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Altitude - Is it AGL

Discussion in 'Phantom 2 Vision Discussion' started by guyatl2000, Jul 15, 2014.

  1. guyatl2000

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    I often fly in a mountainous area. If for example I am using the ground station feature and launch high up over a valley, does the Phantom operate at AGL (above ground level) or based on the altitude of that where it is launched from? IE, does AGL actually change with the terrain? My worries are that I could crash into a mountain if the Phantom does not recognize the change of terrain.... Any thoughts?

    THANKS!
     
  2. RCRookie

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    No your altitude is set at home point and does not change. Unless you reset it at a new altitude. (S2 Switch cycled 5 times).
    So anything between you and the craft not accounted for when using RTH will be a collision hazard.

    At no time will the craft automatically change its altitude with exception to RTH (66ft/20m). It will rise back up if in a canyon or valley as long as its initial home point was set above there.

    Example: You start your Phantom at 300 ft ground elevation. It sets home point. You fly down into a valley or ravine, intitate RTH and the craft will rise to its initial launch elevation of 300 ft "plus" it will add the 66 feet before returning home. If you initiate RTH already above the 300 feet initial home point elevation it will return home at that altitude.

    Waypoint Navigation makes no difference in how altitude is stored or used by the Phantom Vision.
    So its best to fly up to the altitude you want...Do a visual check of obstacles or tree top elevations before setting the waypoint altitude indices for the mission.
     
  3. MikeON

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    [/quote]No your altitude is set at home point and does not change. Unless you reset it at a new altitude. (S2 Switch cycled 5 times).[/quote]

    Resetting the home point doesn't reset the altitude. At least not with my P2V. I had noticed this before but just finished a test flight to be sure. Went 250' away and 200' altitude. After resetting home point, distance read zero, but altitude still read 200'. Brought it closer and descended to 50' above launch point (original home point). Reset home point again. Altitude then read 50'.
     
  4. ProfessorStein

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    I think you're misunderstanding what the reset does.
    It doesn't reset the altitude to zero. It resets the altitude of the home point itself to whatever the current altitude is. If you're at MSL, and launch your Phantom from the ground, the altitude of the home point will be zero. Now you fly to 200', and reset the home point, the altitude of the home point will be 200'.
    This comes nicely into play when/if you use the RTH function, and RTH will rise 20meters/60' above the altitude of the home points altitude. So if you know the tallest trees in your flying area are 200', you fly to 200', reset your home point, and now you know that should you ever need to use RTH, it will rise to 260', easily clearing those obstacles. (As long as it's still below your ultimate flight ceiling).

    At least, that's how it works with my Phantom. I've tested it several times.
     
  5. MikeON

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    Yep- you're right. I just went out and tried it again.
    Reset home point at 40' altitude. Altitude read 40'. Then initiated RTH. It climbed to about 100', where it would have been about 60' had home point still been at zero. I let it autoland and it came smoothly down to ground and landed. I then relaunched and reset home point at 13' and initiated RTH. It climbed to 73' and started to autoland, at which time I resumed control.
     
  6. MikeON

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    Today I tried a couple simple Ground Station missions combined with Home Point resets.
    First, I reset Home Point at 40' AGL. Placed waypoints 1 and 2 short distances away, accepting the default altitude of 98'. Pressed GO and it climbed to 98' and stayed at 98' for the whole mission.
    Then, I reset Home Point at 110' AGL. Placed waypoints 1 and 2 short distances away, accepting the default altitude of 98'. Pressed GO and it descended to 98' and stayed at 98' for the whole mission.
    Apparently, Ground Station altitudes are based on AGL at launch point, not the Home Point altitude (if reset different from launch point). Otherwise, I would have expected the missions to occur at 138' and 208' respectively.
     
  7. ProfessorStein

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    Good to know... but not unexpected. When entering altitudes like that, I would expect it to be absolute, rather than relative.