Motor controllers are necessary with AC motors to supply the 3-phase AC that the motors need in sync with the motor's rotation. (DC motor controllers are simpl

Motor controllers are necessary with AC motors to supply the 3-phase AC that the motors need in sync with the motor's rotation. (DC motor controllers are simpler, but I don't think DC motors are used in any modern commercially-produced EV.) This generally requires some amount of software. The motor generally has current and voltage and RPM and temperature limits, and the motor controller keeps everything within those limits. But the motor controller isn't there just for that reason, it's there because the motor couldn't function without it. DC motors are different; those you could just literally replace your gas pedal with an on/off button and wire it straight from the battery to the motor. Not that that's a good idea.