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Standard RTH - Starting Above Ground Level

Discussion in 'Phantom 3 Help' started by Paulndot, Jan 7, 2016.

  1. Paulndot

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    I hope this hasn't been discussed elsewhere - I searched but couldn't find anything. If I initiate the home location at the top of a hill, or in this case, on a cliff overlooking a canyon or valley, will the RTH feature remember that "home" was at that altitude? Should I be worried about flying at say an altitude of 800ft in the valley, and have the RTH feature drop down to the predetermined height - essentially crashing into the side of the mountain on its' way "home" if I'm at an observation point at a1200ft altitude?

    I'd like to get some shots on our next trip to the mountains, and planned on doing exactly that - starting at the top, and flying the drone in the valley beneath us.
     
  2. bbfpv

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    When the HP gets recorded, that is elevation 0. Everything else is in relation to 0. If you take off from a cliff with a RTH altitude set to 100m, if you fly down 100m into the canyon and initiate RTH, your bird will climb 200m to reach your 100m RTH altitude setting.
     
  3. DAP-UAV

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    The app will display a negative altitude as you drop below your home point altitude accordingly.
     
  4. Paulndot

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    WOW - thanks for the quick response folks! I thought that was the maximum height for flight? In the Smart RTH section of the manual (pg. 11) it states that the aircraft will ascend to the RTH alt and return to the home point. So - I guess I can set the RTH alt. However, in the Low Battery RTH section, it states the aircraft will return at the CURRENT altitude (not good if I'm in the valley). However, according to what you are both saying, the altitude should be zero at the cliff and increase (in negative numbers) as I descend, so it would climb back to zero and up to whatever altitude I set in the RTH settings.

    In the Failsafe RTH illustration (pg 13, block 5) it shows the aircraft heading straight to the home point (if the alt. >20m) or ascending to 20m if below. The description really doesn't do much to explain, except that the aircraft cannot avoid obstacles during the Failsafe RTH. So, if I lose signal and it starts the RTH...seems like it will hit anything between it and the Home GPS point.

    So the only "safe" RTH is the manually started one, which uses the preset RTH altitude. Does that sound about right?
     
  5. bbfpv

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    Kind of. If the bird is below the preset RTH altitude, it will climb to that altitude and RTH. If it is above the RTH altitude, it will RTH at its current altitude. Yes, it will hit anything in the way on its RTH flight, there's no denying that. But your biggest concern should be hitting critical battery level, because if the bird calculates that it cannot safely RTH on the juice currently left in the pack, it will land where it is.... bad news if it's still in the canyon.
     
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  6. Paulndot

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    Thank you...
     
  7. yawnalot29

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    I would still be cautious and leave lots of room.

    I crashed my P2V+ due to height not being accurate (not in RTH mode)

    Flew up to about 150 feet AGL from a hill side that is about 650 feet ASL (according to sone topo map). Flew out over ocean in GPS mode. Then flew back using ATTI mode (had 13 sat lock when toggled over to ATTI mode). End up crashing into side of hill that is about 150 feet below where i was standing. Did not change altitude once i got it up in air figuring i would be OK.

    Before you ask, i can hear the quad and was searching for it in the sky above me (not below me).

    I suspect had i activated the RTH, the result would have been the same as i set my RTH at 150 feet.
     
  8. Meta4

    Meta4 Moderator
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    Flying in atti mode, the P2 would fly faster BUT it would always lose altitude.
    Had you been in GPS mode, your Phantom would have come home safely.
     
  9. Meta4

    Meta4 Moderator
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    When your Phantom tries to land at the recorded home point, it doesn't care about the altitude of the home point.
    It will fly to a point above home and descend until it can't descend any more (it's landed).
    Whether it is above or below the actual recorded home point makes no difference.

    Easy to test this by taking off and resetting home to the current location of your Phantom 10 metres up (over a clear area of course).
    Fly more than 20 metres away and activate RTH.
    Your Phantom will climb to RTH height (if not already at or above RTH height) and fly to above home.
    It will then descend and keep descending until it feels the ground beneath its feet.

    Of course you don't need to let the Phantom do the landing and can cancel and take over at any time.
    Most flyers can see and land better than the blind autoland system.
     
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  10. yawnalot29

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    Yeah. That will teach me to trust the manual. :))

    ATTI.jpg
     
  11. Meta4

    Meta4 Moderator
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  12. Paulndot

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    Thanks...