There are many different types of permanent-magnet DC motors. They can be
classified according to their field systems, armature structures, and
arrangements of brushes and commutator.
The motor displayed on Figure 1 below is a Philips Group
P.M.D.C. motor disassembled from the Sinclair C5 motor
Figure 1
Below is a description for the motor components:
ROTOR: the rotating part of the motor which carries the field flux and
interactive current to create the torque. Torque acts on the rotor due to its
relation to the external magnetic field. Just as the magnetic field of the
rotor becomes fully aligned with the external magnetic field, the direction of
the current in the windings on the armature reverses, thereby reversing the
polarity of the rotor's electromagnetic field. A torque is once again exerted
on the rotor, and it continues spinning.
FIELD COILS: coils wound around the rotor. Field coils transfer the current
from the brushes and commutator to the rotor.
BRUSHES: The part of the motor through which the electrical current is
supplied to the armature from a power supply. They are generally constructed of
graphite or precious metal. Direct current motors have one or more pairs of
brushes. Figure 1 brushes, one is connected to the positive
terminal of the power supply and the other to the negative voltage input. The
brush connected to the negative voltage input is not visible but is identical
to the positive terminal.
COMMUTATOR: The part which is in contact with the brushes. The change in
direction of current is facilitated by the commutator. The brushes remain
stationary, but they are in contact with the armature at the commutator, which
rotates with the armature such that at every 180° of rotation, the current in
the armature is reversed.
LONG BOLTS: There are two parallel long through bolts which hold the motor
together.
PLASTIC SLEEVE FINGER ASSEMBLY: Is used to close the left end of the
cylindrical housing, is not of uniform thickness and this allows the motor to
be rotated in its circular clamp to adjust the final drive belt tension.
VENTILATED END CAP: The part which houses the brushes and. However it is
wise to be sealed because motors tend to contain interference-causing radio
frequency noise that would otherwise escape through the ventilation holes.
STATOR (permanent magnets): The stationery part of the motor. The part of
the motor which provides the magnetic flux needed for creating a torque. The
field system consists of two permanent magnets and a cylindrical housing
forming a part of the stator.
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