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elevation altitude of home reads incorrectly

Discussion in 'Phantom 2 Vision + Discussion' started by sheldrake, Jun 2, 2014.

  1. sheldrake

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    I know that the elevation of where I take off from and land is 182 feet, but my 2 + always displays between 70 and 8o feet. I always calibrate compass before each flight. Can anybody tell me what I should do ? The return to home function works - i have tested it.
     
  2. SilentAV8R

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    The displayed elevation is relative to the ground level of the starting point. It is above ground elevation (agl), not the actual elevation of your flying site plus the elevation above the ground.
     
  3. N017RW

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    Additionally, the o/b barometer it is not compensated for temperature and pressure.
     
  4. sheldrake

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    The actual elevation of the ground where phantom lifts off is 180. The FPV display reads 70 feet. What am i missing ? I dont understand previous comments. Any advice would be appreciated
     
  5. SilentAV8R

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    The display is telling you how far you are above the ground where you took off.

    AGL = Above Ground Level

    Your physical altitude is 180 feet Mean Sea Level (MSL). 70 feet AGL would be 250 feet MSL.

    The Phantom altimeter displays the AGL and NOT the MSL value
     
  6. N017RW

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    Altitude is determined by air pressure.

    Air pressure is dependent not only on altitude, but on factors such as temperature, relative humidity, and weather conditions.
     
  7. sheldrake

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    phantom displays 70 feet when sitting on the ground, not after taking off
     
  8. SilentAV8R

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    Ah, now I see!! This was not clear from your first post. It should read closer to zero. I am located at 480 feet MSL and fly at several locations that range from sea level to 900 feet MSL or so. Mine always reads at, or near, zero when it starts up.

    Have you let it sit for a time to see if it adjusts itself? If so, and it is still off, then it appears that there may be something blocking the small port that allows the barometric sensor to establish the base altitude pressure.
     
  9. sheldrake

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    yes i have let it sit for a complete battery cycle with no change. where is the port located?
     
  10. SilentAV8R

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    That I cannot tell you because I am not certain. It may also be a bad sensor. SOrry I cannot tell you more.
     
  11. N017RW

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    What is the elevation change between your IMU calibration location and your flying location?
     
  12. sheldrake

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    Not sure what you mean by IMU calibaration number. I am a newbie. I have only done the regular compass calibrations and the RC calibration. Is there another calibration that i should perform?
     
  13. N017RW

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    Yes, the calibration of the Phantom or better said the IMU.

    There is already tons of info published about this so I won't repeat but just search Google or You Tube for video tutorials of the 'DJI Phantom IMU calibration' or similar.
     
  14. sheldrake

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    Thank you, I have watched all the vids. but none of them mention altitude. Does that matter?
     
  15. Flyer91

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    There is no way to calibrate the altimeter.
    You need to send it back as defective.
    The "Return To Home" altitude that defaults to 60' AGL will be significantly off if you are reading 70' AGL on the ground.
    That will not be good if you go into fail-safe or (after activating Naza) you do an RTH, when you are erroneously reading 70'AGL at take-off.
    If it fail-safes, or you select RTH when you are below 60', your Plus will fly to 10' below the take off point and then (assuming it survived the 'up to' 10' of digging) try to burrow it's way home.
     
  16. sar104

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    I don't think that the IMU calibration affects the barometric sensor, which simply reads differential atmospheric pressure. As mentioned, it is supposed to be relative to take-off (power on) point, so if it reads significantly non-zero at power on then that suggests a faulty sensor. On take-off and climb, does the reading increase appropriately?
     
  17. N017RW

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    Correct, you won't find any mention of altitude during calibration.

    HOWEVER...The IMU contains: a 3-axis accelerometer, a 3-axis angular velocity meter and a barometric altimeter.

    Therefore it is not a stretch that during IMU calibration the barometer is zeroed in a similar fashion to the accel. and velocity sensors.

    If so, this might contribute to the error you are experiencing.
     
  18. sheldrake

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    here is the strange thing I forgot to mention - i have done 5 RTH, and all of them went flawlessly. My RTH waypoint sits at 180 feet above sea levl and slowly descends to 30 feet above sea level in a distance of .6 miles and then another 4 miles until it hits the Atlantic ocean
     
  19. Flyer91

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    Nope ...... unfortunately there's no calibration for the altimeter/barometric sensor.
    I had one that read + to - 60 feet on the ground, and DJI California said to return it to my dealer, as there is no calibration for it.
    It either works properly and reads within a few feet, or it's gone Elvis.
     
  20. Flyer91

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    It might be adding the 60 ' min RTH alt to the error it sees at take off.
    If at/above that total indicated height it will ..... or at least should, alt hold until overhead then descend and land.