A permanent-magnet synchronous motor, driven by a servo drive that commutates it sinusoidally using position feedback. The rotor carries magnets rather than windings, so there is no rotor current and no rotor heating from slip, which is what gives the class its torque density and efficiency. The term AC refers to the drive waveform, not to it running from a mains supply directly.

Because it produces smooth, continuous torque rather than the torque ripple that simpler commutation schemes create. Smooth torque is what allows accurate motion at very low speed, good surface finish on machined parts, and quiet running. It requires higher-resolution feedback and more capable drive electronics, which is part of why this class costs more than simpler brushless motors.

The motor body is usually IP65 as standard, with higher ratings and shaft seal options for washdown and contaminated environments. Pay attention to the shaft seal specifically, since it is often rated separately from the body and is the usual point of entry for coolant and washdown water. Connector orientation and type also affect the achieved rating once installed.

They match the motor to the supply voltage and to the speed range required. The same frame can be wound for different bus voltages, producing different speed and torque characteristics from identical mechanics. Choosing the wrong winding gives a motor that cannot reach the required speed at the available bus voltage, or one that reaches it but produces less torque than expected at working speed.

Occasionally, but it is rarely worth it. The drive must support the specific feedback device and its protocol, hold the motor's electrical and thermal parameters for protection and tuning, and match voltage and current ratings including peak. Manufacturers sell matched pairs because the control loop depends on the combination. Mixing typically costs more in commissioning time than it saves in purchase price.

Standardised flange faces by frame size, with keyed shafts for positive torque transmission or smooth shafts for clamping hubs and shrink discs. Smooth shafts are preferred where backlash matters, since a key allows a small amount of lost motion. Check shaft diameter, flange pitch circle and pilot diameter against the gearhead or coupling intended, since these are standardised but not universal.

Work out the move profile first, then calculate the peak torque needed for acceleration, the root-mean-square torque across the whole duty cycle, and the maximum speed required. Peak must be within the motor's peak rating and the root-mean-square figure within its continuous rating. Check reflected load inertia against rotor inertia at the same time, since a motor that meets the torque figures can still be untunable if the inertia ratio is poor.