Compass Calibration, A Complete Primer

ianwood

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#1
UPDATED October 2018

Why Calibrate?
Compass calibration is an essential part of flying. Bad compass data will cause a disagreement between the GPS and compass. Calibration corrects for magnetic deviation (NOT to be confused with declination) which is often responsible for generating bad compass data.

SIGNS OF A COMPASS PROBLEM
  • You get a compass warning. Duh!
  • The drone stops using P GPS mode and reverts to ATTI mode.
  • The drone flies in a circular pattern known as toilet bowl effect.
  • If the horizon in your image is rolling left and right like a cargo ship in a storm.
  • Your drone flies like it is drunk.
NOTE: The absence of a compass warning does not mean your compass is OK.

What Does Calibration Actually Do?
Calibration measures the magnetic fingerprint of the surrounding area and on your drone itself. By turning the compass 360 degrees in two different planes, the Phantom can see where the compass reading is not linear and adjust for it.

NOTE: When calibrating, it is essential that the magnetic environment on the drone and the area immediately around it is the same as when you fly it.

When Should I Calibrate?
You do not need to calibrate before every flight and in many cases you definitely should not. The most important aspect of compass calibration is making sure the magnetic environment around your drone is consistent between calibration and flight.

IMPORTANT: The ideal place to calibrate is an open field with nothing metallic in a 20ft radius or more (including above and below). Keep away from drainage pipes, irrigation systems, rocks, etc.

DO CALIBRATE IF...
  • You get a compass warning (check that you are not taking off from a magnet e.g. granite, car, etc.)
  • Your compass reading looks bad and you know there is nothing interfering on the ground.
  • You added or removed something metallic to the drone or have changed firmware.
  • You are far away from where you last calibrated (250 miles or more is a good benchmark).
  • Significant change in terrain (e.g. from grassland to mountains).

DO NOT CALIBRATE...
  • Before every flight. This is both unnecessary and risky.
  • If near concrete, buildings, and hidden or overhead power lines / pipes / etc.
  • Indoors, paved surfaces, stone surfaces, the beach, a boat, a balcony, near a car, near speakers, etc.
  • If there are metallic (ferrous) objects nearby or even if you're not sure.

Pre-Calibration Checklist
Everything used in flight should be powered during calibration, e.g. GoPro, tracker, etc.
Remove all metal within 15-20ft, e.g. watch, phone, ring, belt, coins, controller. Yes, your belt even!
Calibrate on grass or dirt and not on concrete, asphalt.
Calibrate on a level surface if possible.

How to calibrate
I've made this guide generic so it will apply to all DJI drones. Follow the steps in your app and/or user manual. It's pretty simple. It is important that once you are done, do a quick check of the compass reading and conduct a quick test flight. If you're not happy, you can do another calibration and re-test.


UBER NERDY / OLD STUFF:

What is Magnetic 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. If for any reason, you do not complete any of the above steps smoothly and evenly, restart the process.

MOD Value (P2 only)
DJI did away with this. 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 1,450. 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. The P4, P4P, Inspire 2 and newer models shows it as the difference from the ideal MOD value. It is the absolute value of the the ideal MOD value minus the current value e.g. ABS(1450 - MOD). The bigger the number, the more it is off.

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.
 
Last edited:
Joined
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#10
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.
 
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#12
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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ianwood

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#13
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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#17
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
 
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#18
phenom3030 said:
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
I was told by dji supplier in the UK that the mod should be between 1300 and 1600.
 

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