A slotted motor has a stator with coils wound around iron teeth. The iron teeth are made of stacked laminations which help to reduce eddy currents that affect torque output of the motor. The iron core has an inherent attraction to the magnets of the rotor and cause a cogging effect that is most evident when the rotor is in motion at slow speeds. The amplitude of cogging is dependent on a few factors, including the slot-pole combination and skew of the stator stack or rotor magnets.
Slotted motors can be “wound-on-tooth”, which means copper is hand wound around each tooth to match the winding design, or “pre-wound” and stuffed onto the tooth. However, the most common method to wind a slotted stator is “needle wound”. This is a highly automated method and the most cost effective, but sacrifices copper fill.
Slotless motors have a stator and rotor like a slotted motor, but they do not have the same iron core that slotted motors have. Instead, windings are typically potted in an epoxy to hold the form. As a result of the iron-less stator, slotless motors are zero-cogging. While the torque output is comparatively lower to that of a same-size slotted motor, the zero-cogging design is ideal for pointing systems and other applications that require very smooth motion.
Additionally, the potted winding conserves space and allows for a larger inner diameter (ID) to outer diameter (OD) ratio. This allows for easier cable management and integration of brakes or other system elements in the through hole.
For more information on slotted motors verses slotless motors, read our Technical Paper ‘Comparison of Slotless and Slotted Motors’.
Agility™ Slotless Motor