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Mavic 2 crashed; trying to learn/figure out why

Meta4

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Does this mean every time the aircraft is flown the compass and IMU have to be calibrated? Does the magnetization state of the air ever change or is it constant? If it changes, what cause the change?
It usually doesn't change unless changes are made to the drone, adding components etc.
The compass doesn't require recalibration each flight and the IMU is not sensitive to magnetic effects at all.
 

sar104

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Does this mean every time the aircraft is flown the compass and IMU have to be calibrated? Does the magnetization state of the air ever change or is it constant? If it changes, what cause the change?
As @Meta4 says, the magnetic state of the aircraft shouldn't change unless you add or change components or, perhaps, expose it to a strong magnetic field. Small changes in its magnetic state can be subtracted out by calibration. Big changes my require demagnetization of components first.
 
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2edgesword

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As @Meta4 says, the magnetic state of the aircraft shouldn't change unless you add or change components or, perhaps, expose it to a strong magnetic field. Small changes in its magnetic state can be subtracted out by calibration. Big changes my require demagnetization of components first.
If the artifacts are a product of some aspect of the aircraft why would they fluctuate versus being stead state?
 

sar104

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The graph in post #17 shows pulses at -130, -30, -20, +5, +50 of various magnitudes and durations.
The outliers simply occur at yaw values that the aircraft dwelled on, widening the statistical distribution on the ordinate. Don't forget that the bottom axis is not time, and so there is no duration information. The periodicity is with yaw, not time, and has a period of 2π (360°) which confirms that it is due to components of the magnetic field from the aircraft distorting the earth's magnetic field as the aircraft rotates.
 

2edgesword

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The outliers simply occur at yaw values that the aircraft dwelled on, widening the statistical distribution on the ordinate. Don't forget that the bottom axis is not time, and so there is no duration information. The periodicity is with yaw, not time, and has a period of 2π (360°) which confirms that it is due to components of the magnetic field from the aircraft distorting the earth's magnetic field as the aircraft rotates.
Thanks sar104. Is there any way to locate where on the aircraft the distortion is being generated based on the graph?
 

sar104

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Thanks sar104. Is there any way to locate where on the aircraft the distortion is being generated based on the graph?
Certainly not from that graph. From the three orthogonal magnetometer datasets one could approximately determine the strength and direction of the uncompensated magnetic field at the magnetometer, but that's not enough information to determine the location of the source. I'd probably try scanning the aircraft with a compass.
 

jbuy41

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What do I use to read my data file that I have uploaded to my PC from my iPad Pro. My mavic 2 went into the side of a water tower today. T he playback shows 96 '. Actual crash was much lower and why didnt OA work?
 

sar104

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Mike4884

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Sounds like a good plan. Might help you avoid some issues in the future.

Best of luck getting your issue resolved.

-Kale
Totally bad advice.... what he was doing was correct he doesn't need to calibrate all the time
 

Jorovi

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You need to look at the actual data rather than a summary to see the GPS health.
Click in the Download CSV on the Phantomhelp summary and go through the spreadsheet of data, looking at Column T "GPS Level"
That shows the drone having GPS Level1/5 for the first 40 seconds and dropping in and out of 1/5 many times during the flight.
It only had good GPS for the period 5:23-8:51 when it was above 400 ft and seeing more sky than it could down in the valley floor.
The period 19:16.6-19:20.7 is the one of concern.
Although the GPS receiver was getting signal from 8 sats but the flight controller had no confidence in the position data due to a poor satellite spread, multi-path issues or other factors.
Although it had not officially dropped into atti mode, the flight controller was aware of errors in the GPS data and had the lowest confidence level in the data, as it had for several other parts of the flight.

Flying in a poor GPS reception area as you were, it's a good idea to look at the number of bars shown next to the satellite icon on your display for an idea of how reliable GPS is.
I am a newbi studying this case and would like to know how I go about finding the "Column T "GPS Level"" I downloaded the flightrecord file then clicked on the DOWNLOAD CSV but the column on the spreadsheet does not reflect a column T with a GPS level only a column with GPS and the number of GPS satellite. Appreciate your advise. Thank you.
 

Jorovi

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Disregard, I was able to download and "see" the data....question seems like column T reflects GPS status level from 1-5. but noted than even with 8 satellites level of GPS can be 1 to 4 ! So how dio I interpret this ? also what is the minimum number of GPS satellites one must have to be safe and avoid these problems? Thanks again for your advises.
 

Meta4

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but noted than even with 8 satellites level of GPS can be 1 to 4 ! So how do I interpret this ? also what is the minimum number of GPS satellites one must have to be safe and avoid these problems? Thanks again for your advises.
It's not that simple.
It depends on the spread of satellites to give good angles for position calculation.
If the sats are all in a line or all clustered, you don't get a reliable position fix.
But the drone and app help you by giving an indication of how good the position data it gets is.
See the number of bars beside the number of sats on your phone or tablet.
 
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sar104

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Disregard, I was able to download and "see" the data....question seems like column T reflects GPS status level from 1-5. but noted than even with 8 satellites level of GPS can be 1 to 4 ! So how dio I interpret this ? also what is the minimum number of GPS satellites one must have to be safe and avoid these problems? Thanks again for your advises.
That's a measure of overall confidence in the FC's navigational solution - not just an HDOP or similar.
 

Jorovi

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That's a measure of overall confidence in the FC's navigational solution - not just an HDOP or similar.
Thank you for the explanation.....learned something totally new and what to watch out for....
 

AMann

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It's not that simple.
It depends on the spread of satellites to give good angles for position calculation.
If the sats are all in a line or all clustered, you don't get a reliable position fix.
But the drone and app help you by giving an indication of how good the position data it gets is.
See the number of bars beside the number of sats on your phone or tablet.
So true, I was hiking through a slot canyon and tried to get a position fix with my GPS. There were enough satellites but PDOP was high because the satellites were grouped in a narrow line. The next time through there, I got a good fix but realized later it was way off by over 100 meters! I think we were also dealing with a lot of signal bounce in the granitic bedrock of the canyon.