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Does a red flash matter for gps lock?

Discussion in 'Phantom 2 Vision Discussion' started by Encantador, Feb 25, 2014.

  1. Encantador

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    Had my first flight in wide open space yesterday, everything went well.

    Today, tried to get GPS lock next to house with clear sky (clear for UK anyway) and struggled. App occasionally turned blue and said 6 and occasionally 7 satellites had been found but I was still getting a alternate green and red flashing light. I decided not to risk it.

    So, does the icon on the app turning blue and saying 6/7 mean you are good to go irrespective of the lights not being all green?

    Thanks
     
  2. Pull_Up

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    Are you in stock Vision mode or have you switched to NAZA mode, by the way?
     
  3. Encantador

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    Naza
     
  4. Pull_Up

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    If by "good to go" you mean take off and fly and see enough satellites to hold a reasonably steady position in the hover, then yes.

    If by "good to go" you mean have an accurately saved "home" location in case of a RTH or in case you need to you Home Lock, no - wait until you see the rapid green flashes that signal a home lock has been made.

    If you are in an area with poor sat reception on the ground then you can slowly ascend over the take-off point and wait until you get high enough to get a good signal (sometimes just head height is enough). I've never failed to get a home lock on the ground but I believe if you climb to get enough sats you would then get the rapid flashes to indicate it had a home location stored. If not you can always manually set "home" using S2 once you have no more reds. Happy to be corrected on this, though - as I said I've been lucky enough not to have failed to get a lock on the ground so far.
     
  5. Encantador

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    Thanks for the reply.

    I did see a rapid green at one point, but the red was going up and down between one and three (meaning green and 1 red, green then two reds etc), the app was showing between 5 and 7 obtained.

    I still have not been able to find anywhere that explains the difference between the lights in the two modes. I assume that in either mode ideally you just want to see a green flashing light to be sure.
     
  6. Pull_Up

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    The rapid flashing green means it has enough of an idea where it is to save that. In flight you can (I think) go down to about 5 sats and it will still be able to come home in failsafe, albeit at a lower accuracy. The slow flashing green (in both modes) means 6 or more sats seen and all is well.

    There's a bit of a crib sheet for the NAZA light signals here: http://wiki.dji.com/en/index.php/Naza-M ... escription
     
  7. Big Ben

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    Theoretically a (course) location can be determined using just two satellites, provided recent data about location/satellites was stored and you didn't move too far from that previous GPS location. Three is enough for a realistically certain position albeit with limited accuracy. Four is better especially for also determining altitude but since the Phantom uses a barometric pressure sensor too which is WAY more accurate GPS altitude is fairly unimportant.

    Look here for a quite readable explanation of the GPS system.

    Basically two red flashes should give a usable GPS location using 5 satellites so if it degrades during flight after a HP flash sequence while purely flashing green you should begin to be more careful with relying on GPS mode with three flashes which indicates an uncertain amount of satellites because it indicates 4 or less.

    If you are flying in open country the chance of losing GPS fix is pretty low. I have been using GPS for almost 14 years now and have basically only experienced loss of GPS position in the presence of interfering obstacles. In the open field that doesn't really happen although sometimes the number of satellites within LOS of the GPS receiver can be as low as 6. If you want to make certain GPS reception will be adequate you might want to check satellite coverage before you fly.

    In the air you quickly lose any blocking objects between the Phantom and the satellites. It's the ideal place to be for a good GPS signal.