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Relationship between Compass & GPS re: ATTI mode

Discussion in 'Phantom 2 Discussion' started by pianoflyer, Mar 9, 2015.

  1. pianoflyer

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    Hi, There is something I can't quite get my head around and can't seem to find in the manual.
    If the Home Record point is being locked by GPS during start up and doesn't require the compass calibration , how are they related?
    IE, a friend of mine (seriously, not me) neglected to calibrate his compass when at the beach, he sent the Phantom way out over the water and suddenly lost connection. He then realized that it was flying in the direction of his actual home ( which was the last place he had flown and calibrated-15 miles over the mountains). It appeared it was doing a RTH but not to where he started at the beach. He chased after it when it was over land and was able to re-establish connection and fly it back to him. So it wasn't RTH to his current start point (which is why, I assume. he should have re-calibrated the compass) So in a related thought ...when I fly by cheap toy quad (no GPS), by staying in range I never lose connection, no worries......but are flyaways on the Phantom caused by losing connection with radio (which I would think would force a RTH) or losing connection with the GPS or Compass connections that the Phantom makes during startup....In that case, does switching to ATTI mode, negate all the GPS info and allow my to fly the Phantom back to me (assuming LOS) without any interference from some confused or lost GPS or Home info(I hear people joke about it trying to "Fly back to china") but again, if I switch to ATTI, do I have total control to fly it back relying on the signals from the radio just like when I fly my cheap quad?......I know I am covering a few issues here...but hopefully they are related enough to make sense.
    Thanks for your patience :)
     
  2. Meta4

    Meta4 Moderator
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    They are not related at all.
    GPS is about geographic position and the compass is about direction - the two are unrelated.
    You need to make sure your compass is calibrated so when the Phantom's brain tells it to fly 137° to RTH, that is what it does rather than some other direction.
    And you don't have to calibrate every flight. Your friend's issues had nothing to do with compass calibration.

    Only if you are within signal range. Atti won't do much good if your Phantom has gone out of range.
     
  3. pianoflyer

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    I appreciate your help. I think what I'm trying to understand is if you let the phantom perform the correct startup and if the signal is lost, it is supposed to RTH. So, how is a flyaway theoretically possible. If I lose orientation, I just use homelock in IOC, and if it flies out if range, it should RTH. So the rare flyaways are occurring since it loses GPS or what? Thnx again.
     
  4. Meta4

    Meta4 Moderator
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    It's commonly believed that many of the reported flyaways are indeed due to operator error and improper understanding of Phantom operation. Often the Phantom does not fly away at all but drifts on the wind but this is reported as flying away.

    How is it theoretically possible?
    If the home point is not recorded properly before flying, in a RTH situation, the Phantom will not have a good home point to return to. If your GPS sats drop to less than 6, the Phantom will default to atti mode. It's still flyable with control but if it gets out of range it will drift wherever the breeze takes it. It will be unable to RTH without sat lock.

    Fortunately loss of sat lock is quite uncommon in normal flight but it did occur more with the early P2V+ with inadequate shielding for the GPS. If you are out of range and out of GPS, you are out of luck.

    Another factor is that the RTH speed is lower than normal flight (no-one knows why DJI did that). So it's possible in windy situations for the RTH Phantom to fail to make headway against the wind and never get home. Flying off downwind in very windy conditions is asking for trouble.
     
  5. TeamYankee

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    The causes of fly-aways are many and varied, but they nearly always have an "operator error" component...
    eg. leaving the wi-fi enable on a Gopro or flying too close to radio transmitter mast etc etc. The list is endless...

    The issue is that the RC signals can be spoofed by other transmission sources, giving the impression that the quad is under control, but it's not you at the sticks, it's random radio noise doing the flying!

    It's entirely possible that he could have taken off before the home position was recorded. On startup there should be 2 sets of rapid green flashes.. one for the "system ready" and one for "home position" - if you take off on the first green flashes then the home point may not be recorded at all, or it will record a home position somewhere along the current flight path... so an RTH situation can appear to be a fly-away as it's going to the wrong place.

    It's all fun and games!
     
  6. Meta4

    Meta4 Moderator
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    Interference gets blamed a lot but is very rare and is unlikely to "take over" a Phantom.
    A much more likely result of interference that is strong enough to affect the Phantom is that your Phantom simply loses signal and returns home.
     
  7. TeamYankee

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    I was referring to the GoPro issue.. leaving the wi-fi enabled and going for a flight.