Compass Calibration curiosity

[Deleted member 94047]

So I know the MA prompts compass calibration if you have moved a certain distance from your last location. I traveled a bit this week and the MA asked for a compass calibration the first time I turned it on in the location I traveled to and my home upon my return. In both cases, the onscreen message was about magnetic interference (which there was none). I went through the logs today and it is clear that the MA knew why a compass calibration was needed

-158.507 : 1199 [L-COMPASS][mag_cali_pt] distance_from_last 77852.617 km|
-158.487 : 1200 [L-FMU/MOTOR]mag_need_action: cali mag
-158.147 : 1217 [L-FMU/LED]action changed. compass out of range:need_cali(1)

My first puzzle is why wouldn't the MA (or more precisely GO4) display a message that accurately reflects the reason for the calibration request? Something like "Compass needs calibration since you have moved too far from your last location" instead of (mis)informing me about a magnetic interference that doesn't exist? But this is a minor peeve.

Looking at the "distance_from_last" entry which triggered the calibration request, I see that it tells me I have traveled 77852.617 kms which I most certainly didn't. So I kept looking. I see that after a successful compass calibration, the MA stores the time and location details of the calibration point. There I see these entries.

-10.493 : 8619 [L-COMPASS][scale cali(0)] estimation error:[0.0]
-10.493 : 8619 [L-COMPASS][scale cali(0)] succeed! bias:5180.0 -1855.3 1875.3 scal:4.148 3.914 3.985|
-10.493 : 8619 [L-COMPASS][save data] app cali all success
-10.493 : 8619 [L-COMPASS][save data] in user index mode
-10.493 : 8619 [L-COMPASS]mag cali pos and time saved success!
-10.493 : 8619 [L-COMPASS][mag_cali_pt]lat:0.202431, lon:0.653067
-10.493 : 8619 [L-COMPASS][mag_cali_pt]height:1819.3, date:20190915

Now that entry in red is clearly wrong if it is logging the location of the calibration site. If you care to know where that is, it is in the middle of the Atlantic ocean here

I checked the location entry of the other calibration site as well. It is near to the other entry above.

-45.023 : 6023 [L-COMPASS][scale cali(0)] estimation error:[35.0]
-45.023 : 6023 [L-COMPASS][scale cali(0)] succeed! bias:5095.4 -1805.8 1890.2 scal:4.048 3.867 3.967|
-45.023 : 6023 [L-COMPASS][save data] app cali all success
-45.023 : 6023 [L-COMPASS][save data] in user index mode
-45.023 : 6023 [L-COMPASS]mag cali pos and time saved success!
-45.023 : 6023 [L-COMPASS][mag_cali_pt]lat:0.193397, lon:0.644666
-45.023 : 6023 [L-COMPASS][mag_cali_pt]height:2428.2, date:20190911
-45.023 : 6023 [L-COMPASS]req gimbal recover when cali end
-44.923 : 6028 [L-FMU/LED]action changed. Normal Flash(0)

Clearly, the MA knows where it is as it updated and saved its home point location soon after the calibration. Hence I thought this "[L-COMPASS][mag_cali_pt]" location entry could be a reference entry in its look up table (I remember reading it does have a lookup table somewhere). So could this be a reference point in the table? Or is my MA indeed thinking the compass was calibrated in the middle of the Atlantic Ocean and hence why it thinks I moved 77852.617 kms from the last calibration location?

Puzzled!

 

[brass_monkey]

Hmm..the circumference of the earth at the equator is around 40000 km. So nowhere on earth can be more than 20000 km from anywhere else on earth. I can't see any way that 77000+ km can be true no matter where it thinks that you last calibrated it.

 

[Deleted member 94047]

Hmm..the circumference of the earth at the equator is around 40000 km. So nowhere on earth can be more than 20000 km from anywhere else on earth. I can't see any way that 77000+ km can be true no matter where it thinks that you last calibrated it.

Didn't even think about that, good catch! So, bogus data or DatCon misreading the log?

 

[sar104]

Hmm..the circumference of the earth at the equator is around 40000 km. So nowhere on earth can be more than 20000 km from anywhere else on earth. I can't see any way that 77000+ km can be true no matter where it thinks that you last calibrated it.

It's mislabeled - the units are meters.

 

[sar104]

So I know the MA prompts compass calibration if you have moved a certain distance from your last location. I traveled a bit this week and the MA asked for a compass calibration the first time I turned it on in the location I traveled to and my home upon my return. In both cases, the onscreen message was about magnetic interference (which there was none). I went through the logs today and it is clear that the MA knew why a compass calibration was needed


My first puzzle is why wouldn't the MA (or more precisely GO4) display a message that accurately reflects the reason for the calibration request? Something like "Compass needs calibration since you have moved too far from your last location" instead of (mis)informing me about a magnetic interference that doesn't exist? But this is a minor peeve.

Looking at the "distance_from_last" entry which triggered the calibration request, I see that it tells me I have traveled 77852.617 kms which I most certainly didn't. So I kept looking. I see that after a successful compass calibration, the MA stores the time and location details of the calibration point. There I see these entries.



Now that entry in red is clearly wrong if it is logging the location of the calibration site. If you care to know where that is, it is in the middle of the Atlantic ocean here

I checked the location entry of the other calibration site as well. It is near to the other entry above.


Clearly, the MA knows where it is as it updated and saved its home point location soon after the calibration. Hence I thought this "[L-COMPASS][mag_cali_pt]" location entry could be a reference entry in its look up table (I remember reading it does have a lookup table somewhere). So could this be a reference point in the table? Or is my MA indeed thinking the compass was calibrated in the middle of the Atlantic Ocean and hence why it thinks I moved 77852.617 kms from the last calibration location?

Puzzled!

Lat/long is in radians, not degrees. That's 11.59844° N, 37.41798° E.

 

[Deleted member 94047]

Thanks @sar104; curiosity quenched. And that's my home alright

 

[brett8883]

What would we do without @sar104 ?

 

[tck444]

My similar experience. Seems every time I try to fly, the calibration is required ? Quite annoying !

Just showing a friend how it flies, and taking 10 minutes to get the thing in the air !

 

[Deleted member 94047]

On the contrary, mine is quite well behaved in this regard. Never asks me for a calibration if I haven't moved somewhere else or sometime has passed since my last calibration. I was just puzzled by the entries in the log regarding last location of calibration and distance from it. Sar was kind enough to explain it to me.

 

[Peio64270]

I don't understand why compass calibration is so often required by some drones. Practically, calibration just takes into account internal interferences or strong magnetic perturbations just in the vicinity (by vicinity, I mean centimeters). I own 2 Phantoms 3, one Mavic pro and various analogic and digital compasses in my boat. Non of these never asked me for a calibration since the initial one except once : when I tried to take off with a P3 from a garden metallic table. I moved some meters away and the warning disappeared. However I travelled thousands miles with all this material...

 

[DanMan32]

The only reason I can come up with is because the Air and M2 are prone to get magnetized when stored near magnets such as speakers. As long as the residual magnetism is low, compass calibration can compensate.

 

[sar104]

I don't understand why compass calibration is so often required by some drones. Practically, calibration just takes into account internal interferences or strong magnetic perturbations just in the vicinity (by vicinity, I mean centimeters). I own 2 Phantoms 3, one Mavic pro and various analogic and digital compasses in my boat. Non of these never asked me for a calibration since the initial one except once : when I tried to take off with a P3 from a garden metallic table. I moved some meters away and the warning disappeared. However I travelled thousands miles with all this material...

Just to clarify - the calibration doesn't correct for any magnetic fields that are not produced by the aircraft itself. Internal fields only.

 

[hiflyer201]

Who knows why the air is so persistent about compass calibration. Sunday I flew three times in the middle of the Mojave desert. I didn’t change launch points one inch and the second flight required a compass calibration. I’ve changed countries with my Spark and not been requested to Calibrate.
I figured that it was just acting like a drone ?

 

[Peio64270]

Just to clarify - the calibration doesn't correct for any magnetic fields that are not produced by the aircraft itself. Internal fields only.

Yes, this is what I said substancially. Thus it can be very hazardous to calibrate regularly since the risk is to calibrate in a bad magnetic environment and to be exposed to discrepancies between GPS and compass data once in flight.
But my basic question remains : "why are some drones asking so often for compass calibration ?"

 

[Nakita Mosquita]

Changing locations significantly (ie flying in Kaui versus flying in Ontario) prompts calibration. I've had my MA for one year now and remain uncertain of the 'proper' way to perform the calibration.
1. Does the direction of the rotation matter?
2. When tilting the drone on it's side, during the 2nd part of the calibration, some illustrations show the camera pointing horizontally, while some show the camera pointing down. Does it matter? Which is correct?

 

[sar104]

Changing locations significantly (ie flying in Kaui versus flying in Ontario) prompts calibration. I've had my MA for one year now and remain uncertain of the 'proper' way to perform the calibration.
1. Does the direction of the rotation matter?
2. When tilting the drone on it's side, during the 2nd part of the calibration, some illustrations show the camera pointing horizontally, while some show the camera pointing down. Does it matter? Which is correct?

There are definitely inconsistencies between the on-screen and instruction manual procedures for several models. The axis of rotation doesn't seem to matter as long as it is rotated 360° around two approximately orthogonal axes.

 

[Nakita Mosquita]

Agreed. Camera facing down or not on 2nd part of calibration?

 

[sar104]

Agreed. Camera facing down or not on 2nd part of calibration?

Both work.

 

[Nakita Mosquita]

Thanks Sars.