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RTH altitude

Discussion in 'Phantom 2 Vision + Discussion' started by nynelyvz, Oct 28, 2015.

  1. nynelyvz

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    Question is, I took off from a high ridge. Climbed to 35 feet above me. Flew out out a meadow approx 100 feet lower then my HP. I did not change my altitude at all during the flight. Altitude on the app reported I was 35 feet throughout the flight. Lost signal to phantom 2 v3 and it went into RTH. It turned and flew back to me at the HP but didn't climb to my RTH altitude of 150 feet that I have set. The flight log in my Litchi app shows an altitude change at the time of RTH go from 35 feet to 150 feet. I watched the video and it did NOT climb. Is there something in the Vision plus that would recalculate the altitude above the meadow. Which if it did that would make sense, being the Phantom was about 150 above the meadow. I was thinking it would still use the 35 feet above HP and climb approx 115 feet higher before RTH. Hope I am making this clear. Any ideas. Thanks
     
    #1 nynelyvz, Oct 28, 2015
    Last edited: Oct 28, 2015
  2. Meta4

    Meta4 Moderator
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    Your Phantom doesn't know if it is 15 feet or 15000 feet above the meadow.
    It seems unlikely that it didn't climb to RTH altitude especially if the flight log indicates it did.
    1
     
  3. GadgetGuy

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    It is very difficult to determine 115 feet of ascension in place from merely looking at a video taken at 150 feet above the terrain below it. The Litchi app reports it did ascend appropriately. The bigger question that would confirm your suspicions of a failed ascension to 150 above your launch point would be from what altitude directly above your launch point did it descend during the last phase of the RTH? Was it 35 feet or 150 feet? Your eyes would not deceive you about that!
     
  4. RoyVa

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    Apparently it must have figured the AGL was at the proper height and RTH brought it back. Would be good if someone in a hilly terrain could test it to see how it calculated. From home altitude take off or from ground level when RTH is initiated. My way of thinking would be from ground level at its location. That being said would require adjusting the RTH from the lowest point you would be flying taking into account the take off and drop in altitude when the in a valley and adjusting the RTH from lowest level to the ground level you are on and adding the difference into the RTH for safety sake. Crazy but then have to be careful that RTH doesn't get it to high if you are over ground level and it initiates RTH...... Ok someone test it over hilly terrain and report back. Good find!
     
  5. GadgetGuy

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    Meta4 above already confirmed that there is no way for any Phantom to determine AGL (except for VPS within 9 feet of the ground). It only knows Home Point as 0 and measures from there, regardless of the terrain below it, so something is askew with the OP's experience. It certainly isn't because of some mysterious, unknown and completely undocumented AGL calculation ability.:rolleyes:
     
    #5 GadgetGuy, Oct 28, 2015
    Last edited: Oct 28, 2015
  6. nynelyvz

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    Operators experience is a 20000 hour airline captain that completely understands AGL, MSL and any other altitudes necessary for aircraft. Just wondering why and if it should have climbed . So for some reason it did not. But it did return safely and if necessary I would have climbed it. Thanks for your tactful and informative responce.
     
    #6 nynelyvz, Oct 28, 2015
    Last edited: Oct 29, 2015
  7. BlackTracer

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    Did the altitude change step from 35 ft to 150 ft in the log? Or did it follow a slope to that altitude over time?

    The phantom can only sense barometric pressure at the HP then sense changes to that baseline to determine current height.

    This one is mysterious.
     
  8. nynelyvz

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    Yes it did show a gradual climb. Yeah I don't get it either. Like I said I was thinking it would think it was at 35 feet the whole time then climb an additional 115 feet to 150 feet above the HP (launch point) But when it did return it was still about 35 feet above me. IDK one of those Phantom mysteries. I will try it again with a screen recorder on and see exactly what happens. Thanks Black Tracer.
     
  9. GadgetGuy

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    Hoping I didn't offend. Just trying to correct the prior poster. It is unfortunate that the Phantoms cannot discern AGL. Knowing this makes your experience all the more mysterious. You saw what you saw, and the Litchi app thought it did ascend. :confused: Do you have the .SRT file to go with the video? It shows the relative barometric elevation in meters synced with the video as a Subtitle overlay. However, you need to enable the .SRT recording feature in DJI GO. If you haven't already, you might want to turn it on. Very helpful in cases like this.
     
    #9 GadgetGuy, Oct 28, 2015
    Last edited: Oct 28, 2015
  10. nynelyvz

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    No its all good GadgetGuy. It just seemed strange I got so many confirmations yet the Phantom didnt climb. Thats why I posted this. Just to see if anyone else experienced anything like it. But this is a Vision 2 plus v3. Isnt the GO App for Phantom 3? Anyway I am going to try it again with a screen recorder. Thanks
     
  11. GadgetGuy

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    My bad again. DJI GO is indeed only for the P3 and Inspire1. In terms of trouble shooting, if you were flying with Litchi instead of DJI Vision, I would look there for why it didn't ascend but "thinks" it did.