An induction motor is very similar to a BLDC but instead of using permanent magnets in the rotor, there are coil windings which induce a magnetic field and then act like magnets. Control of the induction motor usually is AC and has a fixed rotational speed. If speed control is required a simple drive controller called a variable frequency drive can be used. This controller modulates the output frequency which varies the voltage on the windings. AC induction motors are simple to drive, but are usually heavier than BLDCs and physically larger, require larger gearboxes and have higher inertias. A stepper motor is also a brushless motor, but has quantized steps of rotation. The build of a stepper motor resembles that of a BLDC but typically has many more poles to enable very precise discrete stepping of the motor. The motor may also have additional phases for more precise control. Steppers are designed for discrete “steps” while a traditional BLDC is designed for continuous rotation. A stepper motor can also hold it’s position with high torque. Essentially a stepper is a BLDC with a defined control loop already in place to hold the motor at a particular angle (including hall effects and encoder feedback)
