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M600 Near-crash due to serious drift in airpressure altitude values
1201 10 2018-2-19
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cs_
lvl.1
Switzerland
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Hi all,

Today, I did a mapping flight with DJI GS and a Matrice 600 Pro. In the mapping area, there is an obstacle with a hight of 25 meters above ground with an additional elevation difference of 3 meters in comparison to my start point (measured with an RTK GPS). I therefore performed the flight at 31 m in relation to the starting point, to have a safe distance of 3 m to the obstacle. To be super save, I did a preliminar test flight with a Phantom 4 Pro with exactly the same flight plan, and it went perfectly, I had plenty of space between the P4P and the obstacle.

So I took of with the M600. Shortly after takeoff, I realized that the M600 was way below the programmed flight height and therefore the upper edge of the obstacle, and could stop the M600 in the literarly last second before crashing into the obstacle. I flow it manually back to the starting point (exact same position as takeoff), and realized that the indicated height was obviously wrong (10 m height indicated while hovering shortly above ground). Back in the office, I checked the flight logs and realized a tremendous drift in the air pressure altitude measurements (more than 8 meters during flight, more than 10 meters while standing on the takeoff point).




Now the question:
  • anybody else having similar issues, and if so,
  • is this a thing we have to deal with, or a guarantee claim?
  • is there a possibility to check stability of telemetry values before takeoff?

Thanks in advance for any help,
Cheers,

cs_
2018-2-19
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DJI-Mark
Moderator

United States
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If you are getting a different reading on the Phantom 4 Pro, you may want to refresh your firmware as well as reset to factory settings on your Assistant 2 Software. Please check also any type of compass calibrations to make sure you are getting an accurate reading. If the issue continues, please contact Customer Service to have a technician look at your aircraft.
2018-2-20
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cs_
lvl.1
Switzerland
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Hi,

Thanks for the reply, although I would have appreciated an answer which goes beyond the usual "please do a firmware update" scope.

I recently did some testings on the ground:
- For the first run, I took the M600P out of my office and switched it on so that it was still at room temperature  at t=0
- For the second run, I left the M600P for 2 h outside in the cold without power supply and then switched in on using a battery pack that was in my office before

The readings between the two setups differ largely:


My impression is that the sensors may warm up if in use, leading to the dramatic drift of 25 m (red lines). Nevertheless, the other setup also led to a drift of the sensors, readings did not stabilize before 10 minutes!

I'll write the DJI support...
2018-3-1
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cs_
lvl.1
Switzerland
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Answer from the support:

''
1. The barometer always drift automatically because of the barometer sensor noise. this is inevitable.
2. The P4 is seems to work more perfect than M600. The reason is that P4 has vision system, that helps P4 to be more accurate.
3. P4 and M600 are different model. wich means they have different sensors.
5. we suggest to install D-RTK module to improve accuracy of the M600 system.
''

My personal summary: Don't trust your M600 barometer altitude readings! My best practice is currently to let the system adapt after power-on for approx. 5 mins. on the ground, then start, fly at destination height, and then check whether the altitude is reasonable or not! The issues are not completely gone, but more rare.

Cheers
_cs
2018-4-3
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dsenechal
lvl.2
United States
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Spend $4500 for the D RTK, in addition to the cost of the M600, so it will be as accurate as a P4. Gotta like the way they think.
2018-4-24
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laurilah
lvl.1

Finland
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Hey

I am fighting with totally same problem. We are seen more than 20 m gap between planned altitude and real altitude, that is really bad because we scan forest in 50 meter and trees might be 30 meter high.

Is there any other solution than RTK?

Thanks  
2018-12-3
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rfAndy
lvl.4
Flight distance : 339542 ft
United States
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I thought all RTK gives you is less susceptibility to compass errors due to EMI.  So, even with RTK, I don't think it will give you any more altitude accuracy - at least how DJI uses it.  It only improves positioning and heading.  Perhaps a DJI admin/moderator will provide clarification on what you get with RTK??  Thanks for this info on M600, though.  I have one with RTK.  I'll have to find time to experiment.
2018-12-3
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laurilah
lvl.1

Finland
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Okay, so RTK does not give a straight solution.

Is there any reason why M600 Pro use only barometer to altitude measurement? Not GPS-data at all like other drones do. Or am I understand something wrong?
2018-12-4
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goldstar_456
lvl.1

Canada
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The very same thing happened to us with our M600 pros.
Right after updating the firmware, the reported AGL seemed to be 10-20 meters off the programmed ones during the first flight. This sofar has caused one crash and one near miss.

Not sure what is the solution, but we are planning on trying the RTK for now. Maybe rolling back to an older version of the firmware will help too, but I'm not sure how we can find the right firmware for this.

Let me know in case you found another solution.

Cheers,
2-26 12:54
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goldstar_456
lvl.1

Canada
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The very same thing happened to us with our M600 pros.
Right after updating the firmware, the reported AGL seemed to be 10-20 meters off the programmed ones during the first flight. This sofar has caused one crash and one near miss.

Not sure what is the solution, but we are planning on trying the RTK for now. Maybe rolling back to an older version of the firmware will help too, but I'm not sure how we can find the right firmware for this.

Let me know in case you found another solution.

Cheers,
2-26 12:55
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patiam
Second Officer
  • >>>
United States
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laurilah Posted at 2018-12-4 05:39
Okay, so RTK does not give a straight solution.

Is there any reason why M600 Pro use only barometer to altitude measurement? Not GPS-data at all like other drones do. Or am I understand something wrong?

Autonomous (non-differentially corrected) single-frequency GPS has a vertical accuracy of 10's of meters. For this reason, GPS is only used for altitude calculation in RTK-equipped DJI aircraft. Others use barometric pressure augmented with the aircraft vision and optical avoidance sensors if present.

So adding RTK to your M600 should give you higher accuracy and more stable altitude measurement so long as you maintain Fixed status. It won't, however gain you anything wrt the accuracy of your image geotags.
2-27 13:14
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