After reading the story about Kohei Minato’s super-efficient motor, reader Chris Drake wrote in with this explanation:
All Minato’s power calculations appear to be wrong (apparently it’s a common mistake many scientists make); you can’t measure input power using a multimeter when the current drain isn’t constant. You can see his workshop in his videos – all his calculations are done using common multimeters and a desktop calculator.
Minato motors use an optical sensor to “switch on” the “stator” (electromagnet) for a fraction of each RPM, so he’d need an oscilloscope and some funky math to figure out how much current the motors are really sucking up (or a stopwatch; and wait for the driving battery to go dead, then estimate based on the battery capacity).
It’s still a super neat idea though – which seems to boil down to “drive motors from the outside using aligned permanent magnets and momentary pulses from the stator” instead of the traditional “sick the stator in the middle” idea.
