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GPS Speed

Jay KickliterJay Kickliter Posts: 446
edited 2008-12-10 20:20 in General Discussion
I'm·doing a Propeller based balloon project. I·want to log both the ground speed and ascent/descent rate.·Does anybody know if GPS speed takes into account of Z axis movement or juist X&Y?

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2008-11-21 15:37
    Z-Axis is included on GPS in the form of altitude, though I can’t say how good the accuracy is. Pretty much all GPS units support altitude (including ours), however high-end units will often employ a separate pressure sensor to help make altitude readings more accurate.

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    Chris Savage
    Parallax Engineering
  • SRLMSRLM Posts: 5,045
    edited 2008-11-21 18:54
    My *guess* is that it doesn't support z axis in the speed measurement. Logically, most applications don't rise or fall quickly enough for it to matter.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2008-11-21 19:18
    Jay,

    Why not just log the Lat/Lon/Alt coordinates and calculate the velocities later?

    -Phil
  • Jay KickliterJay Kickliter Posts: 446
    edited 2008-11-21 21:45
    Phil, I think that's what I'll do. See, another idea I had was to monitor decent rate, and if it exceeded a certain threshold, that meant that the balloon bursted and should be cut away. I may still pursue that later, but for a first run I should try to keep it simple.
  • SRLMSRLM Posts: 5,045
    edited 2008-11-21 21:59
    But if you cut the balloon, then you just fall faster (unless you have a parachute)
  • Jay KickliterJay Kickliter Posts: 446
    edited 2008-11-21 22:17
    There is a balloon. The whole idea would be to ensure that the balloon remnants don't tangle with the parachute. But, I think I'm over-complicating things. Given a big enough separation, it shouldn't happen. I do have to have a cutdown device by law, in case the ballon doesn't burst at altitude. I started a new thread about that one.
  • sylvie369sylvie369 Posts: 1,622
    edited 2008-11-21 23:24
    I think you mean "there is a parachute", right?

    AFAIK, in these high altitude balloon projects, there's always a parachute suspended below the balloon, to recover the instruments after the balloon bursts. I assume that's the law as well.

    www.kaymont.com/pages/home.cfm
  • kelvin jameskelvin james Posts: 531
    edited 2008-11-22 18:19
    You could do a diy vario / altimeter, it looks like reading it with a propeller wouldn't be too complicated.


    A couple of links to check.


    http://www.sparkfun.com/commerce/product_info.php?products_id=8161


    http://www.pixelproc.net/altivario.html


    **
  • achilles03achilles03 Posts: 247
    edited 2008-12-10 20:20
    Just FYI, you don't need a cut down device if your payload meets certain FAR requirements (under 6 lb, a mass/area ratio below some threshold, etc).

    Dave
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