Brushes: are housed in the brush holder and connected to the end cover. It is
made up of Carbon for small DC machine. For large DC machine, electrographite is
used to make brushes. A spring keeps the brushes pressed on the commutator
surface.
The current is conducted from the voltage source to the armature by the carbon
brushes which are held against the surface of the commutator by springs. They
are made of high-grade carbon steel and are rectangular.
Commutator and brushes:
Physical connection to the armature winding is made through a commutatorbrush arrangement. The function of a commutator, in a dc generator, is to collect
the current generated in armature conductors.
Whereas, in case of a dc motor, commutator helps in providing current to the
armature conductors. A commutator consists of a set of copper segments which
are insulated from each other. The number of segments is equal to the number of
armature coils. Each segment is connected to an armature coil and the
commutator is keyed (or fixed) to the shaft. Brushes are usually made from
carbon or graphite. They rest on commutator segments and slide on the segments
when the commutator rotates keeping the physical contact to collect or supply
the current.
Yoke:
The yoke acts as the outer cover of a DC motor and it is also known as the frame.
The yoke is an iron body, made up of low reluctance magnetic material such as
cast iron, silicon steel, rolled steel, etc.
Field Winding or Exciting Winding:
The pole is excited by a winding wound around the pole core. This winding is
called the Field Winding or Exciting Winding and made from copper. The number
of turns and cross-sectional of filed winding depends on the type of DC machine
as below:
 Large number of turns of small cross-sectional area is used for DC Shunt
machine.
 For DC Series machine, small number of turns of large cross-sectional area
is used.
 Both series and shunt field winding is applied for DC Compound machine.
 The connection of the field winding and the armature winding is done
according to the type of the motor and decides the characteristics of the
motor.
Armature Core:
 It is a cylindrical drum and keyed to the rotating shaft. A large number of
slots are made all over its periphery, which accommodates the armature
winding. Low reluctance, high permeability material such as silicon steel is
used for armature core.
BLDC
Primary efficiency is a most importent feature for BLDC motors. Because the rotor
is the sole bearer of the magnets and it doesn't require any power. i.e. no
connections, no commutator and no brushes. In place of these, the motor employs
control circuitry. To detect where the rotor is at certain times, BLDC motors employ
along with controllers, rotary encoders or a Hall sensor.
Brushless motor does not have any current carrying commutators. The field inside
a brushless motor is switched through an amplifier which is triggered by the
commutating device like an optical encoder.