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IOSD mini calibration

Discussion in 'General Discussion' started by Hughie, Dec 26, 2014.

  1. Hughie

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    I have just fitted an IOSD mini to my P2 and noticed that after I turn on and let it initialise and set homepoint, the IOSD mini height indication flickers between 1/2 or 2/3 metres even though it is (obviously) on the ground.

    Now I can tell from the units that resolution of this metric is not that accurate, but I would have probably expected it to indictate 0m or 0/1 m.

    Is this normal, is there a way to reset this the same way one would do so with a nomal aeroplane barometric altimeter ?

    Does this error indicate that the height at which the quad thinks it is back on the ground is 6+feet out ? or does the Naza compute that from elsewhere?

    Thanks.
     
  2. sergekouper

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    I think the Data comes from the GPS which is known for not being accurate on Altitude information.
     
  3. noiseboy72

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    There is a barometric pressure sensor as well as GPS. Resetting the quadcopter by power cycling it is usually enough to get it to zero.
     
  4. The Editor

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    GPS altitude information is totally useless and cannot be relied upon - it is not unusual for the height reported to be +/- 400ft out!! :shock:
    The Naza/Phantom gets its height information from an on board barometer (with resolution of around 10cm) which feeds info to the iOsd/iOsd Mini. Although the initial reading may be a little off the barometer relies on change in height to 'calibrate' more accurately.
    The user cannot reset/calibrate the barometer in the Naza, it 'resets' each time the craft is powered up - that's why it reads zero(ish) irrespective of how high/low ASL you are.
     
  5. sergekouper

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  6. Hughie

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    Thanks to all who have responded.

    I already had elimiated this as being anything to do with GPS.

    I am told (unverified) that the transducer is a BMP085
    http://www.adafruit.com/datasheets/BMP0 ... ly2008.pdf

    It is told to sample and do an AtoD conversion to yield a value representing hPa.

    There is no reason why, if it knows it is on the ground during initialisation that the main controller cannot record this offset as being 0m AGL. It clearly is doing something odd.
     
  7. Hughie

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    So I had another flight today, and despite proper preflight checks the IOSD height still shows 6-8m when on the ground. I did an advanced IMU calibration yesterday. Recycling the power switch does not help. Otherwise, it flies normally, the only difference is that I have added the IOSD and can now see the flight parameters.

    Any ideas ?
    Thanks