
Stepping Motor Systems 241
commutator or brushes: they are therefore robust and reli-
able.
The rotor is held at its step position solely by the
action of the magnetic flux between stator and rotor. The step
angle is a property of the tooth geometry and the arrange-
ment of the stator windings, and accurate punching and
assembly of the stator and rotor laminations is therefore
necessary to ensure that adjacent step position are exactly
equally spaced. Any errors due to inaccurate punching will
be non-cumulative, however.
The step angle is obtained from the expression
The VR motor in Figure 8.5 has 4 rotor teeth, 3 stator
phase-windings, and th ...