Abstract: A modular, expandable, low-weight electric motor has a cylindrical, non-magnetic casing formed in axially-aligned sections. The casing sections are releasably connected to define a unitary structure with a polygonal exterior surface and a circular interior surface. Separate U-shaped stator pole assemblies are releasably mounted against the exterior of the casing, each casing section carrying the poles associated with a different motor phase. The poles extend through apertures into the interior of the casing, and have active pole faces which are curved and substantially flush with the circular interior surface of the casing. A modular rotor is mounted in the interior of the casing and carries magnetic elements in axially spaced-apart sets corresponding to each motor phase. The active faces of the magnetic elements are curved and oriented in a cylindrical arrangement.