Allowed scale factor minimum too strict for RM3100?

VDLJu · August 5, 2020, 10:06am

Hi,

I have seen high variation between RM3100 units on the magnetic field intensity. I have seen that the scaling factor was narrowed lately:

But soon later restriction was eased for RM3100. Only the maximum scale factor limit was changed.

github.com/ArduPilot/ardupilot

AP_Compass: revert change to RM3100 scale factor and increase scale limit

committed 05:06AM - 24 May 20 UTC

tridge

+8 -4

This reverts the change from #13895 and instead resolves the issue by increasing… the scale factor limit to 1.4 There is an open question as to why some RM3100 compasses show a different scale factor (by about 1.25 times) to other versions of the same sensor. As we haven't resolved this properly it seems the correct thing to do is follow the datasheet but allow for a wider range of scale factors to cope with the variation between sensors

I’m now facing an issue where the lower limit is too strict for RM3100.

… bad radius 394 expected 526

This would correspond to a scale factor of 0.749, which is a lot lower than the allowed 0.85. Although this specific unit gives this error message it seems to give sensible response/measurements.

I have done this testing with AC 4.0.3 and CUAV NEO v2.
I’m not able to calibrate that specific compass due the restriction and I expect that others having calibration issues with CUAV NEO V2 could be caused by the same reason.

VDLJu · August 5, 2020, 10:56am

I would suggest that the compass scale factors are re-evaluated.
I would recommend that for RM3100 the minimum should be set to 0.70