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How Does P3P RC Know Its Location?

Discussion in 'Pro/Adv Discussion' started by Great Pumpkin, Jan 4, 2016.

  1. Great Pumpkin

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    Did a test yesterday to see if DJI has really put airport avoidance into P3P firmware. Within a mile of a Class C airport, my P3P RC would not even turn on. Moved 0.7 mile farther away, it turned on OK but said it couldn't connect with the Phantom. Moved another 0.2 mile farther from the airport and all was well. I didn't intend nor try to fly because I knew I was within the airport's airspace.

    The GPS and Glonass signals are received by the Phantom, not its RC, so the P3P's position is transmitted to the RC (and thus to the iPhone, tablet or Android) via Lightbridge - am I right? So how did the RC know not to turn itself on when close to the airport, and neither the Phantom nor the iPhone 6 were turned on?

    Before you rag on me for being irresponsible near an airport, know that I have been flying a P2V within the same airport airspace for two years, always with the knowledge and permission of the airport's tower personnel for every single flight within that airspace. And know that it was not my intention to fly yesterday - and I didn't - just to test whether or not the P3P and its RC would even respond near the airport. Answer is that the RC did NOT turn on within one mile but did about two miles away. And yes, I tried several times without success, and I reiterate, I did not intend or attempt to fly at either location.

    And to continue with a related question, when the GO app gives a distance and a height for the Phantom, is that from the Phantom to the Home Point or to the RC? And if to the RC, then how does the Phantom know where the RC is located unless they are communicating by differential GPS???
     
    Trackman1 likes this.
  2. LuvMyTJ

    LuvMyTJ ADMINISTRATOR
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    It uses HomePoint to know where it is in relation to lift off. Are you saying the TX would not power on? Never heard of that happening.
     
  3. Oso

    Oso

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    I assume you know that the RC does not have its own GPS, so it doesn't know where it is unless it is connected to a GPS enabled device such as most Android devices, cellular iDevices, or an external GPS of some sort. Without that, it's only the Phantom (bird) itself that knows where it is.

    I have never yet heard of an RC not turning on at all such as you described.
     
  4. alokbhargava

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    That's the secret :)

    No, RC doesn't have GPS and can't compute its location on its own. I'm surprised with your findings.

    P3 knows the home point, but that can be changed to your new location if your connected device has GPS.
     
  5. BigAl07

    BigAl07 Moderator
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    While I guess it's possible my P3P transmitter (Tx/radio) is of an older version it would turn on. I was at the local airport (Class C airspace) with a flight instructor (BFR time) and we were standing probably 300' from the published Airport Reference Point (standing beside one of the utility hangars next to the flight school). We were talking about the P3P in terms of commercial operations and he was interested in seeing what the display/Ap showed in terms of map etc. I connected my Ipad min2 to the TX and fired them up. The Tx did power on and I was able to run the DJI Go App although it was not connected to the aircraft (didn't even try powering the aircraft on for obvious reasons). I got no "Alerts" even though I was standing on airport property because neither my Tx nor my Ipad Mini2 have any GPS acapability.

    I don't feel that simply turning your Tx ON is in any way a problem or irresponsible or anything what so ever. Powering on your aircraft might be another story :)
     
  6. Great Pumpkin

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    Yes, sorry LuvMyTJ, I meant TX, and yes, it would not turn on within one mile of the airport but did two miles
    away.
    I think I'll try the same experiment today with only the TX.
     
  7. Great Pumpkin

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    The mystery deepens - I've returned to the site where TX didn't turn on within 1 mile of the airport, and this time it turned on there - no problem. So why didn't turn on a couple days ago? I don't have a simple answer, and I'm not going to lose any more sleep over it.
     
  8. Meta4

    Meta4 Moderator
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    I can't answer the original question. It seems unlikely that the controller wouldn't turn on.
    But I can answer the second one.
    There are two distances in the bottom of the app.
    The first one D is the distance of the Phantom from homepoint.
    [​IMG]
    The second one is the distance of the Phantom from the controller (if the tablet/phone has GPS)
    [​IMG]
     
  9. Great Pumpkin

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    Thanks, Meta4, for enlightening me about distance for the P3P and doing it so illustratively. Where is that beach in your photos?