I've seen debate in a few different threads about compass calibration and whether you should or shouldn't do it often.

I've got a Mavic Air.  I calibrate my compass anytime the app tells me to.  This happens about every few days.  I take off from different locations almost each time I fly.  I keep my MA with me all the time.  This means that it travels in the car a lot.  While in the case, it is obviously not turned on, and the battery is not installed.  I do not turn it on near the car.  Instead i only turn it on near the take off location (wherever that may be for the day).  I do wear a fitbit with a magnetic clasp.

Is there a problem with calibrating the compass before each flight?   I've seen people say that you shouldn't do that.  I'd like to understand why.  Is there such a thing as over-calibration?

Any clarification will help.

No such thing as over calibration. But if you already have a good compass then it is only possible to make it worse by calibration, you certainly won’t be able to make it better.
So yes if you are asked to calibrate do, but one thing you must watch out for is if app asks you to move aircraft or calibrate, it would be almost certainly wrong to calibrate in this spot and move is your safest option.
I would also say it’s not normal to have to calibrate so often, but I have to say sensors for compass in Mavic Air seem to be set to very sensitive so we have seen more requests to calibrate on this craft. I have it since it was first released and have had to calibrate twice and in this time I have flown many times hundreds or even thousands of miles away.

Mavic Air is equipped with a look up table that stores global information so no need unless requested to calibrate when traveling distance.

hallmark007 Posted at 2018-5-3 07:11
No such thing as over calibration. But if you already have a good compass then it is only possible to make it worse by calibration, you certainly won’t be able to make it better.
So yes if you are asked to calibrate do, but one thing you must watch out for is if app asks you to move aircraft or calibrate, it would be almost certainly wrong to calibrate in this spot and move is your safest option.
I would also say it’s not normal to have to calibrate so often, but I have to say sensors for compass in Mavic Air seem to be set to very sensitive so we have seen more requests to calibrate on this craft. I have it since it was first released and have had to calibrate twice and in this time I have flown many times hundreds or even thousands of miles away.

This makes sense.    I don't just calibrate for the sake of calibration.  I only calibrate when the app asks me to.  However, you made a good point.  some times it says calibrate or move to a different area.  In those times, i actually do both.  i try to move away from where i am at that moment, and then do the calibration.

Although I did have to re-calibrate when i launched from the park last weekend, most of my launches have been from paved areas.  I read in one of the posts debating this that rebar can cause the need to re-calibrate.  Is this true?

I mentioned that i keep it with me so it rides in the car a lot.  That (to this point) has only included my daily commute which keeps me in an area of about 100 sq miles.   It has yet to make an interstate travel, but that is coming very soon, so i'll be able to say that I've flown 1000 miles from home.  Normally though, i'll likely be in the local area just looking for parks and lakes and things to fly around.

A lot of people are actually complaining of having to calibrate, but it doesn't bother me.  It takes about 10 seconds, and then i can put the quad down and take off.  

Thanks for your response.

3-D Posted at 2018-5-3 07:36
This makes sense.    I don't just calibrate for the sake of calibration.  I only calibrate when the app asks me to.  However, you made a good point.  some times it says calibrate or move to a different area.  In those times, i actually do both.  i try to move away from where i am at that moment, and then do the calibration.

Although I did have to re-calibrate when i launched from the park last weekend, most of my launches have been from paved areas.  I read in one of the posts debating this that rebar can cause the need to re-calibrate.  Is this true?

Rebar is one of the most common causes for compass problems and your app will not always pick up on this. Once your drone is not turned on when traveling in the car, it will have no effect on compass.

I'm one of the people that have complained about constant compass calibration being required, although it didn't really bother me as like you say it takes 10 seconds and it's done (if it works 1st time).

However since I installed Litchi, neither Litchi nor DJI Go4 have asked me to calibrate (so far) and I have flown maybe 3 times up to now.

hallmark007 Posted at 2018-5-3 07:46
Rebar is one of the most common causes for compass problems and your app will not always pick up on this. Once your drone is not turned on when traveling in the car, it will have no effect on compass.

Thanks.  i'll keep this in mind

Robothamster Posted at 2018-5-3 07:49
I'm one of the people that have complained about constant compass calibration being required, although it didn't really bother me as like you say it takes 10 seconds and it's done (if it works 1st time).

However since I installed Litchi, neither Litchi nor DJI Go4 have asked me to calibrate (so far) and I have flown maybe 3 times up to now.

i have been hearing/reading a lot about Litchi.  I'm going to have to give it a try.  If only it would sync flight data/distance with the DJI Go app.  i like being able to keep up with that for the sake of knowing how much airtime i've accumulated.  Kinda like keeping up with the mileage on my car...

I've only calibrated when asked, or when traveling a long distance.

ImTravis Posted at 2018-5-3 08:21
I've only calibrated when asked, or when traveling a long distance.

how often are you asked to calibrate?

I calibrate my compass anytime the app tells me to.

When I first got my Mavic Pro P, virtually every single time I powered MPP, RC, and started GO-4; the system said drone needed compass calibration.
It did not matter where I calibrated compass at.  Even out in open field, that I knew at least 8-foot down there was no ferrous metals, the system said drone needed compass calibration.  

After a while, I started ignoring compass calibrate, because it was obvious a bug in system creating a false need for calibration.  The MPP's diretional compass would show correct direction, even when system was giving compass calibrate being needed.

When I switched to CrystalSky Ultra-brite, the false messages of compass needing calibration stopped.  When my first CS-Ub failed, and I was forced to go back to iPhone / iPad, suprisingly I did not get false compass calibration messages.  There had been at least one firmware update during that brief time.  Possibly GO 4 was updated for iPhone / iPad as well.

Since getting my replacement CrystalSky Ultra-brite back, I have not seen a compass calibration needed.  Even when flight locations have changed by over 100-miles.

3-D Posted at 2018-5-3 07:36
This makes sense.    I don't just calibrate for the sake of calibration.  I only calibrate when the app asks me to.  However, you made a good point.  some times it says calibrate or move to a different area.  In those times, i actually do both.  i try to move away from where i am at that moment, and then do the calibration.

Although I did have to re-calibrate when i launched from the park last weekend, most of my launches have been from paved areas.  I read in one of the posts debating this that rebar can cause the need to re-calibrate.  Is this true?

I read in one of the posts debating this that rebar can cause the need to re-calibrate.  Is this true?  

I originally believed that.  But that was when I was getting compass calibrations virtually everytime I went out to fly.  Not so sure now.
One of things that through me off with Compass calibrations, is messages were tied to what got powered cycled or restarted (Mavic, RC, iPhone, GO-4).

After getting my 2nd CrsytalSky U-b, I have flown several times from same large concrete pad area that has cattle panels (heavy-gauge metal wire in square pattern) in concrete, along with one 2-foot x 40-foot long area having rebar in concrete.   Thus far I have not gotten a message about Compass needing to be recalibrated.

I plan to do some more testing to see if I can trigger a Compass recalibrate.

HedgeTrimmer Posted at 2018-5-3 08:37
I calibrate my compass anytime the app tells me to.

When I first got my Mavic Pro P, virtually every single time I powered MPP, RC, and started GO-4; the system said drone needed compass calibration.

this seems to be a common thread...  Initially it asks for calibration, installed something else, go back , it stops asking...

anyone at DJI wanna comment?

Same thing here, but after doing  a new calibration  it was fine again :-)

I'm curious, would the metal ring on the outside of my foldable landing pad affect the compass?

I get asked for it on the Air pretty much every time I move location (i.e. every time I fly!), even for a few kms, hardly asked at all with the Pro!

I don' t believe any of the compass recalibration stuff. I very much doubt that somewhere inside this craft is a little magnetic needle floating in some water... They have made some changes in the new software. I bet it stops this request from being so frequent

Sometimes when I fire up, I get "bangs" from the app telling me to recalibrate compass, IMU etc.  But, if I reboot the AC, RC and smart phone, they go away.

Sometimes when I fire up, I get "bangs" from the app telling me to recalibrate compass, IMU etc.  But, if I reboot the AC, RC and smart phone, they go away.

I'm not officially sure if that's the right thing to do but I have not experienced any issues in doing so.

And as a side note, I seem to get the app "bangs" when I start the aircraft anywhere other than my takeoff spot.  Not sure if there's any science to that, just an observation.

Kevjones1959 Posted at 2018-5-4 05:02
I don' t believe any of the compass recalibration stuff. I very much doubt that somewhere inside this craft is a little magnetic needle floating in some water... They have made some changes in the new software. I bet it stops this request from being so frequent

Digital compass, but if you don’t heed warnings you could end up crashing into the water, then your compass will be floating about. ;+)<{<

3-D Posted at 2018-5-3 08:26
how often are you asked to calibrate?

I think I've been asked once. After that, haven't had to except when traveling long distances.

HedgeTrimmer Posted at 2018-5-3 08:52
I read in one of the posts debating this that rebar can cause the need to re-calibrate.  Is this true?  

I originally believed that.  But that was when I was getting compass calibrations virtually everytime I went out to fly.  Not so sure now.

HedgeTrimmer (myself): along with one 2-foot x 40-foot long area having rebar in concrete.    Thus far I have not gotten a message about Compass needing to be  recalibrated.

When I got to area today, I powered MPP up right in middle of 2-foot x 40-foot long area that has rebar, and also has plastic conduit with 240VAC running two-foot below concrete.

This time, I did get a Compass magnetic interference alert.  As I picked up MPP and started moving away, the Compass alert went away.  Moved back about 10-foot, putting MPP down on concrete with metal cattle panels.  No alerts, and MPP flew fine.

Was flying the other day in a scenic area with cement picnic tables. When MP was sitting on picnic table I got compass error. Had to move away to get a good reading. I'm sure I'm over cautious but If I am flying more than a mile from where I last flew I calibrate the compass. I have NEVER had a problem with my MP knowing where it is.

hallmark007 Posted at 2018-5-4 05:07
Digital compass, but if you don’t heed warnings you could end up crashing into the water, then your compass will be floating about. ;+)

ha ha

Here this video will explain compass problems calibration in dji aircraft.

cspain Posted at 2018-5-4 04:24
I'm curious, would the metal ring on the outside of my foldable landing pad affect the compass?

Good question.  
From my experience with two different sized foldable pads in open fields, no.
The large pad, with metal ring I do have with me is magnetic.  Don't know about smaller one.

What could happen, is a folding pad with metal (ferrous) ring, coupled with other ferrous metals might cause Magnetic Interference.   
But how to do a valid test is a problem:  
Pad alone - no problem.
Concrete with some rebar - no problem
Pad + Concrete with some rebar - problem

3-D Posted at 2018-5-3 08:26
how often are you asked to calibrate?

Every single time I power on the Air. Including after changing batteries in the same location.

SeanGalbraith Posted at 2018-5-6 09:44
Every single time I power on the Air. Including after changing batteries in the same location.

I'm not sure if the new firmware made a difference, but since I've updated, I haven't been required to calibrate at all.

3-D Posted at 2018-5-7 03:45
I'm not sure if the new firmware made a difference, but since I've updated, I haven't been required to calibrate at all.

Same here ..something has changed

hallmark007 Posted at 2018-5-5 08:04
Here this video will explain compass problems calibration in dji aircraft.

https://youtu.be/ZL6NbpzJVJI

@hallmark007 How does this guy know this???

Kevjones1959 Posted at 2018-5-7 07:58
@hallmark007 How does this guy know this???

There are many here who also know this, if you research and try through similar forums contact with RC engineers , and share the information. Some might say a bit geeky but others love to know what makes everything tick. I also think you will find this information very accurate and useful.

Funny enough, after the firmware update, my MA has been asking me to calibrate everytime i turn it on.

sstimeare Posted at 2018-5-7 09:40
Funny enough, after the firmware update, my MA has been asking me to calibrate everytime i turn it on.

yeah.  i've got the opposite effect.

hallmark007 Posted at 2018-5-7 08:18
There are many here who also know this, if you research and try through similar forums contact with RC engineers , and share the information. Some might say a bit geeky but others love to know what makes everything tick. I also think you will find this information very accurate and useful.

and I really appreciate that.

Also, I have problems with an excessive amount of messages about the need to re-calibrate the compass - before updates it was not - I think that these are system software errors. Previously I had a different error before the upgrade concerned the software of the camera - each time the drone was turned on, the camera set itself in the camera mode enabled the serial mode - after the update works correctly.
So - updates one fix other spoil. I apologize for my weak English language.

hallmark007 Posted at 2018-5-7 08:18
There are many here who also know this, if you research and try through similar forums contact with RC engineers , and share the information. Some might say a bit geeky but others love to know what makes everything tick. I also think you will find this information very accurate and useful.

@hallmark007, Hi bud, i fully understand his rational explanation of how the various systems function in general. I am tech savy enough to understand how GPS works etc, but the way this guy explains the interaction of the DJI implementation gives me  the impression that he is actually looking at the code.  look at his explanation for example on the flight mode drop down. It is not really possible to determine exactly how this is implemented unless you look at at code. So I guess I am asking if he has access to the code else he would of needed to fly in virtually every situation and document the actual behaviour.

Kevjones1959 Posted at 2018-5-8 07:08
@hallmark007, Hi bud, i fully understand his rational explanation of how the various systems function in general. I am tech savy enough to understand how GPS works etc, but the way this guy explains the interaction of the DJI implementation gives me  the impression that he is actually looking at the code.  look at his explanation for example on the flight mode drop down. It is not really possible to determine exactly how this is implemented unless you look at at code. So I guess I am asking if he has access to the code else he would of needed to fly in virtually every situation and document the actual behaviour.

There are a couple who I think have access to code, this guy is well connected so you could be right, but I can’t confirm but I will ask, can’t hurt to ask.

3-D Posted at 2018-5-7 03:45
I'm not sure if the new firmware made a difference, but since I've updated, I haven't been required to calibrate at all.

I've only been out once, and it required a calibration. I'll see if it requires it next time, and when I'm out long enough to need a battery change. Fingers crossed.

I haven't been asked to calibrate since I got the Air first week of March. Only asked to move the craft which I have done in all cases and the drone still fly's perfectly. But I think I should do one since it has gone through so many updates. But I am reluctant because I am a strong believer in not fixing something that isn't broken.

ANTHONYVLOG Posted at 2018-5-8 16:58
I haven't been asked to calibrate since I got the Air first week of March. Only asked to move the craft which I have done in all cases and the drone still fly's perfectly. But I think I should do one since it has gone through so many updates. But I am reluctant because I am a strong believer in not fixing something that isn't broken.

Well, unless the quad requests a calibration, I wouldn't do one.   It seems that the results are all over the place.  Some people always require it, some people almost never require it, and some people are somewhere in the middle.

I know that location, and a plethora of circumstances come into play,  but as an engineer, it's difficult to accept such wide ranging results.  I like things to be defined and structured and equal.
I'll just have to let this bounce around on the artist side of my brain, which doesn't really care about all that detail and symmetry.

Thanks to all who have given their input.  I appreciate it.  I'm really glad that the community is so open and willing to answer seemingly mundane questions.