Compass Calibration, A Complete Primer

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#82
I am a new P3P user and very much appreciate your post. Thank you!


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#83
I have had my P3 Pro for about 9 months now. I usually calibrate the compass every time I fly in a different area. Do I not need to do this???
 
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#85
I did, That's why I was asking. Great info. The last calibration I did was in an asphalt parking lot at an Industrial Warehouse and it went flawless. I think I'm gonna just hit the field across the street now and do another calibration and leave it at that.
 
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#87
So, you're wondering if the info in the first post is accurate/trustworthy?
Not at all. Just confirming that it does not need to be done every time!
I have seen other posts on other forums (including this one) that said it should be done everytime you fly in a different location!
 
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#89
Right. And, the DJI manual says to calibrate before every flight.
That's what I have always done. Sometimes it's a hassle..especially on a construction site to find a good place to calibrate. Makes me feel a lot better knowing now that I don't have to do this every time!
 
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#92
Much appreciated; finally a concise and definitive post on this. Although I do think there might be an issue with P3A firmware recently as have had apparent compass issues every flight. New P3A to now fly and will start off by following this advice.
 
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#93
I was recently in the Pyrenees, lots of rust coloured boulders, they even mined for iron there in the past. I picked my compass calibration location very carefully indeed... Likewise, would magnetite in a sandy beach discolour the sand in a similar manner?
 
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#94
I was recently in the Pyrenees, lots of rust coloured boulders, they even mined for iron there in the past. I picked my compass calibration location very carefully indeed... Likewise, would magnetite in a sandy beach discolour the sand in a similar manner?
Nope, because the sand is being constantly turned over so the oxidation over time that turns it red is not present. 1 minute into the video it goes into oxidation and shows the difference between the oxidized red and the still black or washed black sands. As long as the black sand stays out of the water it will rust and turn red :)

 
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#95
I have a marine/aviation background, and would never be without a well calibrated compass. It is a great backup for the other far more complex systems. My boat compass requires a 360 degree rotation to calibrate, and in addition to finding magnetic north at that position, it calibrates out the changes on the other points of the compass. The dead simple marine compasses require a mechanical process - rotating left right and front back shafts to compensate for the compass point non-linearities. It is not a problem with a poorly made compass, but the net effect of the location, the boat's equipment etc.

Logging those settings over time establishes pretty clearly that 5 degree variations occurr routinely, and calibration gets rid of most of the errors.

Deriving heading, from the GPS as others have mentioned, works only if the Phantom is moving. This, if there is a side wind, is not the direction the ac is pointing, but rather the direction of travel, which is the vector combination of the heading and the wind offset. A further complication is the intrinsic error in the GPS position,which Can be up to 16 feet, and still be in spec.

DJI has created a very sophisticated and interdependent system, which uses gyros, gps, and compass, all working independently, and integrates these readings into a combination that works extremely well. Nobody has any control of the factors that impact the individual sensor systems errors. The systems job is to use all of the independent sensor data to arrive at a best guess of the truth.

Pilots and captains do this in their heads, based on their training and experience.


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#96
Nope, because the sand is being constantly turned over so the oxidation over time that turns it red is not present. 1 minute into the video it goes into oxidation and shows the difference between the oxidized red and the still black or washed black sands. As long as the black sand stays out of the water it will rust and turn red :)

Just a thought, if you dug up wet sand above the high tide level, and it was not stained brown then there is no iron in it? It would be exposed to salt water and oxygen, but not disturbed, so ideal conditions for oxidation. Come to think of it, any wet sand that's undisturbed and not discoloured must not contain iron?
 
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#97
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.
Excellent post.
 
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#98
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.
Having issues with my new out of the box Mavic. IMU calibrates fine. Compass will calibrate horizontally but not vertically nose down. Always magnetic interference. Have tried several times, restarted everything several times as well. Quite frustrating.
 
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So, are you saying that even when the DJI GO 4 App says "Compass Calibration Required" we shouldn't calibrate the compass?
 

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