There’s no fool like an old fool...Mavic Mini lost!!

[sar104]

Ah, I see your mistake now.

You are forgetting that the purpose of determining the drone's magnetic field is to adjust what the sensors see in total, and correctly determine where magnetic north is.

N = F - D
where N = magnetic north, F equals total field sensed, D equals the field of the drone. Okay, not mathematically that simple perhaps, but conceptually representative.

If you start your drone up, and it detects that north isn't where it should be (by comparing to GPS information?), then it knows something has changed.

Either F has changed, or D has changed. Or both.

YOU know D hasn't changed, but the drone does not until it calibrates again.

And that is why I believe the environment can trigger a request to recalibrate.

It "fixes" the problem of the drone not knowing what has changed.

The aircraft cannot "detect that north isn't where it should be" by comparing to GPS data, because GPS data have no direction information. As a result, your suggestion that this situation could trigger a recalibration request is wrong.

 

[old man mavic]

@sar104 with respect may i ask you a question ,about my method of using a compass to set my take off mat to north,and how that equates to having the drone arrow icon, in the radar like display, showing the drone facing the small n on the circle of the display, if i don't do that and just put it facing any direction then it does not face the n on the screen
i have held the belief that it was important to have the drone pointing to mag north before take off to allow everything in the operating system to have the correct orientation so the mavic can have a successful flight and i have done this and have never had any issues if you think this is wrong then i will not mention it again,as i would not want to misinform others on the forum thanks OMM

 

[sar104]

@sar104 with respect may i ask you a question ,about my method of using a compass to set my take off mat to north,and how that equates to having the drone arrow icon, in the radar like display, showing the drone facing the small n on the circle of the display, if i don't do that and just put it facing any direction then it does not face the n on the screen
i have held the belief that it was important to have the drone pointing to mag north before take off to allow everything in the operating system to have the correct orientation so the mavic can have a successful flight and i have done this and have never had any issues if you think this is wrong then i will not mention it again,as i would not want to misinform others on the forum thanks OMM

It's important that the aircraft orientation arrow is pointing in the right direction on the display. I do the same as you - I set the mat cardinal points on the ground with a compass so that I can compare the aircraft on the mat with the orientation arrow on the compass rose on the screen. But you can orient the aircraft on the map in any direction and then perform that check - the aircraft doesn't need to be facing north to start up correctly. Does that answer your question, or did I misunderstand?

 

[EricJT]

It's important that the aircraft orientation arrow is pointing in the right direction on the display. I do the same as you - I set the mat cardinal points on the ground with a compass so that I can compare the aircraft on the mat with the orientation arrow on the compass rose on the screen. But you can orient the aircraft on the map in any direction and then perform that check - the aircraft doesn't need to be facing north to start up correctly. Does that answer your question, or did I misunderstand?

So if the AC on the RC map inlay is indeed pointing in the same direction as the AC itself on the takeoff mat, it is good to go?

 

[sar104]

So if the AC on the RC map inlay is indeed pointing in the same direction as the AC itself on the takeoff mat, it is good to go?

Exactly - that means that the IMU yaw value has been correctly initialized.

 

[Peio64270]

Since you are finding the concept difficult to grasp, I'll try a different tack.

In a past life, before the days of GPS, I lived aboard and cruised on a yacht like this one:

(...)

You are definitely a very patient and didactic person

To add my little piece of work to what you said in your analogy, I still own and sail a such sailing yacht which is equiped with an autopilot.
This autopilot has its own compass and IMU (both in 2D only if I compare to those of my drones). These electronic sensors have to be placed in the center of the boat in order to be as less as possible disturbed by pitch and roll. The only convenient "center" location was in my boat a locker into which I told everybody not to store any piece of metal of any kind.
The compass calibration of the pilot is to be performed once in the autopilot life, just after installation instead you refit the boat. I did it carefully by circling regularly with the boat exactly the same way as the horizontal calibration of drone compass (but with a bit larger circles ) and I didn't think anymore in it for years though the boat travelled thousands nautical milles.
One day, however, I swiched in the pilot on a chosen route and I had the bad surprise to see the boat yawing brutally and making almost an half turn.
I didn't imagine that the compass needed a fresh calibration. Instead I went at the locker to look whether any magnetic object could have been stored in the vicinity of the compass. There were none but when I opened the adjacent locker, I discovered that it was full of food cans. I moved these cans away in an other locker and the autopilot got back to normal.
Any compass calibration under these conditions would have worked at the moment, I suppose, but then it would have likely produced a strange behaviour when the neighboring locker had been progressively emptied for kitchen needs...

 

[old man mavic]

It's important that the aircraft orientation arrow is pointing in the right direction on the display. I do the same as you - I set the mat cardinal points on the ground with a compass so that I can compare the aircraft on the mat with the orientation arrow on the compass rose on the screen. But you can orient the aircraft on the map in any direction and then perform that check - the aircraft doesn't need to be facing north to start up correctly. Does that answer your question, or did I misunderstand?

thank you for your reply yes it confirms what i believed,and as you say with the map i always unlock the compass icon on the map and it will turn it the same direction as the arrow on the orientation display it has been something that has stood me in good stead and is now a part of my normal startup routine

 

[Peio64270]

I quite understand your analogy, and I can only say that, if I had a totally automated catamaran (which would be my preference over a yacht), and I was trusting it to get me safely to a distant location, and it detected an anomaly and asked my to go pull a 360 out in the bay before heading out of sight of land...

...I'd be okay with the small inconvenience just for peace of mind.

Even though I was 99.99% sure it wasn't necessary.

Please read my answer to Meta4 which completes his analogy by the relation of a little personnal anecdote.
Maybe you'll realize that a new calibration in a perturbated environment can lead to catastrophic events when the perturbation diminishes, changes or disappears completely (my cans which are used one by one for cooking).
For example if you are with your drone close to a loudspeaker, it is very likely that the app will ask for a compass calibration. Do it for "peace of mind" and I guess that your peace will vanish very rapidly just after take off

 

[OldGuy]

So, what do say, @OldGuy

Are you willing to post your logs of the flight? I know I for one am curious.

I will post the flight record for the last and fatal flight of my MM on the 28th December as soon as I figure out how to do it. My young IT friend is not available to help me at the moment due to local holidays.

 

[Meta4]

I will post the flight record for the last and fatal flight of my MM on the 28th December as soon as I figure out how to do it.

Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report of the flight.
Come back and post a link to the report it gives you.

 

[Dan C]

The aircraft cannot "detect that north isn't where it should be" by comparing to GPS data, because GPS data have no direction information. As a result, your suggestion that this situation could trigger a recalibration request is wrong.

I put a question mark after that part. Meaning I’m not claiming anything, just spitballing.

But by all means, please tell us why DJI Go requests a compass calibration.

I just figured there had to be some logic behind it, but you guys insist there’s no reason for it. Apparently it’s totally random and DJI put that in there just to irritate us.

 

[Meta4]

I put a question mark after that part. Meaning I’m not claiming anything, just spitballing.

But by all means, please tell us why DJI Go requests a compass calibration.

I just figured there had to be some logic behind it, but you guys insist there’s no reason for it. Apparently it’s totally random and DJI put that in there just to irritate us.

I don't know why I'm doing this but ...
It's probably a mistake to assume that the app is (properly) requesting you to calibrate the compass.
DJI's message might be the problem.
If you aren't in a situation where the app is needlessly requesting calibration based on distance or time since last calibration, the compass has detected a reading out of the normal range.
Because of DJI's poor communications, they give you a screen message that doesn't explain that and just asks for a calibration.
You get the same message when the compass is disconnected and thus giving an out of normal range reading.
But as has been explained a few times already recalibrating the compass is not the solution to the problem.

If that answer isn't good enough for you
Tough.

 

[sar104]

I put a question mark after that part. Meaning I’m not claiming anything, just spitballing.

But by all means, please tell us why DJI Go requests a compass calibration.

I just figured there had to be some logic behind it, but you guys insist there’s no reason for it. Apparently it’s totally random and DJI put that in there just to irritate us.

I have no inside information on that question, but I can make some educated guesses. DJI is certainly aware that compass errors have resulted in many lost or damaged aircraft that resulted in warranty claims, and they have replaced numerous aircraft that crashed as a result of incorrectly initialized yaw errors. They have taken several steps to try to address that issue. The Mavic 2 includes the best effort on that front - it is capable of resetting the IMU yaw after takeoff, which is the most robust solution. Calibration requests are another approach, but interestingly out-of-calibration aircraft account for a very small fraction of these problems - I know that from the large number of logs that I've examined.

Having discussed this with DJI's engineering department, who understand the issue and implemented the Mavic 2 solution, my conclusion is that the calibration requests are a result of poor communication between engineering and support, since calibration basically is of very little use here. The time-based request could be argued as a periodic check that the aircraft hasn't changed its state of magnetization. The distance-based request is simply baffling, unless they think that transporting the aircraft carries an increased risk of changing its magnetic state.

 

[Dan C]

@Meta4 and @sar104 , thank you both for your responses.

First, let me remind everyone still reading this... My post that started this whole thing was stating why I think DJI's software asks for a calibration. That was my purpose. WHY do you get that message. Not if it was necessary... just why it happens. You two ridiculed my message as misinformed, then went on at length about what calibration does.

I thank you for your explanations. They have been informative. But allow me to remind you both of the core statement I was making on this whole matter of WHY a calibration is requested:

My experience has been that there is little rhyme or reason some of the time that I’m aware of, but that doesn’t mean there isn’t a reason.

Bottom line: I don’t lose any sleep over it. If it asks, I calibrate.

Now, I was rather thorough in my research before flying my drone. And page 55 of the Mavic Air user manual states:

Calibrating the Compass

It is recommended that the compass is calibrated in any of the following situations when flying outdoors:

1. Flying at a location farther than 31 miles (50 km) away from the last flight location.
2. The aircraft has not been flown for more than 30 days.
3. A compass interference warning appears in the DJI GO 4 app and/or the Aircraft Status Indicator blinks alternating red and yellow quickly.

Please note that I commented that I have found little rhyme or reason to much of this, merely that I find it expedient to calibrate when the software asks for it.

I also humbly included the fact that just because I don't know of w logical reason for the calibration request, doesn't mean there isn't a good reason for it.

And for this, you two have come after me in a rather uncalled-for fashion, and I am surprised moderation allowed it. It's okay, I don't really care, I'm merely surprised.

So the conversation continued, with you two, particularly Meta4, being very disparaging because apparently I'm too stupid to realize the conversation is about the uselessness of calibrating.

Odd, since as it was my post that triggered your ire, and my post was merely a casual observation about "why" the request might happen, but still it was deemed my failing that I couldn't see your points.

So this morning, I find Meta4 acknowledging:

...the compass has detected a reading out of the normal range.

Thank you. I was wondering about that and, though you haven't indicated "how" that might happen, at least it is an acknowledgement that it CAN happen.

And sar104 said:

...my conclusion is that the calibration requests are a result of poor communication between engineering and support, since calibration basically is of very little use here.

I find that very believable. I watched their videos about controlling the aircraft, and I can tell you what they say about "Follow Mode" is half wrong. The drone cannot reproduce what they show you in the video. Clearly, mistakes are made.

And yet, I'm still wondering how my "no rhyme or reason that I can see" comment rated a "you are wrong" response from you two.

Maybe it was because Meta4 perceived my message as a criticism of him, since I started with a crack about calibrating away from your cell phone, and sar104 is just sticking up for his buddy.

That would be odd, since my crack was at DJI, not Meta4, for suggesting you even can calibrate without your cell phone - at least, it is not possible as far as I can tell on my Mavic Air. No smart controller support, you see.


But even now, your position seems to be that calibration is a waste of time. Maybe so. The electromagnetic profile of the drone hasn't changed. You are sure of that.

You know, funny story. I remember years ago, when I was a kid, there was a radio tower not too far away, and sometimes we'd go over to about 1Km away from it with industrial fluorescent tubes in our hands, and watch them light up when we got close enough to the tower.

Induction is an amazing phenomenon.

We really shouldn't talk about the magnetic field of the drone, but rather the electromagnetic field, since the two are intimately intertwined. And I'm pretty sure that if you went within 1 Km of that old radio tower, it would induce a field within your drone.

Meta4, I reckon that would cause a, what did you call it... "a reading out of the normal range". Which would trigger a calibration request on the software, am I correct?

Yes yes, I know I know. Move away from the tower. Yeah, I got it the first time.

But I only ever argued about WHY you'd get the message. And this sounds like a perfect "why". And, it would obviously be an external, environmental reason.

Calibrating might not solve this anomaly, of course. You might have no choice but to move away from the tower.

But the tower would definitely be the "why", and I cannot see how I'm so wrong about that.

This would be an environmental trigger to an actual change in the drone's electromagnetic field as well.

I can't see how I'm so wrong about that, either.

Why you two have been so vehement about making this about something else, I really don't know.

I don't much care either.

Because if you forget the manual, and just look at what works, then here is what works for me and my Mavic Air.

If it asks for a calibration, I calibrate. It does not harm, and takes but a few seconds.

- If the calibration succeeds, I fly. I've never had any problems with location or RTH or anything else.
- If calibration fails, I move. I assume that whatever has caused the request is too strong right here, so I find a different spot, and try again. This has happened, and moving a little ways away has always fixed the problem.

Through this back and forth with you two, I have built a clearer picture in mind about what is going on. Thanks to sar104, I now know how calibration works, and what it does.

However, you guys have trashed my suggestions, yet I see now that they hold water.

Environment CAN trigger the request, and is in fact the most likely culprit.

DJI might have made a mistake, but then again, the manual seems to reflect a concern for changes in the environment, errors in the recorded data within the drone, and changes to the drones electromagnetic profile.

All of those things seem quite reasonable to me.

Lastly, returning to the OP's post (and my apologies for hijacking your thread, sir), I think that DJI might decline to accept responsibility for the loss of a drone where the pilot ignored a calibration request (is it even possible to launch under this condition?).

"Sir, we cannot be held responsible if you ignore the warnings of the software".

Somehow, I don't think quoting sar104 as a material expert is going to change that conversation.

For the record, you both seem to stand on the idea that recalibrating is never required. I think you are wrong. I am satisfied that there are real-world conditions that can indeed change the drone's electromagnetic profile, and it seems DJI are not 100% confident in their drones keeping that information intact over time.

I stand by my original statement. I can't always see why my drone asks me to calibrate the compass. I also don't much care. If it asks, I calibrate. I don't care how the drone does that, or what it does to achieve that, but it results in me being able to fly, and I figure it covers my butt with DJI should I ever have a need to claim from them.

If you two gentlemen still have an issue with that for some reason, have at it.

I'm done with this matter, and I am confident an unbiased reader would agree with my position which has always been simply why this request happens, my personal experience with it, and how I respond to it.

@sar104 I hope that should the day come that I need logs analyzed, that you'd be willing to help. You read those things like most of us read a newspaper. Very impressive.

But if you've taken this thread personally... so be it. Sorry you feel that way.

 

[sar104]

@Meta4 and @sar104 , thank you both for your responses.

First, let me remind everyone still reading this... My post that started this whole thing was stating why I think DJI's software asks for a calibration. That was my purpose. WHY do you get that message. Not if it was necessary... just why it happens. You two ridiculed my message as misinformed, then went on at length about what calibration does.

I thank you for your explanations. They have been informative. But allow me to remind you both of the core statement I was making on this whole matter of WHY a calibration is requested:



Now, I was rather thorough in my research before flying my drone. And page 55 of the Mavic Air user manual states:



Please note that I commented that I have found little rhyme or reason to much of this, merely that I find it expedient to calibrate when the software asks for it.

I also humbly included the fact that just because I don't know of w logical reason for the calibration request, doesn't mean there isn't a good reason for it.

And for this, you two have come after me in a rather uncalled-for fashion, and I am surprised moderation allowed it. It's okay, I don't really care, I'm merely surprised.

So the conversation continued, with you two, particularly Meta4, being very disparaging because apparently I'm too stupid to realize the conversation is about the uselessness of calibrating.

Odd, since as it was my post that triggered your ire, and my post was merely a casual observation about "why" the request might happen, but still it was deemed my failing that I couldn't see your points.

So this morning, I find Meta4 acknowledging:


Thank you. I was wondering about that and, though you haven't indicated "how" that might happen, at least it is an acknowledgement that it CAN happen.

And sar104 said:


I find that very believable. I watched their videos about controlling the aircraft, and I can tell you what they say about "Follow Mode" is half wrong. The drone cannot reproduce what they show you in the video. Clearly, mistakes are made.

And yet, I'm still wondering how my "no rhyme or reason that I can see" comment rated a "you are wrong" response from you two.

Maybe it was because Meta4 perceived my message as a criticism of him, since I started with a crack about calibrating away from your cell phone, and sar104 is just sticking up for his buddy.

That would be odd, since my crack was at DJI, not Meta4, for suggesting you even can calibrate without your cell phone - at least, it is not possible as far as I can tell on my Mavic Air. No smart controller support, you see.


But even now, your position seems to be that calibration is a waste of time. Maybe so. The electromagnetic profile of the drone hasn't changed. You are sure of that.

You know, funny story. I remember years ago, when I was a kid, there was a radio tower not too far away, and sometimes we'd go over to about 1Km away from it with industrial fluorescent tubes in our hands, and watch them light up when we got close enough to the tower.

Induction is an amazing phenomenon.

We really shouldn't talk about the magnetic field of the drone, but rather the electromagnetic field, since the two are intimately intertwined. And I'm pretty sure that if you went within 1 Km of that old radio tower, it would induce a field within your drone.

Meta4, I reckon that would cause a, what did you call it... "a reading out of the normal range". Which would trigger a calibration request on the software, am I correct?

Yes yes, I know I know. Move away from the tower. Yeah, I got it the first time.

But I only ever argued about WHY you'd get the message. And this sounds like a perfect "why". And, it would obviously be an external, environmental reason.

Calibrating might not solve this anomaly, of course. You might have no choice but to move away from the tower.

But the tower would definitely be the "why", and I cannot see how I'm so wrong about that.

This would be an environmental trigger to an actual change in the drone's electromagnetic field as well.

I can't see how I'm so wrong about that, either.

Why you two have been so vehement about making this about something else, I really don't know.

I don't much care either.

Because if you forget the manual, and just look at what works, then here is what works for me and my Mavic Air.

If it asks for a calibration, I calibrate. It does not harm, and takes but a few seconds.

- If the calibration succeeds, I fly. I've never had any problems with location or RTH or anything else.
- If calibration fails, I move. I assume that whatever has caused the request is too strong right here, so I find a different spot, and try again. This has happened, and moving a little ways away has always fixed the problem.

Through this back and forth with you two, I have built a clearer picture in mind about what is going on. Thanks to sar104, I now know how calibration world, and what it does.

However, you guys have trashed my suggestions, yet I see now that they hold water.

Environment CAN trigger the request, and is in fact the most likely culprit.

DJI might have made a mistake, but then again, the manual seems to reflect a concern for changes in the environment, errors in the recorded data within the drone, and changes to the drones electromagnetic profile.

All of those things seem quite reasonable to me.

Lastly, returning to the OP's post (and my apologies for hijacking your thread, sir), I think that DJI might decline to accept responsibility for the loss of a drone where the pilot ignored a calibration request (is it even possible to launch under this condition?).

"Sir, we cannot be held responsible if you ignore the warnings of the software".

Somehow, I don't think quoting sar104 as a material expert is going to change that conversation.

For the record, you both seem to stand on the idea that recalibrating is never required. I think you are wrong. I am satisfied that there are real-world conditions that can indeed change the drone's electromagnetic profile, and it seems DJI are not 100% confident in their drones keeping that information intact over time.

I stand by my original statement. I can't always see why my drone asks me to calibrate the compass. I also don't much care. If it asks, I calibrate. I don't care how the drone does that, or what it does to achieve that, but it results in me being able to fly, and I figure it covers my butt with DJI should I ever have a need to claim from them.

If you two gentlemen still have an issue with that for some reason, have at it.

I'm done with this matter, and I am confident an unbiased reader would agree with my position which has always been simply why this request happens, my personal experience with it, and how I respond to it.

@sar104 I hope that should the day come that I need logs analyzed, that you'd be willing to help. You read those things like most of us read a newspaper. Very impressive.

But if you've taken this thread personally... so be it. Sorry you feel that way.

Can you elaborate on what you mean by "electromagnetic field"? In physical terms, an electromagnetic field is quite different from a magnetic field - it's a traveling wave in the EM spectrum comprising orthogonal, in-phase, oscillating electric and magnetic fields. The drone doesn't have an electromagnetic field, and the compass doesn't detect EM waves - only static magnetic fields.

And to clarify regarding compass calibration requests - I'm not suggesting that you ignore them, and I usually (but not always) calibrate when requested. But if you look at the recorded calibration data and the resulting magnetic field strengths in the DAT files, then you will find that they do not change significantly as a result.

Nothing taken personally by me, so no need to worry on that account.

 

[Dan C]

Can you elaborate on what you mean by "electromagnetic field"? In physical terms, an electromagnetic field is quite different from a magnetic field - it's a traveling wave in the EM spectrum comprising orthogonal, in-phase, oscillating electric and magnetic fields. The drone doesn't have an electromagnetic field, and the compass doesn't detect EM waves - only static magnetic fields.

I'm not an engineer or physicist. That was a really long post I wrote, and perhaps I made a mistake on this part. Not core to my argument, but still...

My understanding suggests two things to me:

First, that a strong electromagnetic field could induce a current in the electronics of the drone. Induced current is why networking cables are twisted in pairs; the information is decoded by the difference between signals, not their amplitude. By twisting the cables, any current induced in one will be equally induced in the other, and the signal will transmit successfully.

I assumed that the drone could be susceptible to such interference and thus the data being processed could be corrupted.

Second, though a very weak influence, I understand that a strong electromagnetic field can in fact affect a magnetic field. It has to be pretty strong, which is probably why most of the time the issue is ferrous material.

Yet you've stated the compass doesn't detect these fields, and that is confusing. We are flirting with quantum theory now, and I'm certainly not particularly knowledgeable there.

But as a lay person, it seems to me that it is "common knowledge" that electronics can affect compasses. That might be wrong, but...

Here... a quick search:

The magneto-inductive technology is able to electronically sense the difference in the earth's magnetic field from a disturbance caused by external elements such as ferro-magnetic materials and the magnetic field generated by automobile electrical systems.

.....

Sources of magnetic fields in any automobile include permanent magnets mostly in its audio speakers, motors, electric currents flowing in its wiring-either dc or ac, and ferro-magnetic metals such as steel or iron.

(source)

Also, I recall that the calibration process for in-vehicle digital compasses includes turning on all "normally on" electronics -- lights, radios, etc. You can see why I'd be confused.

Perhaps this is not electromagnetic interference; I'd welcome your correction. But whatever the energy is, it does seem to be a problem, and it seemed reasonable to me as a trigger for the calibration messages.

And to clarify regarding compass calibration requests - I'm not suggesting that you ignore them, and I usually (but not always) calibrate when requested. But if you look at the recorded calibration data and the resulting magnetic field strengths in the DAT files, then you will find that they do not change significantly as a result.

Nothing taken personally by me, so no need to worry on that account.

Thank you. I appreciate that.

 

[Dan C]

FYI, for those interested in some of the deeper aspects of the subject of electromagnetic interference in navigating, you might find this article of interest:

Electromagnetic Interference Disrupts Bird Navigation, Hints at Quantum Action

It is not directly relevant to this thread because it is focused on biological "compasses", but it is fascinating when they get into the "how" the interference occurs, and how weak the signals can be.

 

[Olav van Gerven]

The first step to improbement is admitting there is a problem. Though there is an advantage of being foolish while at age: Being foolish when you're young, people will scold you and say "grow up!" while being at age an foolish people will look with an understanding view "oh, no problem, let him be foolish, he is old..."

 

[OldGuy]

The first step to improbement is admitting there is a problem. Though there is an advantage of being foolish while at age: Being foolish when you're young, people will scold you and say "grow up!" while being at age an foolish people will look with an understanding view "oh, no problem, let him be foolish, he is old..."

Thanks for the encouragement Olav.

 

[OldGuy]

Go to DJI Flight Log Viewer | Phantom Help
Follow the instructions there to upload your flight record from your phone or tablet.
That will give you a detailed report of the flight.
Come back and post a link to the report it gives you.

I have found this. Is this what we are looking for?