Close Call/ Help Needed!

Here's my report on Healthy Drones. The compass says it was fine, but you can see it changing to ATTI mode all by itself a bunch of times on the Notifications tab. The RC said Compass Error in RED. But the healthy drone report doesn't reflect that kind of error. Pretty strange. The other strange thing in the report is it implies I did an assisted take-off, stating that I was in assisted take-off mode. I never do that, in fact I have never done that. This report says that ATTI mode started from the beginning, however I know the RED error message didn't show up until I got out about 250' or so. It was GREEN SAFE TO FLY for at least the first 200' out from take-off point. I was flying FPV when I saw it go from GREEN to RED. I never took my eye off the screen from when I got 10' off the ground till it went into ATTI mode, at which time I turned around and immediately landed VLOS.

When you play the flight back in the DJI Go app is the orientation correct? If you have not made too many flights the .dat file might still be on the phantom. It has way more info in it than the .txt file.
 
More like gusting wind, something that makes the rotational rate of the z-axis gyro not match the change in yaw reported from the compass...
That is where the .dat file may tell us what really happened...
Windy conditions will not have any impact upon the compass readings.
Having a bad compass calibration giving compass data that disagrees with what the GPS reports is the cause.
This is a simple open and shut case as I explained above.
 
Windy conditions will not have any impact upon the compass readings.
Having a bad compass calibration giving compass data that disagrees with what the GPS reports is the cause.
This is a simple open and shut case as I explained above.

What would cause the compass to have an error for awhile and then start working again? I am just theorizing that inconsistent wind would cause weird movements of the Phantom that would create a mismatch between sensors, but I think we need more data to determine what really happened...

I am also remember a case @BudWalker mentioned where he thought something similar occurred

The .dat file will have the compass measurements along each axis....
 
A compass error isn't a problem with the compass - it's a problem with what the compass is detecting.
Read this post again ...
Close Call/ Help Needed!

Yeah, whatever, it had an issue that put it in ATTI mode for a bit and then it went back into GPS mode. If it was a bad compass calibration why was it fine before and after the event? My opinion is we need more data to see what happened.

What message do you think you will get if you unplugged the compass? What message do you think you will get if the compass does fail?
 
Yeah, whatever, it had an issue that put it in ATTI mode for a bit and then it went back into GPS mode. If it was a bad compass calibration why was it fine before and after the event? My opinion is we need more data to see what happened.
The compass doesn't bring up an error while it is close enough to the affected area where it was calibrated.
When it flies out of the area and is now in the earth's normal magnetic field, >>Compass Error<<
This happened first just 57 feet from home.

What message do you think you will get if you unplugged the compass? What message do you think you will get if the compass does fail?
If the compass is disconnected, you get Compass Error and you can never recalibrate it, the compass data showing in the app will be zero.
But unless you break a wire or pull the connection, this will never happen in flight.
You should not think of a compass error as a failure of the compass.
The compass is working just fine but it's sending data that disagrees with what the the GPS is giving - because it's been given a bad calibration.

This is a really common error.
Compass calibration is important and it should only be done somewhere clear of magnetic influences.
Get a good compass calibration and stick with it. Don't go giving unnecessary recalibrations and introducing the risk of a bad one.
 
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The compass doesn't bring up an error while it is close enough to the affected area where it was calibrated.
When it flies out of the area and is now in the earth's normal magnetic field, >>Compass Error<<
This happened first just 57 feet from home.


If the compass is disconnected, you get Compass Error and you can never recalibrate it, the compass data showing in the app will be zero.
But unless you break a wire or pull the connection, this will never happen in flight.
You should not think of a compass error as a failure of the compass.
The compass is working just fine but it's sending data that disagrees with what the the GPS is giving - because it's been given a bad calibration.

This is a really common error.
Compass calibration is important and it should only be done somewhere clear of magnetic influences.
Get a good compass calibration and stick with it. Don't go giving unnecessary recalibrations and introducing the risk of a bad one.

Why did compass error go away as it drifted farther into the earth's normal magnetic field?

I agree not to do unnecessary compass calibrations. GPS and compass data would be difficult to compare to each other as GPS does not report any orientation data and compass does not report any position data, they compliment each other, which is why you need both for RTH and GPS mode. In the overall flight system comparisons could be made between the two with additional sensor data...the gyroscope and compass have readings that are the most similar and easiest to compare. Gyroscope measure rotation around each axis and compass measures heading...
 
GPS and compass data would be difficult to compare to each other as GPS does not report any orientation data and compass does not report any position data
The compass can report that the Phantom is traveling north.
And the GPS knows where it is and where it was and calculates that it is traveling 30° off north, the Phantom can't reconcile the data it's getting <Does Not Compute>
To deal with this it switches into atti and ignores the GPS input.
The flight record shows it doing this three times.
 
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The compass can report that the Phantom is traveling north.
And the GPS knows where it is and where it was and calculates that it is traveling 30° off north, the Phantom can't reconcile the data it's getting <Does Not Compute>
To deal with this it switches into atti and ignores the GPS input.
The flight record shows it doing this three times.

The compass can only report that it is facing north. The wind could be pushing it in any direction that the GPS would detect as a change. For example, the phantom could be facing north into the wind and the wind could be pushing it south. The GPS and accelerometer would detect this and the phantom would pitch down to compensate and hold position. The wind could also push it east, west, or south....this would all be normal operation, with GPS and accelerometers detecting the change in direction and the compass only reporting the direction the phantom is facing...

If however the z axis gyro detected that the phantom was rotating counterclockwise but the compass was reporting that the phantom was turning north to east then those sensor readings would not line up.
 
If however the z axis gyro detected that the phantom was rotating counterclockwise but the compass was reporting that the phantom was turning north to east then those sensor readings would not line up.
In the event of a bad compass calibration, it could be the accellerometers (rather than the GPS) that are disagreeing with the bad compass data but this will have nothing to do with the wind and would show up on a perfectly calm day just as well.

A compass error isn't indicating a compass malfunction.
It's indicating that the compass has detected a problem with the magnetic environment.
In this case it's that the compass calibration was bad so that when the Phantom flew away from the magnetic distortion and into clean air, it could tell that it's compass data was screwy (due to it having been calibrated in a bad location).
 
No ... Phantoms work just fine in windy conditions every day
Whatever the wind does to the Phantom, it has no influence on the compass sensor.
It just keeps reporting the orientation of the Phantom.

A compass error isn't indicating a compass malfunction.
It's indicating that the compass has detected a problem with the magnetic environment.
In this case it's that the compass calibration was bad so that when the Phantom flew away from the magnetic distortion and into clean air, it could tell that it's compass data was screwy (due to it having been calibrated in a bad location).

What? You said the compass could tell that the phantom was traveling north to compare against GPS. I said the compass can only tell that it was facing north, not traveling north...agree/disagree?

An example, phantom is hovering with no wind facing north in ATTI mode. The wind starts blowing from the north at 10 mph. Don't you think the phantom will drift south?

Now, same case in GPS mode, the phantom GPS and x axis accelerometer will detect the south movement and the phantom will react by pitching forward until x acceleration is zero and GPS is at the same point. This is normal and it will hover in place...agree I hope.

Finally, now imagine a case where a wind front is coming in, let's say you are hovering in GPS mode no wind facing north the wind ramps up quickly from 0 mph to 20 mph from the North. As the initial wind comes in the x axis accelerometer will see the acceleration and GPS will see the movement and phantom will pitch down to react; however since the wind is changing and increasing the phantom stills moves south. If the change in wind is rapid enough it could be moving south faster than initial movement despite the phantom's attempts to fly north. So now the phantom reacted to GPS south movement by trying to fly north per the compass but GPS is saying it is going farther south. Don't you think a situation like this could trigger a short term compass error? Once the wind stabilizes everything should return to normal....but for a moment the phantom is trying to fly north but is going south because the wind is changing ....

That is not even what I am saying happened here, just that we don't know. How do you know the compass calibration wasn't perfect and he flew into an area of interference that he then flew out of versus having a bad compass calibration and flying into an area of a normal magnetic field....

The .dat file would likely reveal all....
 
I don't know what happened with this flight. @TheRealNick is right, we need the .DAT to know more. But, the following could be relevant.

The P3s (in fact, any quad copters) flight controller uses a model to predict its orientation based on sensor data, pilot inputs, etc. What can happen is that the predictions made by the flight control model can disagree with the values actually measured by the sensors. There are three error terms (errorX, errorY, errorZ) in the .DAT that represent the discrepancy between the model predictions and the measured sensor data. When these errors get large enough the P3 switches to ATTI mode.

When the P3 says "compass error" it's really saying that the compass data doesn't agree with the model. This could happen if the compass data is actually inaccurate. But, it can also happen when the flight control model is affected by inputs it can't model. You can get a "compass error" by holding the P3 and waving it around (with the motors off!). The compass isn't broken. It's just that the model can't predict which way you're going to point the P3. Gusty wind conditions can also cause a "compass error" since the model can't predict the wind speed and direction. I analyzed a flight where this happened. RC Groups - View Single Post - Official Phantom 3 Professional / Advanced ***Owner's Thread*** First post has FAQ In this case the gusts were pretty intense; it doesn't sound like that was the case with this flight.

It seems that often the statement is made that a "compass error" was caused by a bad calibration. It may be true in some cases, but there really isn't any way to know this. The most that can be said is that the compass data doesn't agree with the flight control model.

Although the error terms have been labeled errorX, errorY, and errorZ it's not clear if the error terms are related to the X, Y, and Z axes; they may be related to roll, pitch, and yaw.
 
I'm having trouble keeping up with the complicated nature of the discussion.
I've conceded that it's probably the acellerometers/IMU rather than GPS that is disagreeing with the compass data - check my edited post above.
... Don't you think a situation like this could trigger a short term compass error? Once the wind stabilizes everything should return to normal....but for a moment the phantom is trying to fly north but is going south because the wind is changing
No I don't.
The compass keeps accurately reporting the orientation of the Phantom regardless of wind, angles or anything else.
The combined data from all sensors usually matches but when the compass calibration is screwed up this is the result.
The only thing that will cause a compass error is either a bad compass calibration or flying into an area with a distorted magnetic field.
At the height that the Phantom was flying (260 ft), it is more than unlikely that the Phantom detected a genuine magnetic anomaly.

This is a scenario that gets reported every week and I've given the simplest and most likely explanation of what happened and why.
 
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Once, I got the error it switched to ATTI mode. I tried to control it and that is pretty much when the wind picked up a bit. From what I can remember, either it swapped or I swapped it back to P-Mode in hope of correcting it. That is when I didn't take any chances and hit the RTH. The first time I hit RTH, it did not seem to respond but a second time it worked.

I have been digging in the .csv file and see a hint about switching into GPS mode, did you flip the function switch at some point? Maybe not, I am not as familiar with the .txt files as the .dat... It kind of looks like:

you flew up to max height
you flew down some
you starting flying out
it went to atti mode briefly
you hit RTH
you flipped switch to ATTI
you flipped switch back to GPS
you hit RTH
it went to atti mode briefly
you hit rth and the rest went normal

Below is a screenshot of the flight...

flight path.jpg
 
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How do you know the compass calibration wasn't perfect and he flew into an area of interference that he then flew out of versus having a bad compass calibration and flying into an area of a normal magnetic field

I am curious about this point. I had a similar issue. I calibrated at a good location middle of the desert. nothing metal around flew a number of flights on the calibration without any issues. No ATTI switches or other wonky issues. I then went to a new location. flew two batteries without an issue. The third battery I flew from the same take-off spot but I flew in a different direction. Got about 900 meters out BAM Compass Error.. I switched to ATTI flew back and landed without a problem. Folks in here said that it was a bad calibration. I don't follow the logic. It would appear to me that the calibration was fine. I just flew over a spot in the desert where there was interference..

Can someone explain why in the scenario I described that a bad calibration was the issue and not some anomaly where the Phantom was when I received the error.
 
I am curious about this point. I had a similar issue. I calibrated at a good location middle of the desert. nothing metal around flew a number of flights on the calibration without any issues. No ATTI switches or other wonky issues. I then went to a new location. flew two batteries without an issue. The third battery I flew from the same take-off spot but I flew in a different direction. Got about 900 meters out BAM Compass Error.. I switched to ATTI flew back and landed without a problem. Folks in here said that it was a bad calibration. I don't follow the logic. It would appear to me that the calibration was fine. I just flew over a spot in the desert where there was interference..

Can someone explain why in the scenario I described that a bad calibration was the issue and not some anomaly where the Phantom was when I received the error.

What was the wind like? Like @BudWalker stated if you jerk the Phantom around holding it with the motors off you can cause a compass error, I think gusty conditions would do the same thing or my example earlier when the Phantom tries to move in one direction but because of a sudden change in wind speed it actually moves in a different direction, that would cause a mismatch of the sensors. I know the Phantom is very impressive with wind, I fly in wind all the time, but I can not say I fly often in gusty wind or wind that is rapidly changing direction. I bet a Phantom in a tornado would have a compass error message....

The .dat file will show exactly what the compass sensor was reading at the time of the ATTI switch....
 
I hope you are able to figure this out from the .dat file. I have been testing the compass and wanted to know what the x, y and z where about. I've read here that mod should be around 1400.
So far, and I have more testing to do, I found that the compass reports the axis to the processor
and that when the aircraft is level the y ( value in sensors of the Go app) is zero(or close) when pointed north or south .
So pointed north , y=o, x= + 400 to 500, z=around 1300, mod around 1400
south y=0, x= -400 to -500, z and mod are same
east y= -400 to -500, x=0, z and mod are same
west y=+400 to 500, x=0, z and mod are same
Now what has been suggested might be a clue as when the aircraft is pitched the numbers all change in a strange way.
I wondered why we needed to point the nose down during calibration and it seems to record in the z axis.
I wonder if the pointing down angle is a bit more critical than it seems?
Is it possible if when doing the calibration we hold it down ,not at exactly a straight down angle but slightly off we record an error in the calibration data that doesn't show up except in specific pitch conditions?
It's unflyable with the weather we have next few days but I'll test as soon as I can.
 

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