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Advanced Height on ground not zero

Discussion in 'Phantom 3 Help' started by stuart_m, Jul 25, 2015.

  1. stuart_m

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    Hi Group
    I've been flying my P3A for a few hours - so far so good. Had a couple of issues today, they might be related:
    1) With aircraft on ground before first flight and props spinning, height on Pilot app shows -0.6 m, rather than 0. This was with 10 + satellites shown on the GPS signal.
    While slowly ascending height decreases - so I saw -1.0 m about 1 m above ground. Height went through zero and displayed around +1 m when I estimate aircraft was 2 m above ground level.
    This happened from first flight and did not change when stopping motors. I did not power off/power on the aircraft.
    Similar issue with distance on Pilot app - showed about 1 m when at home point, rather than 0.

    I have seen posts on the P2 mentioning the barometer displays height.
    Can anyone confirm the height on the P3 is from the GPS, rather than an internal barometer?
    Any idea on the GPS update rate in the P3A?

    If I stop the motors, does this reset the Home position, or do I need to power off/power on?

    2) (and probably my fault) Low voltage alarm came on and I was probably too slow landing, trying to get closer to me. At about 1 m from me and 1 m estimated height, critical battery alarm came on and aircraft rapidly rose. I assume this was the RTH kicking in. Aircraft then hovered about 10 m above ground, I had no control of altitude by Controller. Continued trying to regain control of height. Aircraft rapidly descended (I assume under RTH control). I applied some "up" on the Controller which slowed descent, but aircraft hit ground.
    I accept this was my fault - but to try and learn from this experience should the Controller override the RTH?

    Maybe related to 1) above, does RTH descend and land under "height" control, so the aircraft stops motors when at zero height, or does the VPS take over? Or does it hover above the home point waiting for a controlled land.
    I want to understand more about how RTH works before trying it out.

    Firmware on aircraft and controller updated 2 weeks ago. Using Pilot app on iPad mini 2 running iOS8.4

    Thanks in advance for your help

    Stuart
     
  2. RoyVa

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    I think you will find that most pilots will tell you that the height OSD is off when the craft is on the ground. The quad doesn't use that info to land. It uses internal sensors that tell it when there is a change in descent and it has touched down. Has to do with the altimeter, baramoter, and other sensor providing data to the main controller.
    Mome position is established when you power up the unit and it gets its GPS satellite lock. You can change the home position durning flight using the S2 switch or by utilizing dynamic home position. The manual give more info on both of these functions.
    The RTH function is initiated two ways. One by loss of signal or critical low battery. There is a RTH height adjustment in settings. If you are lower that that height and RTH kicks in it will climb to that height. If you are higher that RTH height setting it fly at the higher height until time to desend. It lands under sensor control telling it had touched down and movement has stopped. Not using the OSD height but using sensors. Hope this helps.
     
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  3. stuart_m

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    Thanks RoVa
     
  4. cleaner1369

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    I thought that was what the VPS was for, measuring small distances to the ground...

    Oops, that's right...the VPS ISN'T WORKING NOW, IS IT?

    Month-and-a-half and waiting...waiting...waiting...

    Oh well, Visa says my deadline to return my P3Pro is August 1st. There WILL be an update or else it IS going back for a refund.
     
  5. hudiaratama

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    I have the same problem

    Height status about 1-1,5meters on the ground..even I already calibaret couple times or turn off & on the drone / rc

    Easily to take off manually but can't do auto take off because the DJI Pilot App thought that I already fly about 1-1,5meters off the ground..

    Otherwise return to home button works fine
     
  6. redmoe

    redmoe Guest

    Same issue here mine will increase in height error throughout the flight usually 20ft off. If this measure is purely gps it make sense as the consumer grade accuracy in altitude is not that great. I find it much easier on the craft to manually land anyway.

    The VPS has nearly cause me to crash land a couple of times. Hopefully there is an up date soon.
     
  7. stuart_m

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    Thanks for your replies.
    Must admit I take off and land manually. I have noticed VPS errors soon (iOS) after taking off, but this does not seem to affect hovering a few inches above the ground.

    Had an interesting one a few days ago. Aircraft was on the ground with props idling after a few minutes flying. Props slowly sped up and then aircraft slowly ascended to about 2 m and hovers. All this was with hands off the controller, I watched ready to take control, just to see what it would do!
    I was flying early in the morning and the nearest house is over 100 m away, so no wifi interference.
    I think this is a hint to not trust the aircraft and always be in control!

    I'll be exploring Atti mode soon - that WILL be fun :)

    Cheers guys

    Stuart
     
  8. bbfpv

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    That's a big no-no. Never let the bird idle while on the ground.
     
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  9. N017RW

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    +1 w/bbfpv

    It's a known 'condition' that left idling the quad 'thinks' it's still flying, hovering actually.
    As sensors drift it will make corrections accordingly and often results in a tip-over.

    There is no real idle ;)
     
    #9 N017RW, Jul 29, 2015
    Last edited: Jul 29, 2015
  10. stuart_m

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    Understood, no 'idling' from now on!
    I guess it's a case of learning by experience, some common sense and this forum :)

    Many thanks!
     
  11. AlmostTan

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    You are getting mighty close to that deadline...