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Compass Calibration, A Complete Primer

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

  1. ianwood

    ianwood Taco Wrangler
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    Why Calibrate?
    Compass calibration is important to safe, controlled flight. It compensates for changing background magnetic "noise", a.k.a. magnetic inclination and deviation (not to be confused with declination). Inclination and deviation that isn't corrected through compass calibration will cause inconsistencies between GPS and compass that can result in "toilet bowl effect", a swirling motion that can cause the Phantom to fly out of control.

    What is Magnetic Inclination and Deviation?
    Magnetic deviation is a horizontal variation that comes from the Phantom itself and the equipment you have installed on it as well as the magnetic makeup of the area you are flying in (again not to be confused with declination). Sometimes the deviation will be insignificant, but other times it can be big enough to cause you to lose control. Inclination is a vertical magnetic variation that shifts depending on where you are.

    Warning Signs
    The Phantom can only detect when the compass is providing extremely poor (implausible) data. This typically occurs if you place it near a strong magnetic field or do not calibrate it properly. It will flash red and yellow lights and the P3 will indicate a compass error in the app.

    IMPORTANT: The lack of a compass error does NOT mean your compass is working and calibrated properly.

    MOD Value
    This is the total magnetic field calculated using the "sum of squares" from the X, Y and Z axes. On the P2, you need to plug in the cable and use the assistant software. For the P3, you can see it in the app. It should be between 1,300 and 1,600, ideally just above 1,400. Check it away from magnetic influences. If it reads very high or very low, check it again in a different location. If it is still off, it could need calibration or it could be magnetized or damaged.

    IMPORTANT: A good mod value does NOT mean your compass is working and calibrated properly. For example, if you calibrate next to some rebar, your mod value may still be OK until you fly away from the rebar.

    What Does Calibration Actually Do?
    Calibration measures the magnetic fingerprint of the surrounding area. By turning the compass 360 degrees, the Phantom can see where the compass reading doesn't smoothly increase or decrease. It uses this information to build an adaption table so that when the Phantom turns during flight, the reading is smooth and linear.

    When Should I Calibrate?
    You do not need to calibrate before every flight and in some cases you definitely should not calibrate. That doesn't mean you shouldn't ever bother doing it. It only takes one time for it to go very wrong. The most important aspect of compass calibration is making sure the magnetic "neighborhood" around your Phantom is consistent between calibration and during flight.

    IMPORTANT: The ideal place to calibrate is an open field with nothing metallic in a 20ft radius. Keep away from drainage pipes, irrigation systems, rocks, etc.
    • DO Calibrate
      • Mod value out of whack or compass error reported (check area first).
      • Circling in flight (also check for other possible causes).
      • New equipment added or removed / new firmware installed.
      • Location change (greater than ~100 miles).
      • Significant change in terrain (e.g. to / from mountains).
      • If you just degaussed your compass (BTW, don't degauss unless instructed).
    • DO NOT Calibrate
      • If near concrete, buildings, and hidden or overhead power lines / pipes / etc.
      • If you're indoors, on a paved surface, on a stone surface, on the beach, on a boat, on a balcony, near a car, near speakers, etc.
      • If there are metallic (ferrous) objects nearby or you're not sure
    • Pre-Calibration Checklist
      • Everything used in flight should be powered during calibration, e.g. GoPro, tracker, etc.
      • Remove all metal from within 10ft radius, e.g. watch, phone, ring, belt, coins, controller.
      • Calibrate on grass or dirt and not on concrete, asphalt.
      • Calibrate on a level surface if possible.
      • A cardboard box is a good idea to get it off the ground and level.
    • How to Calibrate
      • Power up your Phantom and accessories as normal.
      • Wait until your Phantom is ready to fly.
      • P1 / P2: Flip S1 five times between the top two positions.
        P3: Select CALIBRATE under AIRCRAFT STATUS | COMPASS. Click OK.
      • Confirm solid yellow rear lights.
      • Pick up the Phantom and turn it smoothly and steadily a full 360 degrees until the lights turn solid green.
      • Point the front of the Phantom straight down and repeat until the lights turn off and resume normal flashing.
        Note: Don't be concerned if your gimbal reacts poorly to being face down, keep turning as normal.
      • Optional: power off and restart Phantom.
      • Enjoy your flight!
    If for any reason, you do not complete any of the above steps smoothly and evenly, restart the process.
     
    #1 ianwood, Jan 8, 2015
    Last edited: Oct 22, 2015
    Neon Euc, Squirrel!, Adam L and 43 others like this.
  2. Great Pumpkin

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    Excellent calibration primer, ianwood!
    Change What to Wait in the second line of your How to Calibrate.
    Then I have to ask: Why not calibrate on a beach?!?
     
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  3. Hughie

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    A really nice post. Thanks.
     
  4. phenom3030

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    Excellent post! Thanks for the information, it should be made a "sticky"!
     
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  5. Narrator

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    Great post.
    Surprised about the beach.
     
  6. turbodronepilot

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    Nice job ianwood..I appreciate the effort. ..
     
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  7. Happyflyer

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    Very nice.
    Same: The beach?
     
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  8. Larry L

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    Thank you. Great info. I too am interested why not at beach?????
     
  9. ianwood

    ianwood Taco Wrangler
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    Sand often has iron in it. Depends on where you are though. Sand also has the undesirable characteristic of getting everywhere, including into stators, between battery contacts, etc.
     
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  10. Great Pumpkin

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    ianwood, rare is the beach that has iron in it, and certainly not enough to cause compass calibration problems for a Phantom. I'm not thrilled about flying from a dry sandy beach, however, just because of the way sand can get into everything as you mentioned. I've flown many times from a wet sandy beach.
     
  11. Hughie

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    I think it might be something called magnetite which is the problem. And it isnt found in all beaches.
     
  12. John J.

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    Thanks for the beach info - I'll need to research this further - my phantom2/zenmuse gimbal/gopro hero4 I launched from a bluff above a beach in Punta Cana last week and flew beautifully for 10 minutes. I had calibrated since this was my first flight since leaving Canada. After hand-grabbing on return, we packed up and descended the bluff to the beach. Restarted DJI controller then Phantom per usual, once GPS locked I flew the Phantom along the beach 50 feet out over ocean, and 5 minutes later while returning for landing, she parked, hovered and slowly descended into the ocean. Salvaged footage here, thanks! : https://www.youtube.com/watch?v=03uLQ9uP-v8
     
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  13. ianwood

    ianwood Taco Wrangler
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    Yes, it's not all beaches but iron is present on a number of them. No idea what percentage. It depends where you are. If you know there's no ferrous material at your beach, go for it.
     
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  14. Buk

    Buk

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    Thank you Ian for this primer.

    One question. Please explain, in not too technical terms, adaption table.
     
  15. Larry L

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    Thanks for the beach info. I always take off from my case to eliminate as much interference from anything being in or on the ground
     
  16. michael.reynolds1775

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    Nice write up. I appreciate reading about basics and agree this should be a sticky!
     
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  17. phenom3030

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    Does anyone know what the raw data for the compass should be in the Assistant software? I came across this video recently and he says the "mod" number should be "1500"? Also numbers shouldn't be negative...

    Checked mine and its at around 1060. With a negative number on the X axis (-112).


    here's the link to the video:

    http://youtu.be/aqzYYDBkymM?list=PLSe7f2ltTl0XiP_pevju6ouUmhJx_sBaO
     
  18. Hughie

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    I was told by dji supplier in the UK that the mod should be between 1300 and 1600.
     
  19. Marlin009

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    Curious, why not a boat? Mine, in particular, has 5 batteries and it would be difficult to get more than 10' away from them.

    Is that the reason?
     
  20. sergekouper

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    Thanks Ian for this great post. Better than a sticky, I put it aside for future reference.