Current measurement with a AttoPilot 90A

I’ve noticed an amperage mismatch from what a multimeter displays with what an AttoPilot 90A shows through Mission Planner. I can’t comment on 3DR’s Power Module because it didn’t have the voltage range on the first boat, and the second one I choose to try a PX4 instead of an APM2.6.

As best I can tell, this is attributed to the fact that the AttoPilot is ranging from 0-3.3V, while the code has INPUT_VOLTAGE set to 4.68 in config.h. Does anything else rely on INPUT_VOLTAGE or is it a different issue altogether? Thanks

Multimeter FMS
0.3A 0A
1A 0A
1.5A 0.01A
2.0A 0.35A
2.5A 0.9A
3A 1.4A
3.3A 1.8A

Have you seen how to use the AttoPilot current sensor in this wiki: … nt-sensor/
Also, this wiki gives you a basic idea on how to use the MP to setup the sensor: … -with-apm/

Thanks. Yes, I’ve seen both pages.

Upon further research, it appears I have a ~1.5A offset between what a multimeter measures and what the FMS records from the AttoPilot. While I can change the slope of the line via the Amps_per_Volt variable, there is no way currently to shift the line up to reasonably match. Basically I can’t find a way to change the ‘b’ value in y=mx+b, only the ‘m’ term with Amps_per_Volt.

Unfortunately I have also not been able yet to get data above 4A because loading the motor up to its normal 35-40A requires river testing (the fun of boats…) and a higher capacity current meter. But I’m also not looking for high accuracy current data, just a reasonable approximation.