Toothed gear type rotary engines consist of a concentric
rotor-stator assembly with small appendages (teeth)
extending from the rotor that mesh in receptors located
in the stator. The arrangement is similar to the layout of
a sun gear (rotor) and planets (receptors) except that the
teeth are not necessarily continuously spaced around
the rotor. The rotor and receptors are synchronized so
that a tooth meshes with a receptor as the rotor passes
it. The space between the teeth and the receptors
define the varying working volume. The area of the
exposed rotor face varies as it rotates through its cycle.
The shape of the rotor and receptors is designed so that
a net positive force is applied to the rotor faces, resulting
in a torque applied to the output shaft.