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Bashy
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This might be a stupid ask but, in the case of ''Fly aways'' from compass issues, why hasnt a failsafe been added to the coding, something like , if auto atti mode do not automatically apply motor speed, only use input from sticks, or, if magnetic interference detected, then hover unless input is from the sticks, you get the idea, i am sure theres a reason this hasnt been done, but there must be a way to prevent these compass ''Fly aways'' as they mostly stem from magnetic issues. Just a thought  at 5:30am is all
2018-7-10
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Geebax
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The trouble is, the aircraft does not necessarily know it is in trouble when there is a compass iszsue.
2018-7-10
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Mark The Droner
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My understanding is the AC will often do what it's supposed to do even if there is a compass error.  What happens depends on how far off the compass error is.  
2018-7-11
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Bashy
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Surely the AC shouldnt think that flying off at a rate of knots without stick inputs and when not in any intelligent mode is right?
2018-7-11
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Geebax
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Mark The Droner Posted at 2018-7-11 02:19
My understanding is the AC will often do what it's supposed to do even if there is a compass error.  What happens depends on how far off the compass error is.

That's my understanding too.
2018-7-11
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Geebax
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Bashy Posted at 2018-7-11 20:25
Surely the AC shouldnt think that flying off at a rate of knots without stick inputs and when not in any intelligent mode is right?

Maybe, but flying off without stick inputs is not necessarily a compass problem, most often it is a wind problem.
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Bashy
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But my question was about "fly aways" from a compass error ;)
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Geebax
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Bashy Posted at 2018-7-11 20:32
But my question was about "fly aways" from a compass error ;)

As far as I know, compass errors do not bring 'fly aways'. They produce eratic flying, that's all.
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Bashy
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It did to me, had there been an object close by it would have smashed the ac, i have also seen a few others on youtube, FB and  some on here too where compass error caused the ac to shoot off,
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Geebax
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Bashy Posted at 2018-7-11 21:57
It did to me, had there been an object close by it would have smashed the ac, i have also seen a few others on youtube, FB and  some on here too where compass error caused the ac to shoot off,

In order to fly away, the aircraft needs to have its motors running at differing speeds to produce flight in one direction, compass problems do not usually cause that. However a bad compass error will cause the aircraft to go into ATTI mode, and if there is wind around, then it will get blown away. As for reports of others having that happen, I am very skeptical of those reports, often the person reporting them did not really know what was happening at all. Even without going into ATTI mode, a bad compass error will cause the aircraft to fly in a different direction to that which the operator is trying to fly it.
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Bashy
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Im sorry but your take on this is wrong, i had a compass error that initiated ATTI mode and the the drone shot off to the left at speed, it was the motors that  that did this, not the wind, this is another example, clearly not the wind


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Geebax
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Bashy Posted at 2018-7-11 23:05
Im sorry but your take on this is wrong, i had a compass error that initiated ATTI mode and the the drone shot off to the left at speed, it was the motors that  that did this, not the wind, this is another example, clearly not the wind


OK, I'm wrong.
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KEJ
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Bashy Posted at 2018-7-11 23:05
Im sorry but your take on this is wrong, i had a compass error that initiated ATTI mode and the the drone shot off to the left at speed, it was the motors that  that did this, not the wind, this is another example, clearly not the wind


Out of interest from where you took off from anything obvious that may have caused it.

High power cables coming ashore under you, utility cables under the pavement or steel reenforcing on pier or ground etc.

I dare say you had the odd bead of sweat on your brow!

2018-7-12
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Bashy
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It was the 1 and only time i took off from my sunroof
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Nigel_
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Bashy Posted at 2018-7-11 20:32
But my question was about "fly aways" from a compass error ;)


I assume that it is because it uses the compass to maintain its heading and also to maintain its balance.  While it also has GPS, any movement due to compass error is corrected by it flying back to the correct GPS coordinates which you don't notice happening because the corrections are very fast and continuous, once GPS is off there is no longer a correction so the compass causes it to lean and leaning causes it to move.

Some people will argue that it uses a gravity sensor to maintain vertical, but I suspect any gravity sensor is going to be affected by vibrations and so instead it uses the compass which is not affected by vibrations and is also a very fast sensor that allows fast and accurate adjustment, it has to use the compass for the yaw correction since a gyro sensor will drift out of position over time while the compass doesn't, if you have to use the compass for keeping yaw then why not also use it for pitch and tilt?
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Nigel_
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Bashy Posted at 2018-7-12 01:00
It was the 1 and only time i took off from my sunroof

You need to use an old car that doesn't use electric motors with powerful magnets in the sunroof!
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Bashy
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Nigel_ Posted at 2018-7-12 01:09
You need to use an old car that doesn't use electric motors with powerful magnets in the sunroof!

Yeah  but then the oldies have steel body work which would cause an issue yeah?

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Nigel_
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Bashy Posted at 2018-7-12 01:13
Yeah  but then the oldies have steel body work which would cause an issue yeah?

Not a problem, before the days of electric sunroofs you could normally remove the sunroof from the car to have an open top, put the sunroof on the ground away from all the steel and use it as a launch pad.
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Aardvark
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Nigel_ Posted at 2018-7-12 01:07
I assume that it is because it uses the compass to maintain its heading and also to maintain its balance.  While it also has GPS, any movement due to compass error is corrected by it flying back to the correct GPS coordinates which you don't notice happening because the corrections are very fast and continuous, once GPS is off there is no longer a correction so the compass causes it to lean and leaning causes it to move.

Some people will argue that it uses a gravity sensor to maintain vertical, but I suspect any gravity sensor is going to be affected by vibrations and so instead it uses the compass which is not affected by vibrations and is also a very fast sensor that allows fast and accurate adjustment, it has to use the compass for the yaw correction since a gyro sensor will drift out of position over time while the compass doesn't, if you have to use the compass for keeping yaw then why not also use it for pitch and tilt?

"Some people will argue that it uses a gravity sensor to maintain vertical, but I suspect any gravity sensor is going to be affected by vibrations and so instead it uses the compass which is not affected by vibrations"

Is that not the job of the gyroscopes in the IMU ?

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Nigel_
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Aardvark Posted at 2018-7-12 03:42
"Some people will argue that it uses a gravity sensor to maintain vertical, but I suspect any gravity sensor is going to be affected by vibrations and so instead it uses the compass which is not affected by vibrations"

Is that not the job of the gyroscopes in the IMU ?

Gyroscopes measure acceleration/deceleration, they don't tell you which way up you are.  You can zero the values before takeoff and then keep track of the movements which will allow you to maintain balance for a while but you will get some drift over time.  If you also have a gravity sensor then the drift can be corrected, it can also be corrected using a compass, I think the Phantom uses the compass, maybe it is more accurate than a gravity sensor affected by a lot of vibration.
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Aardvark
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Bashy Posted at 2018-7-11 23:05
Im sorry but your take on this is wrong, i had a compass error that initiated ATTI mode and the the drone shot off to the left at speed, it was the motors that  that did this, not the wind, this is another example, clearly not the wind

https://www.youtube.com/watch?v=87qI0QcbPBw

That video is maybe not the best example, judging by the water surface there is a fair bit of wind at ground level, so higher up is likely to be far stronger.
Also he calibrated his compass instead of moving the aircraft away from the steel beams presumably used to build the dock. Not the best idea I would think.
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Bashy
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Its a good example cause he obviously caused the compass error, so it shows that the ac does in fact use its motors to fly off to another  location, this is what i am asking, if there was a way to add a failsafe so that if there is no input form the sticks, under this error, do not power up the motor, that sort of idea.....
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Aardvark
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Nigel_ Posted at 2018-7-12 04:02
Gyroscopes measure acceleration/deceleration, they don't tell you which way up you are.  You can zero the values before takeoff and then keep track of the movements which will allow you to maintain balance for a while but you will get some drift over time.  If you also have a gravity sensor then the drift can be corrected, it can also be corrected using a compass, I think the Phantom uses the compass, maybe it is more accurate than a gravity sensor affected by a lot of vibration.

"Gyroscopes measure acceleration/deceleration"

That would be the job of the Accelerometer in the IMU, not the gyroscope. The gyroscope would be used as the reference of what level is (After IMU calibration on flat surface), and the aircraft adjusts motor speeds to keep aircraft level.
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Nigel_
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Aardvark Posted at 2018-7-12 04:15
"Gyroscopes measure acceleration/deceleration"

That would be the job of the Accelerometer in the IMU, not the gyroscope. The gyroscope would be used as the reference of what level is (After IMU calibration on flat surface), and the aircraft adjusts motor speeds to keep aircraft level.

The accelerometers measure linear acceleration, the gyroscopes measure rotational acceleration.
The gyroscopes can't measure rotational position any better than the accelerometers can give you a GPS location, they can only guess it based on a known starting point and adding up all the movements.
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Aardvark
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Bashy Posted at 2018-7-12 04:08
Its a good example cause he obviously caused the compass error, so it shows that the ac does in fact use its motors to fly off to another  location, this is what i am asking, if there was a way to add a failsafe so that if there is no input form the sticks, under this error, do not power up the motor, that sort of idea.....

The aircraft in that video may well have switched to ATTI mode, in which case the wind would have taken it away. If the GPS is being ignored for positioning as it is in ATTI mode then the aircraft does not know what its position is, and it gets blown away. The problem possibly is that because of the conflict between mal adjusted compass and GPS heading that one of them is wrong, or they are both wrong. The aircraft would have no way of telling which was correct. So it does the best it can and hovers in the moving body of air around it. And the Go Pro 3 strapped below it probably does not help matters. Being a Phantom 2, it's likely that the technology has moved on quite a bit since then.

It would be interesting to see the flight record. Most of the comments on you tube seem to question the integrity of the video.

At least, that's my understanding of how it works.
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Aardvark
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Nigel_ Posted at 2018-7-12 04:27
The accelerometers measure linear acceleration, the gyroscopes measure rotational acceleration.
The gyroscopes can't measure rotational position any better than the accelerometers can give you a GPS location, they can only guess it based on a known starting point and adding up all the movements.

"the gyroscopes measure rotational acceleration."

Rotational position would be measured by the compass ?

As far as I'm aware the primary job of any gyroscope would be to set the level, an artificial horizon.  Depending on device it could also be used to set a heading if it were set up as a gyro-compass, but in the Phantom I don't think it's used for that.

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Nigel_
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Aardvark Posted at 2018-7-12 05:01
"the gyroscopes measure rotational acceleration."

Rotational position would be measured by the compass ?

Yes, rotational position comes from the compass, it is not just a horizontal compass but also measures the vertical magnetic field to give it the rotation around the 3 axis, it is being out in the vertical that causes the aircraft to fly off sideways in a magnetic field.

Gyroscopes maintain the level, but if you spin up a toy gyroscope you can set it up at any angle, it doesn't automatically go to vertical.   A gyro compass has to be zeroed regularly to keep it correct, which is exactly what the P4 does although I suspect it does it far more often than with an old aeroplane gyro compass otherwise we wouldn't get the compass problems, just inaccurate compasses.
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Bashy
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OK, lets forget that video and look at my incident when i took off from my sunroof, it ascended a few feet, then the compass error, then atti mode, then motors kicked in and it shot off to the  left, when i say shot off, i mean it went at some speed, the wind that day was calm, else i wouldnt have even tried taking off from the roof of the car.

Downside is, i cannot find the thread i started about it any where, not even searching google, its as if its vamoosed......
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Nigel_
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Bashy Posted at 2018-7-12 05:53
OK, lets forget that video and look at my incident when i took off from my sunroof, it ascended a few feet, then the compass error, then atti mode, then motors kicked in and it shot off to the  left, when i say shot off, i mean it went at some speed, the wind that day was calm, else i wouldnt have even tried taking off from the roof of the car.

Downside is, i cannot find the thread i started about it any where, not even searching google, its as if its vamoosed......

Maybe the reason it shoots off is that as soon as it is not flying level, it needs more lift to maintain height so the motors turn faster to generate the required lift.  Just like if a human trips then they tend to run to avoid a fall.
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Bashy
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no, i do not think that is the reason, it was more like it thought it should be elsewhere, this is the best i can do cause i do not have the flight log anymore, i was left  stick full right when it shot off, you can see it did a perfect semi

https://app.airdata.com/main?share=rClqFR
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Bashy
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Please do download the CSV and see what you can make of it.  That day the wind was from the north west, the ac shot off to the west, so it couldnt have been the wind.....
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Aardvark
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Nigel_ Posted at 2018-7-12 05:40
Yes, rotational position comes from the compass, it is not just a horizontal compass but also measures the vertical magnetic field to give it the rotation around the 3 axis, it is being out in the vertical that causes the aircraft to fly off sideways in a magnetic field.

Gyroscopes maintain the level, but if you spin up a toy gyroscope you can set it up at any angle, it doesn't automatically go to vertical.   A gyro compass has to be zeroed regularly to keep it correct, which is exactly what the P4 does although I suspect it does it far more often than with an old aeroplane gyro compass otherwise we wouldn't get the compass problems, just inaccurate compasses.

"Gyroscopes maintain the level, but if you spin up a toy gyroscope you can set it up at any angle, it doesn't automatically go to vertical."

Agreed, and that's what the IMU calibration on the level does, it gives the gyroscopes a reference level.
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Nigel_
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Bashy Posted at 2018-7-12 06:27
Please do download the CSV and see what you can make of it.  That day the wind was from the north west, the ac shot off to the west, so it couldnt have been the wind.....

It was in GPS_Atti for nearly all of that, still using the GPS to maintain location, so the high speed was caused by it trying to maintain its GPS location when the harder it tried the further it got from the target!  Because the compass was wrong it flew in the wrong direction requiring a continuous correction to the direction which resulted in it flying a circle.
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Bashy
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Yep, so you can see where a failsafe would be beneficial....
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Nigel_
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Aardvark Posted at 2018-7-12 06:28
"Gyroscopes maintain the level, but if you spin up a toy gyroscope you can set it up at any angle, it doesn't automatically go to vertical."

Agreed, and that's what the IMU calibration on the level does, it gives the gyroscopes a reference level.

The gyroscopes need to be zeroed every flight, and probably a lot more often than that.  An IMU calibration made 1 year ago is not going to work.   It can't do the same before takeoff because it is not necessarily taking off from level ground.

It may have a gravity sensor to do that, but gravity sensors will be affected by vibrations so the compass may be preferable.

Using a compass is not essential, some aircraft don't use one.
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Aardvark
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Nigel_ Posted at 2018-7-12 07:08
The gyroscopes need to be zeroed every flight, and probably a lot more often than that.  An IMU calibration made 1 year ago is not going to work.   It can't do the same before takeoff because it is not necessarily taking off from level ground.

It may have a gravity sensor to do that, but gravity sensors will be affected by vibrations so the compass may be preferable.

However the gyroscopes in the IMU do not need calibrating every flight, As far as I'm aware they detect the angle they are sitting at on the ground with reference to the IMU calibrated zero. To the point where the camera gimbal adjusts its position so that it sits level with horizon, where the aircraft might be sitting on a slight slope.
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Aardvark
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Bashy Posted at 2018-7-12 07:06
Yep, so you can see where a failsafe would be beneficial....

The failsafe is dual compass, dual Accelerometers and dual gyroscopes. But they only have one human (usually) :-)
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Anokadrone
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I plagiarized an article in Donezon.com but here is a summary of the devices the drone is using:

Three-axis gyroscopes measure rotation rate around, you’ve guessed it, 3 axes: roll, pitch and yaw.
The function of the 3D accelerometer is to measure the orientation of a drone relative to earth’s surface.

The combination of 3D gyro and 3D accelerometer allows a six-axis gyro to measure the amount of static acceleration due to gravity and also the amount of dynamic acceleration. These two measurements help us determine the angle the device is tilted and figure out the way the device is moving. These inputs are fed into the IMU and Flight controller and the Flight controller makes the decisions on how to change the motor speeds to accomplish the task at hand.
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Bashy
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Aardvark Posted at 2018-7-12 08:41
The failsafe is dual compass, dual Accelerometers and dual gyroscopes. But they only have one human (usually) :-)

The fail safes do not work if the drone flies off on its own, this is what I am asking, plus, they are hardware, I am on about some code, if sticks = central stay blooming put
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Aardvark
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Anokadrone Posted at 2018-7-12 08:56
I plagiarized an article in Donezon.com but here is a summary of the devices the drone is using:

Three-axis gyroscopes measure rotation rate around, you’ve guessed it, 3 axes: roll, pitch and yaw.

Thanks for the update, that makes some sense when all is linked like that.

Looks like its harder to get detail on DJI equipment than the real thing :-

https://www.bbc.co.uk/news/technology-44807091
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