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About IMU
1155 11 2018-11-11
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Monk32
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Flight distance : 50915 ft
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Hi. I have a question...my air's IMU2 shows a small part in yellow color permanently. The air flyies great without any problem. I had calibrate IMU but still remains as that. (Imu1 has a small green part).
Can someone explain that?
Thanks
2018-11-11
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AlexPapadas
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Good day,
I believe that the yellow coulor is the interference of the air. You may see this bar status changing while you move your air away from magnetic parts and other staff that can interfer with the IMU.
2018-11-11
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DeuceDriv3r
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that statement is wrong on many levels.

he is talking about the IMU not the compass since the air only has one.. it has to be the IMU

the IMU is not updated outside.. its done on a completely leveled surface, indoors, cooled to approximately 60 degrees according to DJI engineering and devoid of vibration ... magnetic interference has nothing to do with it

now to compass calibration .. that is done outside in an open area away from all metal and electrical interference that could disturb the compass....
2018-11-12
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Monk32
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Deucedriv3r..you have right. I am talking about IMU. Some times the IMU2 bar is completely empty. Does this means everything is ok? I am comfused.
2018-11-12
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DeuceDriv3r
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Monk32 Posted at 11-12 09:14
Deucedriv3r..you have right. I am talking about IMU. Some times the IMU2 bar is completely empty. Does this means everything is ok? I am comfused.

I don't have the air so I will get that out there BUT DJI products are very similar.. and I tend to read about all issues since its also widely speculated that DJI firmwares have very common code bases..

I have seen where IMU 1 and 2 will have different biases for both gyro and accelerometer and doing a cal will generally fix that..

if the bar is empty is it just a REAL small number or does it have a data label like error or no data?

there have been a few folks that have shown pictures of either a gyro or accelerometer going bad and showing a data error but didn't get a warning in the pre flight screen or status bar that an IMU was down or degraded.. DJI had them send it back in for that...?
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2018-11-12
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hallmark007
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Monk32 Posted at 11-12 09:14
Deucedriv3r..you have right. I am talking about IMU. Some times the IMU2 bar is completely empty. Does this means everything is ok? I am comfused.

Lower the better IMU warning will show up in your app if there is a problem.

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.

2018-11-12
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Monk32
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Deucedrv3r ...no. I have never see an error or data error problem report. Always i made a perfect flight. I just want to understand what is going on with indications.
2018-11-12
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DeuceDriv3r
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Monk32 Posted at 11-12 09:47
Deucedrv3r ...no. I have never see an error or data error problem report. Always i made a perfect flight. I just want to understand what is going on with indications.

just the 2 IMU values drifting in different directions as all. could be from any number of factors that involve MEMS accuracy and depending on whether DJI keep drift and filter tables could just be accumulated bias information..

personally I don't like it when the IMUs disagree and since I don't know what DJI use as limits to decide when the deviation is excessive and begin changing sources for navigation.. I don't like to let them wander too far..

just be sure when you do an alignment that you painstakingly level the surface and DJI recommends a pretty cool environment to do the alignment around 65 deg F

let the aircraft cold soak in that 65 deg room and try and start the alignment as soon as you get it up and running before it heats up too bad.. also run a gimbal alignment after the main alignment on the same level platform ...
2018-11-12
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Monk32
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Hallmark007 thanks. Normaly the IMU or an INS needs to get calibration every time before flight. Here there is no such need. Once after a small crash, or once every maybe...10 flights, a calibration is not a bad idea.
2018-11-12
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DeuceDriv3r
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Monk32 Posted at 11-12 10:00
Hallmark007 thanks. Normaly the IMU or an INS needs to get calibration every time before flight. Here there is no such need. Once after a small crash, or once every maybe...10 flights, a calibration is not a bad idea.

I would not to and IMU cal unless it was outside of excellent for more than a couple flights, the app tells you to or the aircraft isn't flying right personally ...
2018-11-12
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Monk32
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AlexPapadas thanks. Normaly the IMU is using a magnetometer unit. I don't think the air's IMU system is using it too. So I am not sure about interference problem in IMU. The factors changing IMU's state are some small crashes, thermic situations, some scale factor errors, misalignment errors, and accumulated errors through time. Here I am asking opinions about the indication state through the bars cause is difficult to understand the logic of the indicating situation. For example, what means if the bar is completely empty (no color indication and no data error report). Have a nice time!
2018-11-12
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Monk32
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Well...today i receive a "data error" message in screen of IMU.
IMU1 is working fine and air flyies perfectly.
Crazy cituation.
2018-11-13
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