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Flying down below you

Discussion in 'General Discussion' started by Siddy, Jun 8, 2013.

  1. Siddy

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    New flyer picking up advice.

    How does the phantom fly going below you i.e. I want to video flying towards dams of reservoirs etc and fly up the wall and over to the dams.

    Does it throw the gps out etc?

    Siddy
     
  2. DeweyAXD

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    I'd not risk it in GPS mode as it seems very sensative to being blocked and satelites are line of site based so there is no guarentee they are directly upward. Better to learn to fly well in Ati mode and I believe you will actually get better, smoother footage too.

    The real issue you will find is judging distance unless you are either using FPV or if the sun is directly behind the Phantom casting a shadow (not ideal as it will be in the footage).
     
  3. tanasit

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    RE: satellites are line of site based.
    I am not positive that is the case. The car GPS can be anywhere under the roof (out of line of sight) and works fine.
    I flew my Phantom indoor on second floor with 1 floor above me and the GPS found 4-5 satellites (confirmed by one green and either 1 or 2 red flash).
    Another member replaced the stock GPS with a better one and got > 6 satellites with 2 floors above.
     
  4. DeweyAXD

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    Sorry what I said was a little misleading as you rightly state.

    GPS can track through objects (including the plastic lid of the body and as stated even roofs if given enough time as I too have experianced to my surprise).

    What i mean by line of sight is that satelites are not always 'straight up' above you. One or two of them that the Phantom locks onto can be out there in space just above the horizon. Assuming you start flight on top of the **** then when you drop below a the wall there will still be a few directly above but the **** but the link with the ones over the horizon may break (especially likely with a thick reinforced structure). It will usually pick up others pretty quick that are directly above it but just bare in mind that when that link breaks, GPS mode will not be functioning on 6 sats and hence stability can be affected.... not what you want if your props are 4 feet from a solid concrete structure with a big drop.

    My understanding of how the GPS works in the Phantom is that when it loses 6 satelite lock it will act like its in Ati mode and hence won't stabilise itself when you let go of the sticks. For that reason its good practice to learn self correction in Ati mode before you try it in GPS mode near such structures. Likelyhood is that GPS will be faultless but better to be safe than sorry ;)
     
  5. tanasit

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    RE: Ati mode and hence won't stabilise itself when you let go of the sticks

    In ATTI mode it will still level itself and hold attitude but in won't stay in spot in space.
    So you are still in pretty much control. In addition, even without the required 6 satellites or more locked in, you still have the CL that uses the compass to save your Phantom from running away.
     
  6. Racklefratz

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    If you do some internet research, there's a lot of information out there on GPS, how it works, and factors that can affect its performance. The signals are line of sight, and will pass through non-ferrous materials like clouds, glass, and plastic, but will not pass through anything ferrous, buildings, or mountains (or dams). A common issue with GPS signal degradation is poor signal geometry, meaning the receiver is in a position that makes triangulation difficult, affecting position accuracy. This situation is somewhat self-correcting, since the GPS satellites and the earth are always moving.

    What you'll find, if you haven't already, is that distance will be your biggest issue; at some point the Phantom will be so small it will become difficult to see which way it's going.
     
  7. old5town

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    The times have changed one thing to consider is home land security might take a different view at what you are doing flying up and down the face of a dam. Food for thought.
     
  8. Racklefratz

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    Not a far-fetched idea at all - good point. And, they probably have satellites up there that can see you doing it. But it's for your own good - they're just "keeping us safe".
     
  9. mercillus

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    Thanks for the laugh!!! Needed that.
     
  10. Siddy

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    I see what your all saying, So I need to fly out from the top turn round the drop the copter then fly towards and up the wall. That way I can see it come over the top onto the dam then fetch it back to me.
     
  11. Racklefratz

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    It should go without saying that unless you're using FPV, you need to keep the thing in sight or risk crashing into the dam if you plan to get close to it - and even WITH FPV, the dam very likely could block your video downlink. And watch the wind; a large vertical structure like that can do strange things to wind currents.
     
  12. mmcbain

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    Here is a little video of a guy flying a quadcopter off a small mountaintop and into a valley, just to inspire you:

    https://www.youtube.com/watch?v=ZBRZHLbyts8

    DHS should have better things to do than concern themselves with a 33-class hobby quadcopter flying around a lake, although one should never underestimate bureaucratic stupidity; after all, a Phantom was shot down in Turkey a few days ago.

    As everyone seems to have pointed out, reliable flying of the Phantom depends on it having about 6 satellites in view, which gives plenty of redundancy for a 3D position. Make sure you have a home lock before you fly. Your dam flight will present few technical difficulties under FPV conditions--you are very [very, very] unlikely to have GPS problems flying over a body of water :cool:. Of course, if you run into the wall, you are likely to have difficulties retrieving your airframe, unless it magically washes up on the shoreline [they tend to sink].

    Michael McBain
    Melbourne, Australia