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Compass Calibration, A Complete Primer

Discussion in 'General Discussion' started by ianwood, Jan 8, 2015.

  1. Tsyrawe

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    I don't understand why Phantom uses such an unreliable device as a compass. GPS and a gyro should be enough to define and maintain orientation in space.
     
  2. sonof40

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    I believe it's to indicate the direction your camera is pointing.
     
  3. Ken Hanks

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    GPS can only show your heading while aircraft is in motion, hence the need for a compass.
     
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  4. Tsyrawe

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    Sure, I know that. But this method would be simpler than relying on the magnetic field. A drone would calibrate "the compass" by itself. What's more, while flying a drone would be able to adjust "the compass" constantly.

    Another thing:
    A simple solution to fly-aways caused by erroneus GPS reading would be monitoring by the software sudden changes of drone's position. When the software sees such a sudden change it could, for instance stop, a drone and wait for next readings. Somebody mentioned such s solution already.
     
  5. ianwood

    ianwood Taco Wrangler

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    It actually does do some level of adaption in flight on an ongoing basis. However, that becomes tricky due to wind.
     
  6. Fat City

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    The compass is essential for flying indoors where GPS signals are generally not available. Another potential issue with GPS is the frequency of new position fixes. It may be different now, but years ago GPS chip sets calculated position only once per second, and this is way too slow to control yaw.
     
  7. Tsyrawe

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    Wind shoold not be a factor. Two or one giros and GPS would do the trick.
     
  8. Tsyrawe

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    Once set is set. Gyros would keep the orientation in space. A check every second or even a couple of seconds would be enough.
     
  9. ianwood

    ianwood Taco Wrangler

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    The phantom doesn't use the old fashioned single axis gyros. It uses a 3 axis MEMs gyro and a 3 axis MEMs accelerometer. But that has little if anything to do with the compass adaption. They can help but only so much.

    In order to adapt the compass purely, you need to derive a heading adaption from the course over ground. If the course over ground is effected by the wind (which it is), you can only trust it so much. You can probably improve confidence if the reciprocal shows something different than a 180 difference in course over ground but it is not exact.

    The real issue with sensor fusion, which is what we are talking about, is when one sensor goes rogue. Adapting compass values automatically from other sensors is fine right up until they drift or experience noise or other factors that can cause the whole thing to go wonky very quickly.
     
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  10. Wolfiesden

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    Rofl! I know how it feels. I tend to react poorly when I am face down too. Ooooh room's spinning. Someone stop the room, I want to get off.

    Anyway, thanks for the great tips! Really appreciate the time you put into documenting all that.
     
  11. Wolfiesden

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    Just curious, whats on the transom of your boat? If its not a wooden paddle and its a big metal thing called a motor, don't you think being only 10' away from that magnetic thing could affect the compass? I would also think that the rocking of the boat during the calibration might also sway the calibration results.
     
  12. P3Pdancer

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    I have metal staples in my stomach from weight loss surgery. No idea how much or what kind of metal. Does that likely make me a walking No Calibration Zone?

    I also have a Dental partial plate that its made of metal. But a megnet is not attracted to it. So it's out safe to assume that I can leave my teeth in during calibration?
     
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  13. msinger

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    P3Pdancer, when holding the Phantom, extend yours arms straight out and you should be fine.
     
  14. Fat City

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    I think any metal implanted or attached to your body for medical purposes has to be non-magnetic to be compatible with MRI scanners.
    But there can be magnets that you could forget about. For example, I wear glasses that have tiny neodymium magnets in the temples that hold sunglasses. Some tablets and cellphones have magnets built-in or added as part of a mounting system, many electric cases have magnetic closures, etc.
    Luckily the force of a small magnets field is inversely proportional to the cube of its. distance.
     
  15. Tsyrawe

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    How it is in case of really big drones or, for that matter, airplanes? One has to do the same dance to satisfy the compass?
     
  16. LSZ1318

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    Sorry but I need to see jpgs of that awesomeness.
     
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  17. Aurelien

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    Thanks for a great article!


    Sent from my iPhone using PhantomPilots mobile app
     
    ianwood likes this.
  18. Mutterranch

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    Great article.
    You said calibrating in volcanic areas in not a good thing, How and where should a person calibrate his compass on Maui? I'm hoping to fly there in November.
     
  19. Meta4

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    You should be able to find plenty of suitable areas for calibrating your compass on Maui.
    Just not close to any active volcanic areas.
     
  20. Mutterranch

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    I misunderstood. I don't think I'll be near any ACTIVE volcanoes.
    Thanks
     
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