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Avoid Crash Due to Compass Interference (preflight)
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hallmark007
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hope this can help some.

Tip To Help Avoid compass interference and crash.


1/ Never calibrate Compass unless prompted to.

2/ start AC leave until you receive enough gps lock ,

3/ if you get Compass interference turn off AC and move to another location,
without interference.

4/ In bottom left hand corner on your map you will see small red triangle, check to make sure that this triangle is pointing in the same direction (heading) as your AC, this will show good compass on the ground.

Raise AC to height of 8ft
Hover for 20 seconds
Fly forward 2ft
Backward 2ft
Left 2ft
Right 2ft
Up 2ft
Down 2ft
Yaw left
Yaw right
Each time returning to hover position
If you have a good horizontal each time, you will then know you have good GPS good IMU and good Compass, and your ready to fly.

This exercise takes less than 2 minutes and is worthwhile doing before every flight,


2018-8-31
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Mullheliflier
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Good advice Hallmark007
2018-8-31
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Mark_One
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For what it's worth I agree you 100%, already seen too many stories that ended badly which probably could have been avoided with simple pre-flight checks.
2018-8-31
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M2Wair
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It's a shame advice like this can't be put into a purely advice section on the forum. A 'read only tutorial' sort of section to allow new users and indeed experienced pilots refresh knowledge without being lost in multiple user posts. Perhaps the admins could consider this! The advice above could and will prevent flyaways, so we'll done hallmark excellent advice
2018-8-31
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Wachtberger
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Thank you for reposting this and I fully agree with John!
2018-8-31
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FlyDK
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Great post - Thank you hallmark.
2018-8-31
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rolling56
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I thought all of us already did this before flying? J/King I do similar voo-doo just to make sure everything is good to go. Should be in the manual but no one reads it anyway...
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Armazia
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rolling56 Posted at 2018-8-31 03:30
I thought all of us already did this before flying? J/King I do similar voo-doo just to make sure everything is good to go. Should be in the manual but no one reads it anyway...

Right, I think everyone with some common sense kinda does this. The tips are alright, but just too much.. Just make sure to calibrate your compass the right way (as shown above), and don't if you dont need to. Then make sure your aircraft goes the same way as you are controlling it.

Besides these tips you can still crash because you might have not taken off with enough sattelites, so you can still crash your drone without wanting it.
2018-8-31
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Mark_One
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rolling56 Posted at 2018-8-31 03:30
I thought all of us already did this before flying? J/King I do similar voo-doo just to make sure everything is good to go. Should be in the manual but no one reads it anyway...

What is this "manual" you speak of?
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hallmark007
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Armazia Posted at 2018-8-31 03:40
Right, I think everyone with some common sense kinda does this. The tips are alright, but just too much.. Just make sure to calibrate your compass the right way (as shown above), and don't if you dont need to. Then make sure your aircraft goes the same way as you are controlling it.

Besides these tips you can still crash because you might have not taken off with enough sattelites, so you can still crash your drone without wanting it.

Read point number 2.
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Hellsgate
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I agree with everything except #1.
You should never need to calibrate the compass at all unless you modify your drone in some way.( especially when prompted this is one of the worst things you can do)
And just to add to your list if you do see a compass error prior to taking off then shut everything down move away from that location then try again.
If you still recieve the same error then either try a new location or abandon the flight if after the third try you still recieve a compass error abandon the flight.
Do not fly your drone if ever you see a compass error.
If in flight and a compass error comes up land imeadiatly in a safe manner. The main point is to get the drone on the ground as soon as safely possible.
2018-8-31
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Armazia
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Taking off with 5-7 satellites might still result into a crash, even if you got a locked position. You might consider changing it to 'Wait till gps is locked with 11 sattelites", as this is what most people here recommend.
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hallmark007
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Hellsgate Posted at 2018-8-31 03:56
I agree with everything except #1.
You should never need to calibrate the compass at all unless you modify your drone in some way.( especially when prompted this is one of the worst things you can do)
And just to add to your list if you do see a compass error prior to taking off then shut everything down move away from that location then try again.

I have been saying exactly that for a long time now, but although it’s true, there is the simple matter, for instance with Mavic Air when it asks for calibration will absolutely not allow you take off until you preform calibration and good calibration won’t have any negative effect on your drone, but my advice would always be check your compass levels in app before take off.

The only purpose of compass calibration is to measure the components of the aircraft's magnetic field so that they can be subtracted from the total measured magnetic field. Rotating the three-axis magnetometers allows the aircraft's flight controller to separate the surrounding magnetic field from the magnetic field of the aircraft itself. It's able to separate them since the aircraft's magnetic field remains constant (in the frame of reference of the magnetometers) while the surrounding magnetic field rotates.
2018-8-31
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Hellsgate
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hallmark007 Posted at 2018-8-31 04:12
I have been saying exactly that for a long time now, but although it’s true, there is the simple matter, for instance with Mavic Air when it asks for calibration will absolutely not allow you take off until you preform calibration and good calibration won’t have any negative effect on your drone, but my advice would always be check your compass levels in app before take off.

The only purpose of compass calibration is to measure the components of the aircraft's magnetic field so that they can be subtracted from the total measured magnetic field. Rotating the three-axis magnetometers allows the aircraft's flight controller to separate the surrounding magnetic field from the magnetic field of the aircraft itself. It's able to separate them since the aircraft's magnetic field remains constant (in the frame of reference of the magnetometers) while the surrounding magnetic field rotates.

I dont own an air and have never flown one so i cannot comment on those.
But your post is not aimed only at the mavic air thus a general rule of thumb should apply.For instance if a mavic pro or phantom pilot sees a compass calibration error the worst posible thing they can do is to calibrate it.

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hallmark007
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Armazia Posted at 2018-8-31 03:59
Taking off with 5-7 satellites might still result into a crash, even if you got a locked position. You might consider changing it to 'Wait till gps is locked with 11 sattelites", as this is what most people here recommend.

You need 6 sats to fly your drone, your drone receives both glonass and gps signal, so if you wait for 11 sats then you are guaranteed at least 6 gps or 6 glonass, there is also other factors regarding gps , which would take to long to explain in this short preflight.
However I do emphasize the need to spend some time at very low altitude to check your craft is safe to fly.
Many crashes occur because users just flying straight up and off and something happens and it makes it so much more difficult to get craft back on the ground.
2018-8-31
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GaryNash
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You cant buy experience, Great advice
2018-8-31
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hallmark007
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M2Wair Posted at 2018-8-31 02:54
It's a shame advice like this can't be put into a purely advice section on the forum. A 'read only tutorial' sort of section to allow new users and indeed experienced pilots refresh knowledge without being lost in multiple user posts. Perhaps the admins could consider this! The advice above could and will prevent flyaways, so we'll done hallmark excellent advice

Well hope it helps some.
2018-8-31
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hallmark007
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Mark_One Posted at 2018-8-31 02:39
For what it's worth I agree you 100%, already seen too many stories that ended badly which probably could have been avoided with simple pre-flight checks.

Thank you hope it helps.
2018-8-31
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HedgeTrimmer
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We disagree on #1.  I have never seen any problem or fallout from calibrating compass(s) when not prompted.   
2018-8-31
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Kingram
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Good advice Thanks now what about IMU calibration tips ?
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hallmark007
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HedgeTrimmer Posted at 2018-8-31 10:43
We disagree on #1.  I have never seen any problem or fallout from calibrating compass(s) when not prompted.

Then you haven’t been around long, many crashes I see start with the opening line , I calibrated my compass before I took off. Impossible to make a good compass better by calibration.
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hallmark007
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Kingram Posted at 2018-8-31 10:49
Good advice Thanks now what about IMU calibration tips ?

This is my view on IMU and calibration.

IMU "Inertial measurement unit" .

As far as I see it, IMU calibration on a level surface updates a table of values the flight controller software uses as a reference for a level stationary hover. From there the craft responds predictably to flight commands.  It also likely measures any sensor noise and thermal drift so that these technical imperfections are accounted for when using IMU sensor data in flight. - this is likely why there must be no vibrations during the calibration process.


Bad IMU calibration could cause drift and attitude issues as the flight controller fights to hold the craft in what it thinks is the correct attitude as opposed to the correct physical attitude.


The IMU usually has 2 types of sensors – angle and acceleration and in turn 3 sensors of each type measuring in the X,Y and Z axis. These sensors can, through vibration, aging, impact etc, drift in their response over time and thus an IMU calibration will establish a new reference for the IMU’s level/stationary state that the flight controller can work with to restore stable flight.


Think of calibration as the bringing back into line the measured craft attitude with the true physical craft attitude.


As to how often an IMU calibration is needed, Refer to your manual ; certainly after any impact or if there are suspicions the craft can’t hover in a level attitude in a windless environment.
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HedgeTrimmer
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IMO, #4 is an iffy check.   For sure, better than nothing.  

From reading about compass related crashes, the compass problems start when there is a deviation of around 25-degrees from actual.  That is about 1/16th of compass face.  90-degree being 1/4 and 45-degree being 1/8th.

The displayed red-triangle vs. direction drone is physically pointing is open to interpretation.  Leaving it vary hard to determine whether 1/16th (or 25 degrees) is being exceeded.

Be nice if RC gave a degrees heading which could then be checked against known direction.  Also be great for when GO-4 / Smartdevice go AWOL.
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hallmark007
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HedgeTrimmer Posted at 2018-8-31 11:03
IMO, #4 is an iffy check.   For sure, better than nothing.  

From reading about compass related crashes, the compass problems start when there is a deviation of around 25-degrees from actual.  That is about 1/16th of compass face.  90-degree being 1/4 and 45-degree being 1/8th.

If there is any deviation showing just move and see if it changes, there is also the option to check compass values in your app, I believe that most preflight plans will tell to check this, many don’t bother, but it’s a good indicator, compass whether drone or ships are extremely difficult to get 100% right because of everything at play, so this is why I recommend not just taking off and flying away, when compass clears any interference, it will be IMU that may show problems so the short exercise of up down back an forth etc should give good indication if IMU is off, if there was strong interference on the ground , you may just lift off and drone shoots off and nothing is going to save it then,
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hallmark007 Posted at 2018-8-31 10:53
Then you haven’t been around long, many crashes I see start with the opening line , I calibrated my compass before I took off. Impossible to make a good compass better by calibration.

I have not been around long, like some of dinosaurs.  

But I (as in myself) have not had any problems from calibrating compass regardless of no-prompting or false-prompting.
Got a lot of calibrating experience thanks to DJI's try this, try that, and GO-4 running on iPhone and iPad needlessly calling for  compass calibration.
BTW: For testing of calibrations, I have done upto four compass calibrations back to back to see if there was some significant changes between numbers shown for two compasses.  Have seen some minor changes in numbers (+/- 15), but nothing that jumped out showing potential for compass recalibration without prompting.


Guessing that those who have experienced crashes as direct result of calibrating their compass come down to one of two things:
1) bad field strength (XYZ) sensors (aka compass) - already have hardware problem with their compass
2) attempting to calibrate compass where calibration should not be done at all
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hallmark007
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HedgeTrimmer Posted at 2018-8-31 11:14
I have not been around long, like some of dinosaurs.  

But I (as in myself) have not had any problems from calibrating compass regardless of no-prompting or false-prompting.

Guessing that those who have experienced crashes as direct result of calibrating their compass come down to one of two things:
1) bad field strength (XYZ) sensors (aka compass) - already have hardware problem with their compass
2) attempting to calibrate compass where calibration should not be done at all


I think you said it yourself, many things can go wrong calibrating your compass.
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Montfrooij
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Very good advice!
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Kingram
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hallmark007 Posted at 2018-8-31 11:20
Guessing that those who have experienced crashes as direct result of calibrating their compass come down to one of two things:
1) bad field strength (XYZ) sensors (aka compass) - already have hardware problem with their compass
2) attempting to calibrate compass where calibration should not be done at all

If it ain't broke don't compass it , lol
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hallmark007 Posted at 2018-8-31 11:20
Guessing that those who have experienced crashes as direct result of calibrating their compass come down to one of two things:
1) bad field strength (XYZ) sensors (aka compass) - already have hardware problem with their compass
2) attempting to calibrate compass where calibration should not be done at all

I think you said it yourself, many things can go wrong calibrating your compass.

I believe same argument would apply to not calibrating IMU and VPS (forward & downward with Mavic Pro).  Both are dependent on humans.  IMU requires a level and flat surface.  The VPS needs a computer natively running Windows or Mac (no Virtual Machine based on problems I have read), with decent bright quality screen.


Yet we do calibrate IMU and VPS.  Even do IMU and VPS without being prompted too (often because of firmware updates, refreshing, and downgrades).

And if we can't make a calibrated compass more accurate, how can we make a calibrated IMU or VPS more accurate?  

Depending on how micro gyroscopes and micro accelerometers are made (type used by DJI) there may be little degradation over time.  For sure physics of inertia doesn't change.  Gravity does vary on earth, but it by so little as to be irrelevant to drone.  As for VPS, those should have no moving parts, only photon detecting sensors, leading to almost no degradation over lifetime of drone.

Whereas when we look at magnetic field sensors those are impacted by - changes to earth's magnetic field (over months), effects of our sun's magnetic field on earth, changes in location on earth being flown at.  Which would point to compass(s) needing calibration from time to time, when IMU and VPS would not.

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hallmark007 Posted at 2018-8-31 11:14
If there is any deviation showing just move and see if it changes, there is also the option to check compass values in your app, I believe that most preflight plans will tell to check this, many don’t bother, but it’s a good indicator, compass whether drone or ships are extremely difficult to get 100% right because of everything at play, so this is why I recommend not just taking off and flying away, when compass clears any interference, it will be IMU that may show problems so the short exercise of up down back an forth etc should give good indication if IMU is off, if there was strong interference on the ground , you may just lift off and drone shoots off and nothing is going to save it then,

If there is any deviation showing just move and see if it changes,

That is my point about 25-degrees or 1/16th on compass face.  The red triangle vs. direction drone is actually facing would make it very difficult to detect actual deviation.
Really need RC to provide us with compass reading in degrees.  From there, it would be possible to use drone's camera with cross hairs to point drone directly North or South or East or West.  Then verify with RC that compass is reading 0 or 180 or 90 or 270 degrees.  Only way to do that now would be through FlightLogs, which would be after the fact.

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hallmark007
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HedgeTrimmer Posted at 2018-8-31 13:44
I think you said it yourself, many things can go wrong calibrating your compass.

I believe same argument would apply to not calibrating IMU and VPS (forward & downward with Mavic Pro).  Both are dependent on humans.  IMU requires a level and flat surface.  The VPS needs a computer natively running Windows or Mac (no Virtual Machine based on problems I have read), with decent bright quality screen.

Again I feel your just trying to target everything I say, not to sure why, but I will put it to simple so you can understand.

There is no need to calibrate anything  unless it needs calibrating and calibrating something that is working as it should is not going to make it any better, I’m not now nor have I ever advised anyone to calibrate anything , unless they explained or showed symptoms of something not working correctly.
I posted this here to help people not to confuse them, and if it helps some as it obviously does judging by the posts then that’s why I posted, I have explained myself I don’t need to keep repeating, I have and do still use my advice for many years without problems, so what I know and say I don’t say lightly. It’s not going to help anyone trying to confuse them.
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GTstrudl
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I calibrate compass even not prompted to only when
1. The value of one of the compasses is much larger the the other but both of them still remain “green” in GO4
2. After calibration make sure both of campass values keep small

The reason for doing #1 is I suspect the random occurrence of message “aircraft disconnected” which only trigger in MP latest app/fw is cause by still not resolved program coding
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Hellsgate
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How about we all just agree to disagree about the compass calibration.
Those that want to calibrate there compass prior to every flight go ahead and keep doing it its your drone you can do what you like with it.
Me personally if i every see a compass error msg come up well then i know there is something wrong somewhere so i dont fly and i never recalibrate but thats me.

But here is a little bit of incentive for those that dont know what to do.
My boss calibrated his compass everytime he flew i had this same discussion with him but he chose to ignore my advice.
One day he took off as usual got up to about 10 meters switched over to sports mode and flew into a brick wall at over 60kph.
He no longer has a drone anymore.
We checked his flight log and yes he was prompted to recalibrate so he did. Little did he know that there was a car buried under his take off point.
So you guys go right ahead and keep recalibrating if you wish.
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hallmark007
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Hellsgate Posted at 2018-8-31 14:54
How about we all just agree to disagree about the compass calibration.
Those that want to calibrate there compass prior to every flight go ahead and keep doing it its your drone you can do what you like with it.
Me personally if i every see a compass error msg come up well then i know there is something wrong somewhere so i dont fly and i never recalibrate but thats me.

I have to agree with you, you can bring a horse to water but you can’t make him drink .
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Lonesome Crow
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Good recommendations.  I always turn my craft towards me to check out the forward sensors, you know, listen for that beeping warning.  And as a side note, verify the props are on securely.
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hallmark007 Posted at 2018-8-31 14:00
Again I feel your just trying to target everything I say, not to sure why, but I will put it to simple so you can understand.

There is no need to calibrate anything  unless it needs calibrating and calibrating something that is working as it should is not going to make it any better, I’m not now nor have I ever advised anyone to calibrate anything , unless they explained or showed symptoms of something not working correctly.

Hallmark007 - 1/ Never calibrate Compass unless prompted to.
Hallmark007 - Again I feel your just trying to target everything I say, not to sure why, but I will put it to simple so you can understand.
Hallmark007 - There is no need to calibrate anything  unless it needs calibrating and  calibrating something that is working as it should is not going to make  it any better

Several things Hallmark007;

If you are going to make big bold statements such as ''Never calibrate Compass ...''; expect people to disagree with you.  Simply because it is your position, does not mean it is right or only way things will work.   And if you are going to make such big bold statements, then be prepared for disagreemtent or to be challenged.


When you say you are only trying to help...   This is not first time you have posted that advice.  Ever heard of beating your own drum?
   05/14/2018 1/ Never calibrate Compass unless prompted to.
   07/11/2017 1/ Never calibrate Compass unless prompted to.

As for targeting you, your playing victim card is old and worn out.  Your accusation is also very hypocritical.  Being on more than one occassion you have trashed threads I and others have opened with nothing more than non-sense and insults.


Then there is your appeal plea that anyone who disagrees with you is trying to confuse others.  Such a plea means you got nothing to back you statement or position, thus the need to resort to an accusation.


Finally there is your condescending remarks - ''I will put it to simple so you can understand'', which is as old and worn out.  Understand this, you are far from an expert.


Other wise you would not have made such a statement as "There is no need to calibrate anything ... ... calibrating something that is working as it should is not going to make  it any better".  Various tools, instruments, including compasses are calibrated regardless of whether they are working or whether they appear to be in calibration.


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hallmark007
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GaryNash Posted at 2018-8-31 04:47
You cant buy experience, Great advice

Your welcome Gary, hope it helps.
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hallmark007 Posted at 2018-8-31 04:12
I have been saying exactly that for a long time now, but although it’s true, there is the simple matter, for instance with Mavic Air when it asks for calibration will absolutely not allow you take off until you preform calibration and good calibration won’t have any negative effect on your drone, but my advice would always be check your compass levels in app before take off.

The only purpose of compass calibration is to measure the components of the aircraft's magnetic field so that they can be subtracted from the total measured magnetic field. Rotating the three-axis magnetometers allows the aircraft's flight controller to separate the surrounding magnetic field from the magnetic field of the aircraft itself. It's able to separate them since the aircraft's magnetic field remains constant (in the frame of reference of the magnetometers) while the surrounding magnetic field rotates.

“for instance with Mavic Air when it asks for calibration will absolutely not allow you take off until you preform calibration”

One thing perhaps to consider with the Mavic Air, is to ensure it is sitting on ground in launch position when powered up.
I have seen a number of reports where Mavic Air is being handheld, and inverted when powered up. This seems to lead to a high number of “calibrate compass” requests from the Mavic Air. Most likely caused by the orientation of the hand held Mavic Air, or the GPS/GLONASS being blocked by hand.
Some have reported that this does make a difference to the rogue compass calibration requests on Mavic Air. But I have no way of testing the theory.
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hallmark007
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Aardvark Posted at 2018-9-1 02:28
“for instance with Mavic Air when it asks for calibration will absolutely not allow you take off until you preform calibration”

One thing perhaps to consider with the Mavic Air, is to ensure it is sitting on ground in launch position when powered up.

That may be true for some, while flying from locations I usually fly from , I don’t have any problem, if I move 5 miles down the road I get the message to calibrate, I have discovered if this happens that simply turning the craft off and back on the warning to calibrate goes away, I have tried this on several occasions and it seems to work, but only within short distance, I have yet to see if it works when travelling let’s say further than 50 miles.
2018-9-1
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Bob Brown
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Great advice. Reading the manual should be another good tip... it takes 15 minutes for most readers and can save you frustration and possible injury / stupid mistakes.
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