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P3 Pro altimeter vs sonar reading off by 30FT

Discussion in 'Pro/Adv Discussion' started by ilgarm, Apr 5, 2016.

  1. ilgarm

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    Has anyone experienced 30+ FT altitude difference on P3 Pro when comparing sonar vs altimeter?
    During initial take off all good but when you go fly around and come back to a sonar altitude, altimeter reads higher (as high as 30FT sometimes).
    I contacted DJI support and their recommendation was to do compass calibration, which didn't make sense technically, and I do regular compass calibration anyways.
    See attached picture.
    Is this normal?

    IMG_0037.jpg
     
  2. exit 4

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    My P3A is off every time I fly. I never trust the altimeter. Never trust it when setting waypoints, always give yourself room for error setting waypoints.
     
    #2 exit 4, Apr 5, 2016
    Last edited: Apr 5, 2016
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  3. flpholt

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    my p3a is the same
     
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  4. Meta4

    Meta4 Moderator
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    No ... it's not normal and it is a safety issue if you are trusting the altitude reading.
    If DJI help suggested a compass calibration to fix this, they don't know what they are talking about.
    The compass is important but is 100% unrelated to altitude.

    The altitude sensor is a barometer measuring air pressure.
    It's part of the IMU and recalibrating the IMU will often fix this sort of error.
    Do it indoors on a perfectly level surface.

    You may still see small errors due to temperature change during a flight but they should be much smaller, like 1-2 metres.
     
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  5. SCGENE

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    mine P3A started this today at 3ft it showed 19ft and I let grandson fly it and he said 461ft and I asked distance and he said NO height, so I took radio and went above 500ft, what happen to 400ft max. P3A has the current firmware and also started NO Signal (video)
    The P4 not exceeding 400.
     
  6. Meta4

    Meta4 Moderator
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    The P3 & P4 can fly to 500 metres above your launch point.
    There is the ability to set a maximum height in the app if you want to limit it.
     
  7. SCGENE

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    They have always been set at 500 meters but they have always max out at 394 ft. and would go any higher, I don't care to exceed 400ft but I was thinking the 400ft was written in the firmware.
     
  8. yakangler10

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    I've experienced this on my P3P and found it strange so your not alone.
     
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  9. Meta4

    Meta4 Moderator
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    You are not setting it correctly - There is no firmware limit of 400 feet.
    The limit is stored in the Phantom so you have to have the Phantom connected to change the setting.
    If you set it correctly any P3 or P4 will fly to 500 metres above launch point.
     
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  10. Trackman1

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    A cold IMU calibration helped my altitude. Before calibration the p3 would land at 20ft. Now it is 7ft.
     
  11. ilgarm

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    Well cold IMU calibration seems to have worked for now.
    Now I get -1 to +4 FT difference in altimeter vs sonar readings. thanks to everyone for your comments.
    I wish I knew about this before I hit a palm tree which cost me $750 in repairs a month ago.
    Looking at the DJI app logs, altimeter was showing that I was supposed to be at 50FT but ended up hitting a tree which is barely 30FT tall.
    Is there a way to claim these damages from DJI? Did anyone succeed in getting DJI's attention for similar claims and how did you do it? ;-)
     
  12. With The Birds

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    Compass cal hey? Are you sure you called Dji? 30 ft error at flight end doesn't surprise me.... I have had similar. As said above, alt is taken from barometric pressure reading by an internal sensor. Warm air is less dense so reading will equate to alt being higher than actual, air pressure (atmosphere) is greater at sea level. Bird heats up alt reading off. I had 30ft plus error after performing a cold I I cal (bird fresh out of refrigerator). Recal at higher temp (close to flying ave) and I'm close to 5ft max error now.