The compass, what Mavic uses it for?

[Will.i.am]

Very briefly, heading is which way the craft is pointing, track is where you have been, and course is where you want to go. The compass (actually the Mavic has 2) provides heading, GPS provides track, and your stick inputs provide course. There are also accelerometers or gyros, which tell whether the craft is level or not. When you provide stick input, the IMU needs the heading to be able to command the right motors to spin to fly the course. You don't need GPS to fly (ie ATTI mode), but you do need it to maintain position (hover) and to fly to a set of coordinates (RTH).

 

[SRJ_Mavic_PRO]

Yeah I wasn't so lucky the next time it happened. Hence it is with DJI.

That is freakin scary!! I hate to see that happen if there were people around watching!

 

[Robbyg]

By this I take it you mean literal fly aways into the yonder never to return, as compare to spontaneously flying away laterally for no apparent reason, like this. I have DJI looking at the log of this. So they will soon tell me if is Pilots error.

To view this content we will need your consent to set third party cookies.
For more detailed information, see our cookies page.

Accept third party cookies

This is a RTH precision Landing. Arrives back over home point, aligns heading, descends, precision lands bombsiting the target - then rapidly spears off 40' in the last few feet of the descent when it all looked home and hosed. Logs cleary show I was hands off through out, with my first input being to toggle the mode switch to prevent a crash 30' away. I am puzzled as to why DJI are allowing autoland to continue with horizontal speeds like this.

Can you upload the log from the Mavics black box?
We can probably tell you exactly what happened.

Rob

 

[Wombat55]

The compass is a convenience in that it immediately gives information on the directional orientation of the drone. But it's also true that the drone should be able to determine its directional orientation by flying forward a short distance and looking at the change in its GPS coordinates. Similarly, the Mavic should be able to execute an RTH command even if its compass failed by using GPS alone. Don't know if it actually can but in principle it should be able to.

It would be surprising to find that a Mavic can't fly at or near the magnetic north or south poles because its crippled without compass information even if it has a perfectly good GPS lock.

 

[Logger]

Can you upload the log from the Mavics black box?
We can probably tell you exactly what happened.
Rob

Rob, Have already had our local expert look at it. I had thought perhaps I might have been landing on buried steel water wipe and therfore asked him to review it. The report back was No Geomagnetic interference and no mention of any obvious cause.

Here is the csv from the aircraft DAT. 92 sec mark is where it happened.
FLY065.csv

MagY spiked a bit, but I think that was an effect rather than a cause.

Variations of this lateral fly off happened to me three times in the past few weeks with the same refurb Mavic at different locations. Always with autoland or precision landing. Never saw it happen with my original unit in over 350 flights..

 

[Will.i.am]

The compass is a convenience in that it immediately gives information on the directional orientation of the drone. But it's also true that the drone should be able to determine its directional orientation by flying forward a short distance and looking at the change in its GPS coordinates. Similarly, the Mavic should be able to execute an RTH command even if its compass failed by using GPS alone. Don't know if it actually can but in principle it should be able to.

It would be surprising to find that a Mavic can't fly at or near the magnetic north or south poles because its crippled without compass information even if it has a perfectly good GPS lock.

The compass is not "a convenience". It is absolutely essential to the safe flight of the Mavic, or any aircraft,. That's why there are two of them, and not two GPS systems. Even more critical to a quadcopter, which can fly in any directional orientation. Without a compass, and knowing which way the front of the Mavic is pointing, the IMU does not know which motors to activate to fly where you want it to. "Flying forward" has no meaning to a GPS, which just provides position. The difference between two positions can be used to compute a track, not a heading.

Here is some useful reading, if you're interested. Course (navigation) - Wikipedia. All pilots, even MavicPilots should know these basics.

In the old days before GPS, pilots could navigate an aircraft with just a compass and nothing else.

 

[ed1nh0]

This is a RTH precision Landing.

Gzuz! That was close.
Almost a "precision fail"!

 

[BerndM]

Thats a good question, don't think i've seen any flyway threads. The "fly away with the tail wind" kind of threads do not count.

There a quite a few of these in the Mavic Pro Help section

 

[Wombat55]

The compass is not "a convenience". It is absolutely essential to the safe flight of the Mavic, or any aircraft,. That's why there are two of them, and not two GPS systems. Even more critical to a quadcopter, which can fly in any directional orientation. Without a compass, and knowing which way the front of the Mavic is pointing, the IMU does not know which motors to activate to fly where you want it to. "Flying forward" has no meaning to a GPS, which just provides position. The difference between two positions can be used to compute a track, not a heading.

Here is some useful reading, if you're interested. Course (navigation) - Wikipedia. All pilots, even MavicPilots should know these basics.

In the old days before GPS, pilots could navigate an aircraft with just a compass and nothing else.

No, I'm sorry but you're wrong about it being "absolutely essential" in the case of drones. A compass failure on a drone would be an inconvenience but would not lead to any lost capabilities if GPS is still operational. Even without a working compass a drone can determine which way it is pointing by flying forward a few yards and noting in which direction it has moved according to its GPS readings. That gives the drone its orientation. No compass required. Admittedly, it's not as quick or perhaps as accurate as an instant reading from a working compass, but it is a perfectly viable fallback option in case of a compass failure.

Finally, even a working compass is of little use in determining aircraft orientation if one is at or near the magnetic North or South Pole. The GPS procedure I just described, however, would work even near the magnetic poles. So, no, a well designed drone should not have to go haywire in its navigational capabilities even if it is flying near one of the magnetic poles.

 

[flyNfrank]

Very briefly, heading is which way the craft is pointing, track is where you have been, and course is where you want to go. The compass (actually the Mavic has 2) provides heading, GPS provides track, and your stick inputs provide course. There are also accelerometers or gyros, which tell whether the craft is level or not. When you provide stick input, the IMU needs the heading to be able to command the right motors to spin to fly the course. You don't need GPS to fly (ie ATTI mode), but you do need it to maintain position (hover) and to fly to a set of coordinates (RTH).

I'm not positive, I think there is 3 compasses associated with the Mavic.

 

[Logger]

...working compass is of little use in determining aircraft orientation if one is at or near the magnetic North or South Pole. The GPS procedure I just described, however, would work even near the magnetic poles....

It might with some other drone but not the Mavic. P-mode (aka the GPS mode of which you speak) is not available for use in Polar areas. Whilst we know a regular GPS will work there, the mag compass will not. This would suggest the compass is essential for P-Mode. p50 of the manual btw.

 

[Robbyg]

Rob, Have already had our local expert look at it. I had thought perhaps I might have been landing on buried steel water wipe and therfore asked him to review it. The report back was No Geomagnetic interference and no mention of any obvious cause.

Here is the csv from the aircraft DAT. 92 sec mark is where it happened.
FLY065.csv

MagY spiked a bit, but I think that was an effect rather than a cause.

Variations of this lateral fly off happened to me three times in the past few weeks with the same refurb Mavic at different locations. Always with autoland or precision landing. Never saw it happen with my original unit in over 350 flights..

Yeah I see Logger. It's another defective Mavic case.
The world may never know what happened. I suspect DJI will give you some sort of generic answer and just replace it.

Rob

 

[Logger]

Yeah I see Logger. It's another defective Mavic case.
The world may never know what happened. I suspect DJI will give you some sort of generic answer and just replace it.

Rob

I take it nothing in the logs jumped out at you either?
Will wait and see what DJI come back with. Warranty replacement would be nice so fingers crossed.

 

[AnzacJack]

No, I'm sorry but you're wrong about it being "absolutely essential" in the case of drones. A compass failure on a drone would be an inconvenience but would not lead to any lost capabilities if GPS is still operational. Even without a working compass a drone can determine which way it is pointing by flying forward a few yards and noting in which direction it has moved according to its GPS readings. That gives the drone its orientation. No compass required. Admittedly, it's not as quick or perhaps as accurate as an instant reading from a working compass, but it is a perfectly viable fallback option in case of a compass failure.

Finally, even a working compass is of little use in determining aircraft orientation if one is at or near the magnetic North or South Pole. The GPS procedure I just described, however, would work even near the magnetic poles. So, no, a well designed drone should not have to go haywire in its navigational capabilities even if it is flying near one of the magnetic poles.

And yet this hasnt been implemented....
Why do you think this is?

 

[Wombat55]

And yet this hasnt been implemented....
Why do you think this is?

Probably because the compasses are reliable enough and there aren't massive numbers of people flying their Mavics at the North and South magnetic poles, and so for DJI to implement the fallback option I described is too low on their list of priorities.

 

[AnzacJack]

So it must be more efficient. And that is the answer for the compass use

 

[Dragonfly]

The compass is not "a convenience". It is absolutely essential to the safe flight of the Mavic, or any aircraft,. That's why there are two of them, and not two GPS systems. Even more critical to a quadcopter, which can fly in any directional orientation. Without a compass, and knowing which way the front of the Mavic is pointing, the IMU does not know which motors to activate to fly where you want it to. "Flying forward" has no meaning to a GPS, which just provides position. The difference between two positions can be used to compute a track, not a heading.

Here is some useful reading, if you're interested. Course (navigation) - Wikipedia. All pilots, even MavicPilots should know these basics.

In the old days before GPS, pilots could navigate an aircraft with just a compass and nothing else.

Thats the point I tried to gey across to him by standing in a room and walking to a corner backwards but he doesnt get it. Once the drone is moving the GPS will provide a compass bearing its travling on but the GPS still doesnt know which is the front or side or back end of the craft. His analysis of his GPS in his car is irrelivent as it does not need to rotate or move, it is stationary in its bracket and only needs to provide a bearing from GPS data once the vehiche starts moving. The drone needs a compass to turn its front in the right direction yoh comand via the RC to travel in that direction send it.

 

[Dragonfly]

No, I'm sorry but you're wrong about it being "absolutely essential" in the case of drones. A compass failure on a drone would be an inconvenience but would not lead to any lost capabilities if GPS is still operational. Even without a working compass a drone can determine which way it is pointing by flying forward a few yards and noting in which direction it has moved according to its GPS readings. That gives the drone its orientation. No compass required. Admittedly, it's not as quick or perhaps as accurate as an instant reading from a working compass, but it is a perfectly viable fallback option in case of a compass failure.

Finally, even a working compass is of little use in determining aircraft orientation if one is at or near the magnetic North or South Pole. The GPS procedure I just described, however, would work even near the magnetic poles. So, no, a well designed drone should not have to go haywire in its navigational capabilities even if it is flying near one of the magnetic poles.

Sorry to inform you, but takaway the compass and your drone wont fly. You can do without GPS but not compass.

 

[Dragonfly]

I'm not positive, I think there is 3 compasses associated with the Mavic.

Two

 

[Shayneb123]

Your run of the mill mobile phone does those calculation, they aren't as complex as you describe, really. Its actually as simple as knowing your position now, knowing your position 1 second later, and doing a simle math. Or, indeed, using longer history and filtering it to some extent. I am not saying having a compass is a bad thing!!! What i am saying is that i don't understand why not having it is considered potentially deadly for the bird!

Phones don't have a compass per say but they do have a magnetometer which is basically the same thing and this tells them their heading. This is how sky maps work