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Why is a compass calibration needed?
1812 29 2018-6-28
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Rblomqvist
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So probably a very basic question, but I'm new to drones and still lots to learn


From time to time I'm asked to do a compass calibration on my MA. My question is why this is required if my location has not changed?  

I totally get a compass calibration is needed if you move location as the strength and direction of magnetic fields changes etc. But shouldn't that value be stored in MA and be referenced to when it starts? And unless the GPS show you have moved x distance it will go back to the stored value even if there are interference? In other words, what is causing the built in compass to require a calibration? I get that you should have no interference as you are performing the calibration but why is it required after all when it had a good compass reading already stored?

Same is true with the IMU?




  

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hallmark007
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It’s the six million dollar question, but the setting asking for compass to be calibrated seems to be set very sensitive. You really should never need to calibrate compass, and yes MavAir is the first dji consumer drone with a look up table , to alert you if your in an area of magnetic declination.

Calibration gives the compass the information it needs to determine which magnetic influences are part of the Mavic and what is the earth's normal magnetic field.
The compass doesn't lose calibration and doesn't ever need re-calibration unless you add or remove equipment to/from the Mavic, or move to an area with changing declination.

So this is the only answer I can give you now, hopefully dji will see some sense and lighten up a bit on this, many are having to calibrate every time they fly.
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3-D
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There will likely be some very scientific answers, but my simple answer is this:
The MA actually does a system check when you power it on, and verifies compass calibration as part of that system check.  I've found that it if i'm moving toward the location where I want to launch, and I turn the MA on while in motion, it asks me for compass calibration.  If i'm still, and already in the location, and I simply turn it on and put it down, I don't get that prompt.  There are lots of factors that can change the compass calibration.  Some of them major, (like taking off near a car  or on concrete with rebar underneath, and some as simple as the device wasn't able to get a lock when it tried to.

As I said, very unscientific, but for my purposes, and my experience, it answered my question.  Once I figured this out, for the next 30 flights, I only had to calibrate 1 time.
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Rblomqvist
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hallmark007 Posted at 2018-6-28 10:57
It’s the six million dollar question, but the setting asking for compass to be calibrated seems to be set very sensitive. You really should never need to calibrate compass, and yes MavAir is the first dji consumer drone with a look up table , to alert you if your in an area of magnetic declination.

Calibration gives the compass the information it needs to determine which magnetic influences are part of the Mavic and what is the earth's normal magnetic field.

Thanks for the reply hallmark007, then it is not just me not understanding.
Sounds DJI for some, most likely good reason, have made the compass very sensitive.
With all reported issues with yaw etc, perhaps it comes down to the threshold/sensitivity setting in fw is the root cause?   
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hallmark007
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Rblomqvist Posted at 2018-6-28 11:07
Thanks for the reply hallmark007, then it is not just me not understanding.
Sounds DJI for some, most likely good reason, have made the compass very sensitive.
With all reported issues with yaw etc, perhaps it comes down to the threshold/sensitivity setting in fw is the root cause?

Your understanding is quite correct, and BTW this is the only dji drone this happens on.
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3-D
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Rblomqvist Posted at 2018-6-28 11:07
Thanks for the reply hallmark007, then it is not just me not understanding.
Sounds DJI for some, most likely good reason, have made the compass very sensitive.
With all reported issues with yaw etc, perhaps it comes down to the threshold/sensitivity setting in fw is the root cause?

I'm one of the ones that agrees that firmware has caused some issues.  However, I don't think this is one of them.  

No, it's not just you not understanding.  It is a very real phenomenon.    But I won't put this one on the firmware.  This is something else entirely.
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Rblomqvist
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3-D Posted at 2018-6-28 11:13
I'm one of the ones that agrees that firmware has caused some issues.  However, I don't think this is one of them.  

No, it's not just you not understanding.  It is a very real phenomenon.    But I won't put this one on the firmware.  This is something else entirely.

Thanks 3-D,
Can you please explain more why you don't believe the fw has anything to do with this?
If DJI made some code changes around the compass, this could explain why some owners experience the .0400 fw was the starting point for their problems? If the MA does have issues with the compass (=require calibration) during boot, what will ensure it won't happen while in flight? I have no clue about the vendor(s) of the magnetometer, but perhaps they have different batches, some more sensitive than others?     
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Rockbyter
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With my Mavic Pro I notice that the calibration is now different.  Used to be upright and then nose down but is now upright then on it's side for compass calibration.  Anyone know if it matters which side it is put on when I do the compass dance?
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3-D
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The only reason that i don't believe this particular issue is FW related is because this was an issue for me prior to the firmware update.  Once i got it corrected, it was no longer an issue.  It did not come back for me after the firmware update.  I did suffer the yaw problem as well as the active track/attack problem.  I also suffered from the connectivity and distance reduction problem.  those are all things that i attributed to the firmware.  My compass problems were pre .0400.  That is just my personal experience.  I can't say for certain if there were any compass changes in the code because DJI is terrible at change documentation, so we may never know what the code actually changed.
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HedgeTrimmer
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If it makes you feel any better, it is not only Mavic Air, seen these with Mavic Pro.  

I used to get repeated Compass calibrations with my Mavic Pro: Repeated Compass Recalibrate warnings.  

Repeated compass calibrations got so bad, I would do one for that day of flying, and for rest of day of flying, I ignored any more warnings.

I believe its a False warning that has something to do with GO-4 and what SmartDevice GO-4 is running on, thus version of GO-4.  Once I switched from iPhone 5s and iPad 2(?), over to CrystalSky (which runs a different version of GO-4); compass re-calibration warnings abruptly stopped.
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hallmark007
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Rblomqvist Posted at 2018-6-28 11:29
Thanks 3-D,
Can you please explain more why you don't believe the fw has anything to do with this?
If DJI made some code changes around the compass, this could explain why some owners experience the .0400 fw was the starting point for their problems? If the MA does have issues with the compass (=require calibration) during boot, what will ensure it won't happen while in flight? I have no clue about the vendor(s) of the magnetometer, but perhaps they have different batches, some more sensitive than others?

I think you will find there is only one person on that thread with calibration problem, I have owned a Mavic Pro for almost two years have never been asked to calibrate, and you will find it hard to find any other threads with similar problems with aircraft asking for calibration. But it is common place on MavAir forum.
However I have now seen some similar on the new P4Pro 2.
It’s not a false warning, simply because your aircraft won’t take off unless you calibrate.
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3-D
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Rockbyter Posted at 2018-6-28 11:34
With my Mavic Pro I notice that the calibration is now different.  Used to be upright and then nose down but is now upright then on it's side for compass calibration.  Anyone know if it matters which side it is put on when I do the compass dance?

The MA is the same.  And apparently it doesn't matter because I didn't notice it until someone mentioned it, and I had calibrated mine with the nose down.
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HedgeTrimmer
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what is causing the built in compass to require a calibration?


Next time you get a compass calibration request, take a look at Sensor state for compass.  See what Mavic Air's compass sensors are showing in regards to Interference.
Assuming no sources of magnetic interference nearby, and compass sensor's were correctly calibrated last time, the Bar should be Green.  I would expect value for sensor state to be lower than 150.  On my Mavic Pro two compass sensor states are usually below 50.


Here is how to access sensor state for compass (at least with GO-4 running on CrystalSky)

* Under main menu of GO-4 App - in middle at Top of Screen - Tap on QuadCopter Icon
  * At bottom of MC Settings screen - Tap on Adance Settings
  * At bottom of Advance Settings screen - Tap on Sensor State
  * At top of Sensor State screen - Tap on Compass
  
  Below Interference, one compass for Mavic Air, you should see two compasses forMavic Pro.
In case of Mavic Pro, Blue dot next to Compass (1 or 2) indicates which one is being used

Screen snapshot from GO-4 for Mavic Pro.




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hallmark007
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Rblomqvist Posted at 2018-6-28 11:29
Thanks 3-D,
Can you please explain more why you don't believe the fw has anything to do with this?
If DJI made some code changes around the compass, this could explain why some owners experience the .0400 fw was the starting point for their problems? If the MA does have issues with the compass (=require calibration) during boot, what will ensure it won't happen while in flight? I have no clue about the vendor(s) of the magnetometer, but perhaps they have different batches, some more sensitive than others?

Its been there since day one here’s an early thread, https://forum.dji.com/forum.php? ... &fromuid=260008

So if it Firmware then it was in original firmware, there are lots of these threads.
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hallmark007
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Rblomqvist Posted at 2018-6-28 11:29
Thanks 3-D,
Can you please explain more why you don't believe the fw has anything to do with this?
If DJI made some code changes around the compass, this could explain why some owners experience the .0400 fw was the starting point for their problems? If the MA does have issues with the compass (=require calibration) during boot, what will ensure it won't happen while in flight? I have no clue about the vendor(s) of the magnetometer, but perhaps they have different batches, some more sensitive than others?

Its been there since day one here’s an early thread, https://forum.dji.com/forum.php? ... &fromuid=260008

So if it Firmware then it was in original firmware, there are lots of these threads.
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Robothamster
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I still have to calibrate compass 8/10 times I turn the Air on.  

It's easy enough to do, but wish it wasn't as frequent.  My Spark I only ever had to do it once.

I'm always careful to be still when I turn on, away from any metal objects (inc concrete in case of rebar) and don't wear smart watch.  I'm wondering if maybe my S8 is anything to do with it?
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Bokepacha
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Robothamster Posted at 2018-6-29 01:19
I still have to calibrate compass 8/10 times I turn the Air on.  

It's easy enough to do, but wish it wasn't as frequent.  My Spark I only ever had to do it once.

When I started with the MA, I use to be requested to calibrate almost every time. Then I realized I was ALWAYS turning on the drone close to metallic stuff (my bike, a car, metallic stairs, etc.). After that, I always try to turn it on at least at 2 meters from any metallic object and so far I haven't had any request for recalibration.
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Robothamster
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Bokepacha Posted at 2018-6-29 01:34
When I started with the MA, I use to be requested to calibrate almost every time. Then I realized I was ALWAYS turning on the drone close to metallic stuff (my bike, a car, metallic stairs, etc.). After that, I always try to turn it on at least at 2 meters from any metallic object and so far I haven't had any request for recalibration.

I too turn it on well away from metal objects but makes no difference.  

I wear a fully titanium watch (non magnetic), so that or the S8 phone are only things with metal in them.
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gnirtS
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gnirtS
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Because it knows nothing about the environment around you.  It doesn't know is value stored is "good" (note thats not the same as interference).  If there is interference it can't take off despite a stored value - it simply wont know which direction is which.  The EM characteristics of a position can change in the space of a few feet as well (metallic rocks, buried cables, mobile phones with magnetic cases in pockets, cars etc) and even change for an identical location.Storing the device next to an EM field can also cause changes in the compass internally which means it needs recalibration.

IMU is fine, its good without further reclibration unless its had a bump, is damaged and so on.

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msinger
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Rockbyter Posted at 2018-6-28 11:34
With my Mavic Pro I notice that the calibration is now different.  Used to be upright and then nose down but is now upright then on it's side for compass calibration.  Anyone know if it matters which side it is put on when I do the compass dance?

It's okay to calibrate the compass either way.
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Aardvark
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My belief is that the compass does not need to be calibrated unless you are prompted by the system to do so. I also believe that the calibration is done so that a slight bias or offset can be added to the compass reading to allow for the affect of any metal or electromagnetic interference generated by the aircraft itself. My thought would be the same for a standard magnetic compass, it does not need calibrating as you change location. But if you clipped it to your map with a bulldog clip (proof of concept) then I would expect to have to make an allowance for that, I would offset the bezel as required to indicate the true reading.

I have never been prompted to update the compass on my P4 or Mavic Pro at take off point. If you get a notification to calibrate with the aircraft sitting at take off point and clear of any obvious interference. The first thing to try is move to a new location.

Or in similar fashion the magnetic ships compass, with 'Kelvins Balls' (sic) to offset the effects of the ships ironwork. As seen Here
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gnirtS
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Well ships analogue compasses have magnetic deviation due to the metalwork and electrical items and that deviation isnt a a simply offset, it varies depending on the compass heading.  Thats why you need a table or a graph (after someone has worked it out for that compass in that location on that boat) to determine the correct compass indicated heading.
All electrical compasses need calibrating.
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hallmark007
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Aardvark Posted at 2018-6-29 02:10
My belief is that the compass does not need to be calibrated unless you are prompted by the system to do so. I also believe that the calibration is done so that a slight bias or offset can be added to the compass reading to allow for the affect of any metal or electromagnetic interference generated by the aircraft itself. My thought would be the same for a standard magnetic compass, it does not need calibrating as you change location. But if you clipped it to your map with a bulldog clip (proof of concept) then I would expect to have to make an allowance for that, I would offset the bezel as required to indicate the true reading.

I have never been prompted to update the compass on my P4 or Mavic Pro at take off point. If you get a notification to calibrate with the aircraft sitting at take off point and clear of any obvious interference. The first thing to try is move to a new location.

While I agree with what you say , and I believe the OP does as well, however the problem he speaks of seems to be inherent to Mavic Air , in that it continually asks to be calibrated, you can check compass values find them ok, move your aircraft, but you will only be able to take off your aircraft if you preform compass calibration.
I also have owned Mavic Pro for almost two years and have never been asked to calibrate and similar with my other drones.
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Robothamster
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hallmark007 Posted at 2018-6-29 03:23
While I agree with what you say , and I believe the OP does as well, however the problem he speaks of seems to be inherent to Mavic Air , in that it continually asks to be calibrated, you can check compass values find them ok, move your aircraft, but you will only be able to take off your aircraft if you preform compass calibration.
I also have owned Mavic Pro for almost two years and have never been asked to calibrate and similar with my other drones.

Exactly.

It's almost like the compass calibration is a little too sensitive in the Air.  As I said earlier, my  Spark only asked for compass calibration once in maybe 30 flights (then sold it) and I'm not doing anything differently with the Air but it's *almost* every flight in a new location (if I'm swapping batteries in same place it never asks).

I don't mind doing the calibration most of the time, better safe than sorry.  But it's a bit concerning that mine needs it a lot and some other people find they don't need to do it.  Also, I had one time in France near a waterfall where it wanted calibration and I tried 5 times and the calibration failed each time so I had to abandon flying it there which was a real shame as it was an amazing location.
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hallmark007
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Robothamster Posted at 2018-6-29 03:57
Exactly.

It's almost like the compass calibration is a little too sensitive in the Air.  As I said earlier, my  Spark only asked for compass calibration once in maybe 30 flights (then sold it) and I'm not doing anything differently with the Air but it's *almost* every flight in a new location (if I'm swapping batteries in same place it never asks).

Yes I have had a situation where it became very trying to calibrate, eventually switched all off back on and managed it then. Hopefully a software/firmware update may help with this.
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Aardvark
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hallmark007 Posted at 2018-6-29 03:23
While I agree with what you say , and I believe the OP does as well, however the problem he speaks of seems to be inherent to Mavic Air , in that it continually asks to be calibrated, you can check compass values find them ok, move your aircraft, but you will only be able to take off your aircraft if you preform compass calibration.
I also have owned Mavic Pro for almost two years and have never been asked to calibrate and similar with my other drones.

Yes, agreed, I've seen one or two reports that suggest a problem where 'calibration required' seems wrongly reported, which would point towards Application or maybe firmware/hardware conflict.
I'd misunderstood that this was the problem here. I do get messages flagged up when aircraft is powered up and close to a source of disturbance, the screws in my wooden desk as one example, and thought that might be the case here.

My reply was focused more on the 'change location', and 'magnetic field changes'. Change of location should not require a calibration.

As a thought does the aircraft status indicator show a calibration required when reported by the App' ?

Edit:- I wonder if DJI have programmed this as a 'feature' in the Mavic Air :-)

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HedgeTrimmer
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What happened to simply send it in vs. continuing to wait for next firmware release to possibly fix it?
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hallmark007
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Aardvark Posted at 2018-6-29 04:23
Yes, agreed, I've seen one or two reports that suggest a problem where 'calibration required' seems wrongly reported, which would point towards Application or maybe firmware/hardware conflict.
I'd misunderstood that this was the problem here. I do get messages flagged up when aircraft is powered up and close to a source of disturbance, the screws in my wooden desk as one example, and thought that might be the case here.

Yes it does show, I had thought that it was purposely set by dji, to force in to calibrating, but for some it happens on every flight, some even when they change battery.
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KayvinM
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When I first got the MA I went through a month and half with no issues or requests by the app to do a compass calibration. Then suddenly I've been having to do it every 2 weeks or so no matter how many times I fly in between. Now I don't know if this has anything to do with it but during that month and half with no issues I was using my Nexus 9 (which is a recommended device) . The issues started to appear as soon as I began using the Galaxy Tab S2(which I bought specifically for the MA). Every time I get the request to calibrate I check the compass values and they are all in the green or good state but the only way I can take off is if I calibrate the compass.  I'm no expert but It seems like to much of a coincidence that my issues started happening shortly after I started to use the Galaxy tab. I'll try and use the Nexus 9 again and see if it I get another calibration request 2 weeks from now.
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