Among the parameters offered by the ALT-S Plug-in is BATT_CRT_VOLT.
I had that parameter set to “0” but the Plug-in specified it should be “14.”
With my 4S battery, I far exceeded this voltage as I prepared for a test flight - but with that value set, the copter would not arm because of error of voltage below the critical voltage failsafe.
I reset it to “0” at the field, and was able to arm and fly normally.
My BATT_ARM_VOLT remained as it was - “14.7”
Reading the description of the BATT_CRT_VOLT parameter in the docs, I don’t understand why I should have gotten this error.
Is it possibly a bit in the ArduCopter 4.1 firmare? Or some other factor I’ve yet to discover?