Got this GPS message today

[Howcroft22]

So today I was coming in when I got the low battery warning. And I was not far away. The drone was right in front of me and there were obviously plenty of satellites in range. And I had been flying back-and-forth in this area with no issues before. And all of a sudden I got this message saying the GPS signal was gone. Luckily the drone was right next to me otherwise I would have been terrified. Any ideas why this would happen when it clearly shows I have lots of satellites. Some reason it went in atti mode. But why when there were 18 satellites? Also I should mention that the signal came back a minute or so later and went back to GPS mode.

 

[Anthony]

We're you in sports mode ??

 

[Howcroft22]

We're you in sports mode ??

Yes

 

[Anthony]

Yes

How old is your mavic ?

I had to have mine replaced as everytime I put it into sports mode and flew full speed I got the message that you have displayed.

 

[dwallersv]

View attachment 28295Any ideas why this would happen when it clearly shows I have lots of satellites. Some reason it went in atti mode. But why when there were 18 satellites? Also I should mention that the signal came back a minute or so later and went back to GPS mode.

You have misinterpreted the error message on the screen. You compass has completely failed, not GPS.

The compass is a different piece of hardware. Without a functioning compass, the aircraft can not tell what direction it's pointing. This can be inferred while moving, but it is far too imprecise for flight control. The sensitivity (both angular and sample rate) of the digital compass is necessary for flight control.

As a consequence, the aircraft switched to ATTI mode because all the flight controller can do is maintain attitude via the ICU. Even though it knows location via GPS, it can not hold position because it doesn't know it's heading.

Since the aircraft was close to you (and the ground, and surrounding ground environment) it probably was affected by some external magnetic field. A good candidate would be an electrical transformer, telephone patch box, etc. However, at this point it's near impossible to find out what unless it can be repeated.

 

[Howcroft22]

How old is your mavic ?

I had to have mine replaced as everytime I put it into sports mode and flew full speed I got the message that you have displayed.

A week old.

 

[Howcroft22]

You have misinterpreted the error message on the screen. You compass has completely failed, not GPS.

The compass is a different piece of hardware. Without a functioning compass, the aircraft can not tell what direction it's pointing. This can be inferred while moving, but it is far too imprecise for flight control. The sensitivity (both angular and sample rate) of the digital compass is necessary for flight control.

As a consequence, the aircraft switched to ATTI mode because all the flight controller can do is maintain attitude via the ICU. Even though it knows location via GPS, it can not hold position because it doesn't know it's heading.

I saw that as well. Why would the compass do this?

 

[Anthony]

A week old.

OK I would check the compass readings and if you have updated the Firmware refresh it as DJI support will only ask you to do this anyway.

 

[dwallersv]

I wouldn't worry about it unless it happens again. Take it out to somewhere open and safe to fly, like a big field or parking lot. Do some test flying, keeping it close and relatively low, progressively go further and higher and come back, do some close flying in Sport mode too.

If the error doesn't reoccur and everything works well, you can chalk it up to some anomalous magnetic field of big hunk of metal nearby, and carry on a happy pilot.

Don't calibrate the compass unless GO4 tells you to.

 

[james_mav]

I saw that as well. Why would the compass do this?

It looks pretty cold there. I wouldn't rule out temp as a factor. Just think how cold the Mavic is flying at 30 mph.

 

[Howcroft22]

It looks pretty cold there. I wouldn't rule out temp as a factor. Just think how cold the Mavic is flying at 30 mph.

Ok thanks

 

[Howcroft22]

I wouldn't worry about it unless it happens again. Take it out to somewhere open and safe to fly, like a big field or parking lot. Do some test flying, keeping it close and relatively low, progressively go further and higher and come back, do some close flying in Sport mode too.

If the error doesn't reoccur and everything works well, you can chalk it up to some anomalous magnetic field of big hunk of metal nearby, and carry on a happy pilot.

Don't calibrate the compass unless GO4 tells you to.

I think when I did calibrate it. The vehicle was like 30 feet away. Maybe it was not an open enough area?

 

[ibuyufo]

Don't calibrate the compass if it doesn't ask you to do it, even if you're 200 miles away from where you originally calibrated it. I know DJI recommends calibration every single time you fly but you're increasing your chances of a bad compass calibration.

 

[SwatKat]

Don't calibrate the compass if it doesn't ask you to do it, even if you're 200 miles away from where you originally calibrated it. I know DJI recommends calibration every single time you fly but you're increasing your chances of a bad compass calibration.

That makes no sense whatsoever (at least to me) . It is akin to saying I am depending on my car's intelligence to tell me when to go perform oil changes and preventive maintenance. Much like, if my car does not tell me it is time for an oil change, I am going to go against common sense and not do it, even if I have been driving for ever and am past the normal mile range for maintenance.

Experts, can you please elaborate on this? True/false, good practices/BS? I personally feel I would do those things even if not required just to make sure I do everything in my control not to crash my drone.

@sar104 @msinger

 

[ibuyufo]

Calibrate the mavic compass at each start?

 

[ibuyufo]

I've flown the phantom 4 without calibration from the factory as well as the mavic pro and no issue.

 

[SwatKat]

I appreciate the link to the prompt, but most of the answers there are speculative/experiential (had already seen that discussion). I am wondering about this from two angles:

1. Why would the manufacturer recommend it?
2. Even so, how (and by how, I mean a scientific explanation) would it hurt to align your device's compass, or let me say, re-align it every time you fly? As long as you make sure that you are not calibrating it around metal or any of the caveats as we know, how is it detrimental? It is only being cautious, in my opinion.

I am just curious about this from an electronics/systems point of view, more like gathering in-depth knowledge.

 

[ibuyufo]

1. I don't know why DJI would recommend recalibrating the compass every time when there is no indication that it needs to be calibrated. The mavic/phantom would know if there was some type of magnetic interference as it can detect it and it can also detect if the compass needs calibration.

2. Maybe this ties into your first question as the earth has variations in the magnetic field that calibration would compensate for this background variation and magnetic field's inclination. These variations are very minuscule that it's maybe being over blown by DJI and recommending to recalibrate each flight.

 

[locoman]

My Mavic, asks me to calibrate the compass at startup about 90% of the time. No big deal, to me it is just part of the preflight process.

 

[ibuyufo]

My Mavic, asks me to calibrate the compass at startup about 90% of the time. No big deal, to me it is just part of the preflight process.

That can't be right. My mavic and phantom 4 never ask to re-calibrate the compass.