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Compas errorr and ATTI and no visual sight is this salveable?
1642 23 2018-7-11
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andy10
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There are situations where the AC is more or less lost. All we hope that such might not happen to you. But what if do?
For instance:  You have no visual contact and get compass error. The first thing you will probably do is switch to ATTI. But the problem is if you can't see the drone.
I think that the heading information at left down corner is of no use. Can you still do something or just say by by birdie?
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Labroides
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What to do? if  For instance: You have no visual contact and get compass error.
You're hypothetical situation is something that shouldn't ever happen to you.
Compass errors aren't things that just happen and they aren't faults of the compass.
As long as you don't go launching from steel or reinforced concrete surfaces you should never see a compass warning.
The first thing you will probably do is switch to ATTI.
If you do mess up your compass by launching from a magnetically dirty area, the Phantom will drop into atti mode before you could switch it anyway.
Flicking the flight mode switch wouldn't make any difference.

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Nigel_
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I've never tested it, but I would expect that you can fly back using the map.  The GPS should still be providing location information, even though it isn't being used for flight control, so the map location should be correct.  The orientation may be wrong so you may need to fly at some speed and watch the direction it heads on the map, then turn the appropriate amount.
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andy10
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So if you not experience the compass error at take off than this will not happen during the flight. Problems with flying around the magnetic objects are therefore not the compass error but false magnetic pole? Is any warning message for that?
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Nigel_
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andy10 Posted at 2018-7-12 00:58
So if you not experience the compass error at take off than this will not happen during the flight. Problems with flying around the magnetic objects are therefore not the compass error but false magnetic pole? Is any warning message for that?

If you take off near a small magnet, like a sunroof electric motor, then the compass will tare|zero|calibrate itself to the magnetic field at takeoff and you will have a compass problem when you leave the small magnetic field at maybe 2 meters distance.

If you take off near a big magnet, like a steel chain-link fence, then the compass will tare itself to the magnetic field at takeoff and you will have a compass problem when you leave the big magnetic field at maybe 15 meters distance.

If you take off with no magnets near then the compass will tare itself to the earths magnetic field at takeoff and you will have no compass problems unless you fly near a large magnet, like an old steel bridge or an iron ore quarry.  When you enter the large magnetic filed at maybe at 30 meters distance the aircraft will start to fly in curves and if the  magnetic field gets stronger you will get compass warnings and maybe an automatic switch to atti mode.

In all cases the warnings/errors are the same because the aircraft can not tell the difference.


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Mark The Droner
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Nigel_ Posted at 2018-7-12 02:07
If you take off near a small magnet, like a sunroof electric motor, then the compass will tare|zero|calibrate itself to the magnetic field at takeoff and you will have a compass problem when you leave the small magnetic field at maybe 2 meters distance.

If you take off near a big magnet, like a steel chain-link fence, then the compass will tare itself to the magnetic field at takeoff and you will have a compass problem when you leave the big magnetic field at maybe 15 meters distance.

Here's my understanding and please tell me if you think I'm wrong:

If your compass is already properly calibrated and you take off from a field with no metal around, everything will likely be fine.

If your compass is already properly calibrated and you take off from a steel bridge or something, you may get compass errors, but once you launch and get away from the bridge, the compass will behave correctly and the compass errors will cease.  This is, of course, with the assumption that the magnetic field of the bridge wasn't so strong so as to damage the compass calibration.

OTOH, if you are at a steel bridge or something and calibrate the compass at the bridge, you're basically doomed.  

Agree?
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solentlife
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Mark The Droner Posted at 2018-7-12 03:07
Here's my understanding and please tell me if you think I'm wrong:

If your compass is already properly calibrated and you take off from a field with no metal around, everything will likely be fine.

Depends who is answering !!

Basically the AC will detect an anomaly and react with warning. Whether its at Home Point on the Bridge or you fly to the bridge and it then detects ...

Read about the guy with the flight near to a Silo ....

I'll not describe Variation, Deviation and all the factors in compasses and the Geomagnetic planes / contours as that only brings out the 'others' with their theories.

Suffice to say that the AC has a basic variation programmed in, it calibrates to allow for its own form as well. External influences that are outside of those cause the warnings when you power up and it detects variance. Its a few steps up from the basic electronic digital compass - of which I have many types and forms.

Back to OP question ? I would suggest that flying according to the screen video and map could be possible ... initially you would have to work out direction as the compass can no longer provide that .. the GPS can calculate required direction / distance - but it now has no reference to give Flight Controller to orientate for direction. So pray you have good video screen !! And that you know the layout.
Not every FPV machine has Compass ... my 450 FPV Quad has no compass but full GPS / On screen data etc. It has no P-GPS mode - it is totally ATTI - pilot fly machine.  I could take that well out of VLOS and fly back ... if I wanted to.

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Nigel_
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Mark The Droner Posted at 2018-7-12 03:07
Here's my understanding and please tell me if you think I'm wrong:

If your compass is already properly calibrated and you take off from a field with no metal around, everything will likely be fine.

That is not quite right because the compass has two calibrations, the one you do manually which corrects for the magnetic field of the aircraft and an automatic one done before take off which corrects for the magnetic field of the local area.  The 2nd one is the reason you can take the Phantom 4 around the Earth and not need to recalibrate the compass every time you move, it also means that if you take off from a steel bridge then you need to stay within the magnetic field of the bridge to avoid disaster.  Note that iron bridges and modern welded steel bridges tend to be OK because they don't have much magnetic field.
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Labroides
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Mark The Droner Posted at 2018-7-12 03:07
Here's my understanding and please tell me if you think I'm wrong:

If your compass is already properly calibrated and you take off from a field with no metal around, everything will likely be fine.

If your compass is already properly calibrated and you take off from a field with no metal around, everything will likely be fine.
Yes

If your compass is already properly calibrated and you take off from a steel bridge or something, you may get compass errors, but once you launch and get away from the bridge, the compass will behave correctly and the compass errors will cease.  This is, of course, with the assumption that the magnetic field of the bridge wasn't so strong so as to damage the compass calibration.
No.
Post #5 tells it fairly well.
Launch from a steel or reinforced concrete surface and you risk serious issues and maybe crashing or losing the Phantom.
The problem will become apparent when you get away from the launch point and It doesn't automatically fix it self when you get further away.
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solentlife
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Its actually easily observable ...

I assumed that like most digital and normal compasses - if the source of anomaly is removed - the compass would automatically 'fall' back to correct .. unless field was so strong that the unit A B C components have been affected. Observation I have seen of my own and others P3's show this is not always true with our compasses.

Pick a bad spot to power up and you get Compass Error. Now pick up the AC and move WITHOUT powering off ... the error warning can often remain on screen.

Now repeat that but this time power down and then move to same second spot - power up again and error is not there. This i have seen so often that now I don't even think about it ... if I get error ... I power down and move before powering up again. Usually does the trick.

Lets extrapolate ... we often assume that taking off from a bad location will correct as you lose influence of that location  - well I think a few posts of people having lost P3 / P4's from boat jetties, concrete slabs ... patios etc. says enough !

OK this matter of earths variation and auto calibrating. Yes that's fine - BUT earth is not uniform or even in its magnetic distribution ... a quick look at a variation Chart will soon show that. The flux lines are irregularly shaped and also actually are slowly moving. The chart also indicates pockets of abnormal variation due to earths structure ... iron ore deposits, etc.
The programmed factors only act for averaged variation - the calibration then per location sorts the final. But for practical purposes you can usually forget doing it again when moved ...

Something that also affects compass correction - is the orientation of the compass and its surrounding unit structure to the lines of flux passing through it. The compass has deviation due to orientation and this is a part of the compass dance reason ...
Ever calibrated a compass on a boat or in a car ? Done the 360 and adjustments ? same ...

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solentlife
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"Note that iron bridges and modern welded steel bridges tend to be OK because they don't have much magnetic field."

Nice one ... except ....

The bridge is not acting as a magnet ... not like the U bar you buy or the Neodynium in your Brushless motor. The Bridge is subject to magnetic flux passing through it and around it and causes modification of magnetic effects in its surroundings.

The compass whether mechanical or digital is attracted to the IRON ... it does not have to be itself a magnet. Test with a steel object ... nothing happens ... then pass a hand held compass over the structure - the magnetic pointer tries to snap to the IRON structure.

Correctors for Standard Compasses are Soft Iron Sphere's (Kelvin's Balls) ... they are non magnetic themselves but attract magnets just the same. Moving them toward or away from the needle is based on the magnetic flux pattern passing through them and its subsequent modification.

Blimey this is all taking me back to Marine College and the years of Navigation Classes I had ... as you get deeper into it - it can get extremely deep mind boggling stuff !

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Nigel_
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solentlife Posted at 2018-7-12 07:56
Its actually easily observable ...

I assumed that like most digital and normal compasses - if the source of anomaly is removed - the compass would automatically 'fall' back to correct .. unless field was so strong that the unit A B C components have been affected. Observation I have seen of my own and others P3's show this is not always true with our compasses.

"The programmed factors only act for averaged variation"
I don't think it has any programmed factors for location on Earth, I think it just zeros itself to the current measurement shortly after power-on, which suggests it must be able to sense gravity to know if it is not standing on flat ground.

What puzzles me is why it can't have a fall-back to the gravity sensor if the compass fails, it might not fly as smoothly but other drones show that you can fly OK without a compass and only OK flight would be better than falling into Atti and getting lost.
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hallmark007
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Labroids is correct, I’ll try explain what happens below.

The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will both move together 90 degrees and no problems.
If you put your Aircraft on the ground and there is magnetic interference only the heading of your compass will change, your aircraft will still take off. But when it clears magnetic interference compass will then move to correct heading which you would think was great. But No, what happens is IMU is then conflicted and confused because of this sudden movement by compass, so you receive IMU exceptional heading warning, your aircraft cannot deal with data conflict so decides to switch to Atti mode dropping gps in favour of compass simply because aircraft can fly without gps but not compass.
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solentlife
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Nigel_ Posted at 2018-7-12 08:15
"The programmed factors only act for averaged variation"
I don't think it has any programmed factors for location on Earth, I think it just zeros itself to the current measurement shortly after power-on, which suggests it must be able to sense gravity to know if it is not standing on flat ground.

Its actually not hard to have an algorythm in there for it .. but it will not be truly accurate because of the non-uniform geomagnetic lines.
It is possible it zeroes itself without such programming - to do that it must only accept a range and anything out side of it is error. Puts in question areas with high variation .... so I'm back to programmed averaging.

When the power is off ... there is nothing telling the AC its orientation, attitude or position. Fire it up and two things happen once Flight Controller / boards have initialised ready to accept data ... Compass settles, GPS accepts sats. The GPS has no idea of orientation ... all it knows at any time is position at that moment in time. Speed / movement / direction is all based on repeated GPS positions comparison by EXTERNAL software ... NOT the GPS.
To get movement to do RTH or Waypoint to Waypoint - Compass MUST set the reference so course based on GPS position comparison can be made.

Gravity sensor ? Sorry - how can that be any use ? I use many models without Compass and none have Gravity Sensors ... what they have are ACCELEROMETERS ... which detect acceleration in a plane of movement. But means nothing if it cannot be referenced. All it can do is smooth a hover or path YOU tell it fly ...

GPS on a Phantom is virtually useless without Compass for the auto flight software ... but is still useful to us when WE fly the model as in ATTI but still receiving sat data, but no compass.

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solentlife
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hallmark007 Posted at 2018-7-12 08:52
Labroids is correct, I’ll try explain what happens below.

The best way I can explain this is. If you put your Aircraft on the ground in normal circumstances, start it up, then lift it up and turn it 90 degrees to the right both your compass heading and IMU will both move together 90 degrees and no problems.

Who says you cannot fly without Compass ? Of course you can ... its just that you have no reference for smart autonomous flight ...

There are hundreds of other brand Quads / Tri's / Multis and Helicopters / fixed wing flying without Compass ... my 450 FPV Quad has no compass but has GPS. It means I manually fly it all time.

Nigel
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hallmark007
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solentlife Posted at 2018-7-12 10:17
Who says you cannot fly without Compass ? Of course you can ... its just that you have no reference for smart autonomous flight ...

There are hundreds of other brand Quads / Tri's / Multis and Helicopters / fixed wing flying without Compass ... my 450 FPV Quad has no compass but has GPS. It means I manually fly it all time.

I’m talking about P4Pro , maybe you have experience with flying it without compass you can let us know what to do,
I was just explaining what happens with these aircraft, I took it this is what op was looking for.
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Labroides
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solentlife Posted at 2018-7-12 03:21
Depends who is answering !!

Basically the AC will detect an anomaly and react with warning. Whether its at Home Point on the Bridge or you fly to the bridge and it then detects ...

Suffice to say that the AC has a basic variation programmed in, it calibrates to allow for its own form as well.
Do you have anything to support this?
It appears that the compass has no such programming, which would only be needed for converting magnetic north to true north.
But there's no need for that with a Phantom.
All it needs is a constant indication of direction - and in the case of the Phantom, that's a constant indication of magnetic north.
Magnetic variation doesn't matter to the Phantom.

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Eric13
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Labroides Posted at 2018-7-12 04:40
If your compass is already properly calibrated and you take off from a field with no metal around, everything will likely be fine.
Yes

"...once you launch and get away from the bridge, the compass will behave correctly and the compass errors will cease.  This is, of course, with the assumption that the magnetic field of the bridge wasn't so strong so as to damage the compass calibration.
No.
Post #5 tells it fairly well."

It's different for me.
Yes - my P3S was never able to 'recover' once it went into Atti mode due to compass issues.
My P4P always recovers, I had that 3-4 times so far. It'll pop back into P-GPS mode after a while, it may take up to 30 sec or so.

Post # 5 makes no sense at all!
First of all you can't take off so close to a fence that the metal would interfere - because the props would hit the fence.
And flying close to metal objects in order for them to interfere with the compass - that would need to be within a range below 3 feet.

I often fly very close to metal structures and never had an issue.
And I can take off from metal or concret without issues if I raise the drone by my little camping table less than 1m high.
My personal guess is that beyond 0.5 meters the drone's compass won't get disturbed my metal.


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solentlife
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Labroides Posted at 2018-7-12 14:20
Suffice to say that the AC has a basic variation programmed in, it calibrates to allow for its own form as well.
Do you have anything to support this?
It appears that the compass has no such programming, which would only be needed for converting magnetic north to true north.

I have not said conversion to True from Magnetic ... that's a totally different ball game and I agree with you is unnecessary.

What we do have though is a Flight Controller and Digital Compass that interact to give a directional reference. Then GPS position data repeated can then be used to 'fly home' autonomously.

Problem is that AC can detect abnormal magnetic effects before and during flight. If it was just looking for APARENT Magnetic North ... actually its termed COMPASS NORTH as its always with error of Deviation and Variation ... then why would an error get thrown up  when magnetic influence occurs ?

Its my question and always has been - if the machine is powered up and then gives an Error ... where does it get the information from to decide its an error ? It must have a programmed reference. Whether that's from previous calibration or actual programmed in data ... it has to have something to compare.

Another suggested that GPS / Flight Controller would get into conflict if Compass suddenly changed due to outside influence .......... how ? GPS and Flight Controller have no way to detect which way AC is pointing themselves.  So how does FC now know that Compass has shifted in error ?

I'm enjoying this debate ... its giving me a welcome break from the daily drudge of supplying oil / fuel to ...... well we'll leave that bit out !!

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solentlife
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hallmark007 Posted at 2018-7-12 10:26
I’m talking about P4Pro , maybe you have experience with flying it without compass you can let us know what to do,
I was just explaining what happens with these aircraft, I took it this is what op was looking for.

The OP has a range of AC ... Mavic .. P4 and P3's ... so who knows which one he's talking about.

I assume he's talking generally hoping it applies to all. And that is where my post comes from.

Let me ask you a question .... Can you fly your P4P when it drops to ATTI because Compass has error ? Now in light of OP question - it appears he's asking if you can get it to fly home ... can you salvage the situation ... not can you take-off.

So - can you fly your P4P if it gives Compass error during flight ? Can you manually fly it home ? I hope so - because if you cannot ... then somethings seriously wrong.

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Eric13
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solentlife Posted at 2018-7-13 01:40
The OP has a range of AC ... Mavic .. P4 and P3's ... so who knows which one he's talking about.

I assume he's talking generally hoping it applies to all. And that is where my post comes from.

"So - can you fly your P4P if it gives Compass error during flight ? Can you manually fly it home ?"

Yes - that's possible. It's just like any other Atti flight. But it's not necessary to bring it home.
I just fly the drone to some safe space where I can control it easily and wait for P-GPS to kick back in.

See video below as sample. I took off from stairs going over a dyke since it was very windy on top.
I forgot they were made of concrete ;-)

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solentlife
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Hi Eric13 .... I agree and I have done similar ... I have a pontoon for my yachts at bottom of garden as well as concrete base slabs the Guest Mobile stands on ... taking off from those can be a gamble.

I don't use them now as illustrated earlier ... I have had AC not lose the error after take-off and act very strange.

My question of flying home is in line with OP original where he asks if salvageable ... which for me indicates desire to get it home !!

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Nigel_
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solentlife Posted at 2018-7-13 01:34
I have not said conversion to True from Magnetic ... that's a totally different ball game and I agree with you is unnecessary.

What we do have though is a Flight Controller and Digital Compass that interact to give a directional reference. Then GPS position data repeated can then be used to 'fly home' autonomously.


"Its my question and always has been - if the machine is powered up and then gives an Error ... where does it get the information from to decide its an error ? It must have a programmed reference. Whether that's from previous calibration or actual programmed in data ... it has to have something to compare."

There are a few things that could trigger the error, eg:
  • Magnettic field is 3x stronger than the Earths magnetic field should be,
  • The relative strengths of the horizontal and vertical components of the magnetic field are nowhere near correct for the latitude reported by GPS.


The direction of travel shown by the GPS coordinates not matching the compass is an obvious one, but that can also be caused by wind so unless it can determine the wind direction and speed it is not possible to use this one.  It can guess the wind direction from the angle it has to fly, but I doubt it is very reliable and turning GPS off has to be done reliably.
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solentlife
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There are a few things that could trigger the error, eg:
Magnettic field is 3x stronger than the Earths magnetic field should be,
The relative strengths of the horizontal and vertical components of the magnetic field are nowhere near correct for the latitude reported by GPS.


Which brings me to the suggestion that it has a reference programmed in. Without such - none of those can trigger a warning.

The direction of travel shown by the GPS coordinates not matching the compass is an obvious one, but that can also be caused by wind so unless it can determine the wind direction and speed it is not possible to use this one.  It can guess the wind direction from the angle it has to fly, but I doubt it is very reliable and turning GPS off has to be done reliably.


Arrrrr this is a common error made by people to think the Drone flies same as a fixed wing machine. It does not. The Fixed wing machine has to point nose up into wind to counter wind drift as it flies a course, it has to YAW to counter the wind drift ... but a Drone does not. Because it flies by act of 4 or multiple propellors. The Flight controller alters the thrust accordingly to add a side motion component into the forward movement. It does NOT YAW up into wind as a fixed wing does. Its effectively giving side stick command to counter. It is not giving YAW as we would on a plane.
Therefore GPS course and Compass course subject to variation / deviation as per normal should tally even when flying in cross wind.

OK - turning GPS off ?? That actually does not happen. What happens is GPS MODE is disengaged ... the Flight Controller is still receiving whatever GPS data is available. You can still receive GPS coordinates in ATTI mode when GPS Mode automatically cuts off. (Note I am not talking about you manually selecting ATTI or P-ATTI as some call it - I am talking about Compass failure and machine automatically drops to ATTI). There are circumstances where GPS can still provide a path home ! Check the manuals.

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