From the App Note 9-axis MotionFusion and calibration algorithms document:
"Magnetic interference from external metal or magnetic objects will distort the output of the MotionFusion algorithm. A small magnetic interference may cause the compass value to deviate, creating a yaw error in the MotionFusion algorithm. A larger magnetic interference will trigger logic that detects such magnetic disturbances by comparing the compass data to the gyroscope data, and temporarily stops using the compass. The gyroscope can be relied on for short periods of time; however, if the magnetic disturbance remains for long periods of time, reliance on the gyroscope data will result in an accumulated error; when the magnetic disturbance disappears, there will be a noticeable settling artifact as the system recalibrates to the compass values."
I have several questions here:
1) What is the definition of "larger magnetic interference" that causes the system to stop using the compass data?
2) Is there any way to tell if the compass is in the "interference" mode?
3) When you say that the gyros can be relied on for "short periods of time" roughly how long is "short"? 5 seconds? 30 seconds? Several minutes?
4) How long does the system need to be free of magnetic disturbance before the compass is recalibrated?
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