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DJI Vision App and Compass Calibration...

Discussion in 'Phantom 2 Vision + Discussion' started by houstonpilot, Dec 27, 2014.

  1. houstonpilot

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    Everything I have read says to recalibrate the compass before starting a flight. In the DJI Vision app on my smartphone, I see a little compass on the bottom left with an arrow that points in the direction of the nose of the Phantom. If this compass is lining up with the Phantom, is calibration still necessary? If so, why?

    Also, prior to taking off, if the distance parameter in the APP is at 0 (or close to 0), is that sufficient confirmation that it has properly recorded it's take-off point as "home"?
     
  2. paulajayne

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    Calibration is required as the magnetic deviation will vary from place to place - buildings, power lines - soil all will affect it. So yes follow the manual.
    Home - make sure that you have a GPS lock prior to starting engines - Again follow the manual.
     
  3. JDNC

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    Is the calibration of the Phantom based on magnetic north and if so, should the cell phone compass be set also on magnetic north? I assume the compass displayed on the Ground Station map is indicating magnetic north? Confused as usual.
     
  4. houstonpilot

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    The app has an arrow that will literally show the direction of the nose of the phantom. Regarding home, even with a GPS lock, it's possible home is set at a different location. The point I was making is that one way to verify that the take-off location is properly registered as home is to make sure the "distance" parameter is set to zero on take-off.
     
  5. Meta4

    Meta4 Moderator
    Staff Member

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    That's not what the manual says.
    The manual says IMPORTANT: make sure to calibrate the compass in every new flight location - nothing at all about before every every flight. But DJI don't specify what constitutes a different location. As you'd expect, DJI are being very conservative and you can travel 100 km or more and still fly safely without recalibration. I (and many other flyers here) have tested this extensively.
    You do not need to calibrate every flight and to do so introduces the possibility of getting a bad calibration when you already had a good one.
     
  6. PhilD13

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    I would generally say if your about 25 +/- miles from the last point where it was calibrated then do it again before flight. If you walked down the street or went a few miles to the park in town or a field out of town then not really necessary unless you think the calibration may have been messed up by a magnetic field.

    The calibration uses a magnetometer to determine the direction of a magnetic field which varies depending upon where your located at the time. It then allows the controller to base position of the nose in relation to Magnetic North. So the controller will know the degree orientation of the nose from north.
    What happens if the drone thinks it's pointing south due to some kind of miscalibration but it actually pointed north? Lets say the GPS reports drift in the northern direction, but now the drone will try to move forward (remember it's still actually facing north). This creates positive feedback loop, causing the drone to rapidly increase power and resulting in a flyaway.
     
  7. ianwood

    ianwood Taco Wrangler
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    Calibration looks for nonlinear changes in the magnetic field due to localized magnetic influences aka deviation (not to be confused with declination). Generally, under 100 miles, there shouldn't be much change. But say within 20 miles you go from prairie to mountainous, you should recalibrate as there will likely be a different magnetic deviation between the two areas.

    When the compass and the GPS disagree, the result is TBE. The Naza computes a course to achieve a desired GPS position. It uses the compass to fly in the desired direction. If the compass is off, the Phantom will miss the target. The Naza will then recompute a new course to the desired target. Rinse, lather, repeat until you get a big circle. If the compass is off by a lot, the TBE can grow and eventually cause a flyaway.