ATTI mode is in an RTH in which case the P3 will fly the gyros, not the magnetometers