Compass Calibration Guide

[AYA74]

Hi Msinger. It looks like you know well about compass calibration. Can you please check at my following thread and let me know if you think this is normal to have the compass 2 always in red what the compass 1 one is moving from green to red (and vise versa) depending on the location? I have been unable to fly since I received my Mavic 3 days again and waiting for DJI to advise me the next step.
Mavic compass failed to calibrate
http://mavicpilots.com/index.php?threads/Mavic-compass-failed-to-calibrate.1335/



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[msinger]

It looks like one of your compasses needs to be replaced. I see DJI support is already working with you in their forum.

 

[rt60]

Why not calibrate on a beach? Minerals in the sand or something?

 

[raberrio]

please pin this thread thanks!

 

[Victor]

I wouldn't hold your breath on Galileo - they will not make their planned 30 orbital by 2020, they are already years late and billions over budget.
Oh , and so far, not enough satellites have been ordered to even reach the proposed 30. That doesn't include the three that are already faulty (and probably will need replacing)
We will all be flying Mavic 20's by the time the constellation is of any use - that is, if the EU don't scrap it and leave it up there as Space junk.

Sorry - a bit off topic.

Possibly, but at least they started a few more a few days back. (Long story cut short, I use to work at one of the control centres (GSOC) which has a dedicated Galileo control building)

 

[The Editor]

Possibly, but at least they started a few more a few days back. (Long story cut short, I use to work at one of the control centres (GSOC) which has a dedicated Galileo control building)

I hope you weren't made redundant - that's a bad sign!

 

[Andrew F]

So I live on Oahu, Hawaii, and it sounds like I calibrate once in a large open field, and I don't have to do it again unless prompted or flying in the mountains? The radius of the island is approximately 20 miles.

Aloha! I'll be flying in Olowalu. We should meet in between. Haha.

 

[raberrio]

Ok well yesterday was my first flight. Right out of the box, the aircraft asked me for compass calibration but no imu calibration. So i did what the aircraft wanted to.

The flight was ok but i still have the doubt if i have to calibrate the imu or not.

 

[BlooGoose]

I just started getting a message "Compass 1 Disconnected" and I cannot fly. Can someone help with what might be causing this and how to fix? Can someone tell me where the the two compass sensors are located within the Mavic? Thanks in advance.

 

[ThorDar]

I wouldn't hold your breath on Galileo - they will not make their planned 30 orbital by 2020, they are already years late and billions over budget.
Oh , and so far, not enough satellites have been ordered to even reach the proposed 30. That doesn't include the three that are already faulty (and probably will need replacing)
We will all be flying Mavic 20's by the time the constellation is of any use - that is, if the EU don't scrap it and leave it up there as Space junk.

Sorry - a bit off topic.

I don't know. Looks like they're starting to make some headway:

Constellation Information | European GNSS Service Centre

 

[AlanTheBeast]

For GPS satellites the (orbital) inclination angle is 55º and for Galileo the planned inclination angle is 56º. This means in practice that no satellites signals are received in the zenith direction north of the corresponding latitudes (i.e. north of 55º and 56º N). If the GNSS receiver is located further north, the elevation angles of the satellites is reduced as the latitude increases.

Which doesn't matter all that much. At any given time there are no GPS sats over your head no matter where you are. And when it occurs it is brief. (ie: As I write this, the coverage of sats for Hawaii is only marginally better than at the north pole).

Even at the north pole there are sufficient sats in view, at a high enough elevation that the altitude determination remains very good. And as you go to the north (from the US), then sats over Europe and Russia come into view.

One fly in the ointment is that at very high latitudes in the north the GPS will not receive WAAS or EGNOS differential corrections. (I'm not sure if Mavic even uses SBAS ... but if it did, then very far north would be near impossible ... and the coverage data is not for that region in any case.)

 

[Helo]

Which doesn't matter all that much. At any given time there are no GPS sats over your head no matter where you are. And when it occurs it is brief. (ie: As I write this, the coverage of sats for Hawaii is only marginally better than at the north pole).

Even at the north pole there are sufficient sats in view, at a high enough elevation that the altitude determination remains very good. And as you go to the north (from the US), then sats over Europe and Russia come into view.

One fly in the ointment is that at very high latitudes in the north the GPS will not receive WAAS or EGNOS differential corrections. (I'm not sure if Mavic even uses SBAS ... but if it did, then very far north would be near impossible ... and the coverage data is not for that region in any case.)

The constellations that make up GPS systems are not geosynchronous (they are not stationary) this is why when you stay in one position for a long period you will see your position plotted at random points around your original position. GPS positioning relies on triangulation so it looks for satellites that give you the best geometry and calculates you position. The best is 4 satellites, one directly overhead and three spaced 120° apart 20 to 30° above the horizon. The lack of satellites directly overhead in the Arctic does not mean there is no coverage but the altitude reporting suffers. A lot of the degradation of the signal is because of atmospheric interference in that area. I would guess this is the main culprit in the bad behavior of the Mavic.

There are two north's, True north (the north pole) and magnetic north (the point to which magnetic particles are attracted to). Having spent a summer flying helicopters north of the Arctic Circle (prior to GPS) I can tell you your compass is next to worthless and if you can't read a topo map your sol.

 

[AlanTheBeast]

The constellations that make up GPS systems are not geosynchronous (they are not stationary) this is why when you stay in one position for a long period you will see your position plotted at random points around your original position. GPS positioning relies on triangulation so it looks for satellites that give you the best geometry and calculates you position. The best is 4 satellites, one directly overhead and three spaced 120° apart 20 to 30° above the horizon. The lack of satellites directly overhead in the Arctic does not mean there is no coverage but the altitude reporting suffers. A lot of the degradation of the signal is because of atmospheric interference in that area. I would guess this is the main culprit in the bad behavior of the Mavic.

There are two north's, True north (the north pole) and magnetic north (the point to which magnetic particles are attracted to). Having spent a summer flying helicopters north of the Arctic Circle (prior to GPS) I can tell you your compass is next to worthless and if you can't read a topo map your sol.

I never said it was geosynchronous, did I?

When I said "at the time I was writing this" about Hawaii that was the "real time state": Over Hawaii at that time, there were no satellites there. Indeed the disbursement of satellites at Hawaii at that time was pretty much identical to the north pole with Hawaii having a slightly (slightly) better coverage.

Yes, this is ever changing. But the point is that the north pole is well served by satellites - it just never gets them vertically obviously.

The advantage to the GPS position is that horizontally it's actually quite damned good at the north pole. The vertical suffers a little bit - but not enough to worry about.

 

[AlanTheBeast]

GPS positioning relies on triangulation so it looks for satellites that give you the best geometry and calculates you position.

Ouch! No, GPS definitely does not rely on triangulation. Since the receiver cannot measure the angle to the satellite, it cannot triangulate.

What it measures is the time of arrival of the signals from the satellite. Since all satellites broadcast time references at the exact same time, the signal arrives at different times based on the distance of the receiver to the satellite. The receiver also receives the orbital data from each satellite and so with accurate time can compute the position in cartesean coordinates (centre of the earth) and thence spherical (lat/long/alt).

(You say you're a pilot? So this would be like RNAV using DME-DME-DME except instead of circles it's spheres). This is called tri-lateration or more properly multi-lateration.

When a GPS receiver shows you the azimuth and elevation to a satellite it is computed (not measured).

The GPS uses all the valid ranges (these are called pseudo ranges) to calculate an "over determined" position. Satellites below 10° are usually rejected (came through too much atmosphere). All the rest are used (unless flagged unhealthy of course).

Aviation receivers use RAIM to reject any PR's that are obviously wrong (don't fit the consensus position).

I don't know precisely if Mavic uses SBAS (WAAS) - but that would not work well in the arctic for sure. Likewise EGNOS which (IIRC) carries both GPS and GLONASS corrections. That is because the WAAS (or EGNOS) transmitters are on geosynchronous sats (commercial) and definitely do not reach the polar regions well.

 

[Helo]

Ouch! No, GPS definitely does not rely on triangulation. Since the receiver cannot measure the angle to the satellite, it cannot triangulate.

What it measures is the time of arrival of the signals from the satellite. Since all satellites broadcast time references at the exact same time, the signal arrives at different times based on the distance of the receiver to the satellite. The receiver also receives the orbital data from each satellite and so with accurate time can compute the position in cartesean coordinates (centre of the earth) and thence spherical (lat/long/alt).

(You say you're a pilot? So this would be like RNAV using DME-DME-DME except instead of circles it's spheres). This is called tri-lateration or more properly multi-lateration.

When a GPS receiver shows you the azimuth and elevation to a satellite it is computed (not measured).

The GPS uses all the valid ranges (these are called pseudo ranges) to calculate an "over determined" position. Satellites below 10° are usually rejected (came through too much atmosphere). All the rest are used (unless flagged unhealthy of course).

Aviation receivers use RAIM to reject any PR's that are obviously wrong (don't fit the consensus position).

I don't know precisely if Mavic uses SBAS (WAAS) - but that would not work well in the arctic for sure. Likewise EGNOS which (IIRC) carries both GPS and GLONASS corrections. That is because the WAAS (or EGNOS) transmitters are on geosynchronous sats (commercial) and definitely do not reach the polar regions well.

Peace AlanTheBeast. The purpose of my reply was to explain the workings of the gps system to people who may not be familiar with how it works without getting to technical, not to attack your post.

When I said "relying on triangulation" I was referring to the position of the satellites related to each other. You said compute, I said calculate. You supplied an excellent explanation of how they use that to find your position. You obviously know much more about the technical aspects to it.

I think we are both on the same page, so were good?

 

[jerryflah]

here is very good 30 seconds video of Mavic compass calibration

How To Calibrate The Compass On The DJI Mavic Like A Pro - YouTube

That's what I need VISUAL

 

[AlanTheBeast]

There was/is no war. I just react to things that don't make sense. You say you want to "explain the workings of GPS" w/o getting technical ... but triangulation is ... technical.

There is no triangulation and whether you say compute or calculate is the same thing in the end. The correct term is tri (or better multi) lateration because it's all about distances from sats to receivers. Angles are a computed (or calculated) afterthought so we can have a relative idea of where the sats are from our POV. Not to be pedantic. Uh ... well, ok, yeah, it is!

Cheers.

 

[AlanTheBeast]

That's what I need VISUAL

I like that. But I'd tend to simply turn it in place (not turn around) and same thing for vertical.

In the video he takes his time and the movement is smooth overall. I'd bet that doing it all over a long number of seconds (at least 5 - 10 for each axe like in the video) allows the processor to sample enough to make a proper table (or curve or whatever it really does).

At least the status light liked it!

 

[Strafe1]

Wow...someone got butt hurt! React is one thing. OVER react is another. Just relax.....

 

[jointeffort]

Why Calibrate?
Compass calibration is important to safe, controlled flight. It compensates for changing background magnetic "noise", a.k.a. magnetic inclination and deviation. 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 Mavic to fly out of control.

What is Magnetic Inclination and Deviation?
Magnetic deviation is a horizontal variation that comes from the Mavic 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 Mavic 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 Mavic 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.

Compass Interference
You can view the current compass interference in the "Main Controller Settings" --> "Advanced Settings" --> "Sensors" section of DJI GO. The colored bars should be in the green (Excellent) range when the Mavic is in a location that is away from magnetic influences. If the bars are in the red (Poor) range or close to it, move the Mavic to a different location and check again. If the compass interference is still in the red (Poor) range or close to it, the compass could need calibrated or it could be magnetized/damaged.

IMPORTANT: A good compass interference value does NOT mean your compass is working and calibrated properly. For example, if you calibrate next to some rebar, the compass interference might report good values 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 Mavic 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 Mavic 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 Mavic is consistent between calibration and during flight.

IMPORTANT: The ideal place to calibrate is an open field with nothing metallic in a 20 ft radius. Keep away from drainage pipes, irrigation systems, rocks, etc.

• DO Calibrate
  • Compass interference values are out of whack or compass error is 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 magnetic metallic objects nearby or you're not sure

• Pre-Calibration Checklist
  • Everything used in flight should be powered during calibration (e.g. GPS tracker).
  • Remove all metal from within 10 ft radius (e.g. watch, phone, ring, belt, coins, controller).
  • Calibrate on grass or dirt and not on concrete/asphalt (unless you know the concrete/asphalt does not contain rebar).
  • Calibrate on a level surface if possible.

• How to Calibrate
  • Power up your Mavic and accessories as normal.
  • Wait until your Mavic is ready to fly.
  • Select CALIBRATE under AIRCRAFT STATUS | COMPASS. Click OK.
  • Confirm solid yellow rear lights.
  • Pick up the Mavic and turn it smoothly and steadily a full 360 degrees until the lights turn solid green.
  • Point the front of the Mavic 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.

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

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Note: A lot of this information was copied over from ianwood's thread in the Phantom Pilots forum.

Thanks for this.


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