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Incorrect altitude display

Discussion in 'Phantom 2 Vision + Discussion' started by Emmbee, Aug 27, 2014.

  1. Emmbee

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    Hi,
    Another newbie needing help.

    Altitude display in app shows anything from -20 to -50 ft whilst at ground level before take off.

    When in flight it sometimes, but not always corrects itself to what I consider to be about right.

    Have done advanced calibration twice, with no results - should I be concerned ?

    Thanks for your help
     
  2. Fplvert

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    I would suggest you do a compass calibration and reconnect. The altitude should be close to 0' and distance 0' as well. Then you know you have a good home lock. Good to ask before you make a $1300.00 mistake! :D
     
  3. Panamon Creel

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    The altitude is calculated via a barometric pressure sensor that is integrated into the Naza-M controller so compass calibration or GPS lock have no influence on it. Do you get large alt fluctuations while on the ground with the motors off? How stable is the altitude when you're hovering on a spot?
     
  4. Emmbee

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    Thanks for the response.
    Just tried compass calibration - same result.

    Good home lock as verified by second set of green flashes/distance shows zero/H shows in ground station/symbols and figures are blue / ten sats.

    Hmmmm....
     
  5. Emmbee

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    Thanks again,

    Just tested again.

    Display fluctuates between -35 to -45 whilst stationary with motors off.

    Couldn't test fly - too windy in this part of the UK
     
  6. Fplvert

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    I'd be concerned about that fluctuation. The concern for me is a RTH is based on H/L altitude + 20 meters. I think there could be a chance of that being too low. Maybe try advanced calibration again and see if your # are stable and within specification. Make sure the bird is on a level vibration free surface. Let us know how it goes. :)
     
  7. bizrank

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    Though I've read all the threads I could find, I too am not sure why the altitude for the Phantom Vision+ varies at startup. I've had negative readings as large as -20 or -30 feet. (Positive values are always much smaller.) Other times, the elevation reading seems right--very close to zero, which is what it should read, inasmuch as the altitude reading has nothing to do with sea-level. Like you, I have tried compass calibrations and IMU calibrations, both advanced and basic, but without predictable corrective results. The comment on barometric pressure is intriguing--but wouldn't a barometric determination mean that our phantoms would appear to vary in altitude according to the weather? High or low pressure systems would wreak havoc, no?

    Could it be that the phone hosting the DJI app has anything to do with the app readout, I wonder?
     
  8. Panamon Creel

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    The barometric sensor is influenced by low or high pressure weather systems but the value is being reset every time when you start-up your Phantom (every 20 minutes or so) and won't get a significant enough pressure change in that time period (if you did you'd likely run for shelter anyways :) )
     
  9. N017RW

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    Agreed.

    I also wonder about atmospheric pressure changes compared the time of IMU calibration.
     
  10. bizrank

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    Very interesting and helpful. Often I've had perfect flights even despite large negative readings at startup. What I've done is mentally added the negative value to the altitude reading when I get up high. Still, I wonder why that startup altitude reading is sometimes negative, sometimes right on the money?
     
  11. Mako79

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    Just a suggestion...
    Do an advanced IMU when the phantom is cold. Do it first thing when you plug it in the PC Phantom Assistance. The longer you leave the phantom on, the longer it will take to do the advanced IMU calibrations. If its too hot, it may not even complete the calibration. Make sure you remove the gimbal clamp when doing the calibration and do it on a level surface.
    The phantom without the props spinning heats up quickly, therefore the warmth will affect the barometric reading during calibrations.
     
  12. FreeFlyer

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    Hi guys... i noticed a similar problem with my phantom but, in my case, the values changes from about 0 to -1.5... i think that this is regular but, since i'm a newbie, i ask you to confirm that...

    I have a P2V+...

    (Sorry for bad english)
     
  13. Emmbee

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    Thanks for your informative and helpful comments.

    Much appreciated.
     
  14. M.Tigelaar

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  15. FreeFlyer

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  16. smaugnaut

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    This has been discussed before and there was no clear solution. I have settled for the fact that sometimes its right and sometimes its wrong. Usually power cycling everything 0's out for me. Calibration will never help you with this problem so dont waste your time. I have tested the v2+ rth when altitude was -40' and it works fine. It just sucks when you really want fly at a certain level over water and any other reason for accurate altitude.
     
  17. Emmbee

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    Tonight, when systems turned on but propellers not spinning, the altitude read -42 ft.
    This time I waited and waited and within about 10 minutes the altitude display gradually showed more or less the correct level.

    Turned all off and tried again, same result - do I have a very slow reacting Barometer ?
     
  18. Morgon

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    Since the IMU includes the barometer, could you have done your last IMU calibration when the unit was already warm?
    It sounds like the barometer is getting to the level you last calibrated it at after it's warmed up a bit.
     
  19. Adznz11

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    Is any one else experiencing large altitude variations in the p2v+? My model seems to go up and down in elevation alot. So much so that is unsafe to fly without eyes on it at all times especially at lower altitudes. This will not do for the Ariel action shooting i do as i need to be very reliant on fpv frame. It only started showing this problem after a hard landing along with quite a noticeable yaw drift. I have done alot of advanced calibrations even leveled of the NAZA unit it has tamed the yaw drift somewhat but not entirely like it was out of the box. However my main issue is with the altitude fluctuations. When landing close the ground some times it will yoyo violently near touch down. Hardly ideal. I have searched every where but no one seems to have had a similar problem with altitude hold as me. I am aware that it may be a problem with the barometer or barometer sensor but do not know if there is any way to address this bar replacing the naza entirely which i am reluctant to do. Has anyone ever experienced this phenomenon?
     
  20. Adznz11

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    I have even put my unit in the fridge prior to calibration in an attempt to get a more accurate barometric calibration but nothing seems to be changing the large variations in altitude. I want to start my own thread on this issue but it won't let me. Getting really frustrated becoming a nightmare. Surely one person must have or is experiencing this?