Slotted vs. Slotless Brushless Motor

Two brushless-motor designs distinguished by whether the stator core is slotted where the windings sit.

The common slotted brushless motor winds its coils around teeth on a slotted stator core. That concentrates the magnetic circuit, giving strong torque at low cost, but as the rotor magnets sweep past the teeth and slots the magnetic reluctance changes, producing cogging torque — a faint catch-and-release feel, most noticeable at low speed. A slotless motor instead builds the windings into a self-supporting coil that sits against a smooth, toothless core; with no teeth, cogging torque nearly disappears, so rotation feels smooth and low-speed control is fine-grained. The tradeoff is a wider air gap, meaning lower torque for a given size and a higher price. Dexterous hands and precision camera gimbals, where smoothness matters most, often use slotless or coreless motors; leg and foot joints, which need high torque, usually stay with slotted motors.

ExamplePrecision pan-tilt camera mounts that need smooth, jitter-free motion at low speed often choose slotless motors to avoid the cogging-torque catch.

Also called

Slotted BLDC Motor, Slotless BLDC Motor

Related

Cogging Torque · Brushless DC Motor · Coreless Motor · Permanent Magnet Synchronous Motor (PMSM) · Torque Density

Sources

Cogging torque - Wikipedia
Brushless DC electric motor - Wikipedia