2022-09-29, 12:45 AM
Just back from a few days on the water so I took some readings comparing Pypilot compass with the existing Raymarine fluxgate while we were swinging on the pick.
Before we went I was able to update Pypilot to the latest from github without any problem, thanks Sean.
No problem in GPS mode, followed the OpenCPN course without any issue.
Compass calibration however is still non linear. I had done the imu calibration last week, set boat level and redid the compass calibration at the start of this trip, message was 'same as previous'. The data is not as complete as I would have liked, between the current and the wind some sectors do not have any records, however it is clear that there is a considerable problem in the calibration. In the attached data, I have listed the reading for each compass and calculated the implied adjustment. If the calibration was linear, the adjustment should be the same within the expected accuracy of the equipment. Clearly that is far from the case. Actual alignment adjustment was set to zero.
Some notes on the data. I was trying to read values on two instruments, physically separated, at the same time while both were changing, so there is an inherent error there. That given, there is a fair repeatability in the readings and the implied adjustment does vary in a reasonably smooth pattern. Some more data in the 120-270 deg range would have been nice as there is obviously a large change in the implied adjustment in this sector. Note that the data was not taken in the order it is presented. Readings were taken over 3 days in two anchorages when things were stable enough.
Possible reasons:
1. Faulty IMU. Possible but the readings are repeatable within the expected accuracy.
2. Poor Installation. IMU is on top of the RPi in a box separated from the motor controller. In any case, these readings were taken with the controller inactive.
3. Characteristics of the Adafruit Breakout. Could there be manipulation of the data before it reaches the RPi.
4. RTIMULib Handling of the ICM-20948. Doubtful.
5. Software with the ICM-20948. Doubtful. From the wiki notes this chip has been worked on previously.
My thought is to try to look at the raw data coming from the breakout using a separate program. This would require a repeat of the swing test to be comparable but a rotation test of the RPi would be a start. Adafruit have some sample programs, I will look at those.
John
Before we went I was able to update Pypilot to the latest from github without any problem, thanks Sean.
No problem in GPS mode, followed the OpenCPN course without any issue.
Compass calibration however is still non linear. I had done the imu calibration last week, set boat level and redid the compass calibration at the start of this trip, message was 'same as previous'. The data is not as complete as I would have liked, between the current and the wind some sectors do not have any records, however it is clear that there is a considerable problem in the calibration. In the attached data, I have listed the reading for each compass and calculated the implied adjustment. If the calibration was linear, the adjustment should be the same within the expected accuracy of the equipment. Clearly that is far from the case. Actual alignment adjustment was set to zero.
Some notes on the data. I was trying to read values on two instruments, physically separated, at the same time while both were changing, so there is an inherent error there. That given, there is a fair repeatability in the readings and the implied adjustment does vary in a reasonably smooth pattern. Some more data in the 120-270 deg range would have been nice as there is obviously a large change in the implied adjustment in this sector. Note that the data was not taken in the order it is presented. Readings were taken over 3 days in two anchorages when things were stable enough.
Possible reasons:
1. Faulty IMU. Possible but the readings are repeatable within the expected accuracy.
2. Poor Installation. IMU is on top of the RPi in a box separated from the motor controller. In any case, these readings were taken with the controller inactive.
3. Characteristics of the Adafruit Breakout. Could there be manipulation of the data before it reaches the RPi.
4. RTIMULib Handling of the ICM-20948. Doubtful.
5. Software with the ICM-20948. Doubtful. From the wiki notes this chip has been worked on previously.
My thought is to try to look at the raw data coming from the breakout using a separate program. This would require a repeat of the swing test to be comparable but a rotation test of the RPi would be a start. Adafruit have some sample programs, I will look at those.
John