IMU Not behaving correctly.

[rszemeti]

IMU would know where magnetic north is and where
gravitational force is directed.
What it doesn’t know how you installed it
and oriented relative to boat body.
So you need to do calibration type ‘boat is leveled’
and you need to enter offset for heading
using regular compass (IMU doesn’t know where your bow is)

The way pypilot is written after doing it
you need to wait (was it couple minutes)
before restarting pypilot or pi
because pypilot saves calibration that infrequently.

You also need to check permissions on file system
that PyPilot actually can save calibration file and that it’s
not read-only for it.

Yes, done all that.  The Boat levels fine, angles seem correct for pitch and roll.

Yes, I set the compass offset.

I assume PyPilot will issue some sort of warnig if it can't write the calibration data.   I've no idea where it stores it, but this is a standard OpenPlotter install, no fiddling, I assume that OpenPlotter has the directory structure and permissions set up correctly, I could check, but not sure where it stores the cal stuff, any clues?

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There may be something wrong with your sensors

mobile phones do not manage this.  I am not sure what you refer to but you can hack in other algorithms, the point is, the phones do not calibrate in a way that gives better accuracy, you probably just have unusable sensors

Are pitch and roll really near zero under alignment?  Could there be any potential magnetic distortions?

I don't think my sensors are faulty ... the pitch/roll seems to be correct.

The "green circle" appears to be correct in as much as it goes through 360 degrees when the boat is turned through a circle ... what seems to be wrong is that as the boat goes around the "green circle" the resolved vector is from the centre of the sphere to the point on the circle ... that would explain the restricted range.

My feeling is that green circle should be co-planar with the red circle, not at 90 degrees to it?   Is it normal for that green circle to display like that on the display?

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I know on the MPU9250 sensor I have the following notes in some Arduinio code I have used before:

  // Sensors x (y)-axis of the accelerometer is aligned with the y (x)-axis of
  // the magnetometer; the magnetometer z-axis (+ down) is opposite to z-axis
  // (+ up) of accelerometer and gyro!

Is it possible the sensor used on this board has some other convention?  It looks to me as if the magentometer of this IMU is not aligned as expected with the accelerometers ...

The sensor I have is the ICM20948, which is recommended with the MacArthur HAT, is it possible this sensor has a different relationship between the axes of the magnetometer and accelerometers to the 9250 sensor?