[ratdude747]

General rule of thumb for motors (at least what I was taught in college): A motor is most efficient when run exactly at the rated power output. More or less will result in a drop in efficiency. Obviously the latter is a better scenario than the latter, but in terms of % efficiency, all else being equal, going overkill isn't an improvement.

That said, it's far easier for a 2 cim drive to get pushed past the rated output, and given that batteries are usually recharged between matches, the time when efficiency (for realistic practical FRC purposes) counts is under full load (read: shoving match), so that's why a 2 cim drive will overheat and (probably) draw more amps in such a scenario.

The reason 6 cim drives lead to brownouts is not a motor issue per se; it's simply that such a drivetrain has more capability than a single battery can provide (at a voltage that the control electronics/VRMs can handle). So, realistically, in a FRC legal robot, you'll never see the full potential of a 6 cim drivetrain. You may see more than a 4 cim, sure, but you'll probably never get to full load simply because the battery can only give so much power (internal resistance is the limiting factor assuming good battery wiring). Hence the need for brownout prevention for such drivetrains.