"Generally, the rotational speed of a
DC motor is proportional to the voltage applied to it, and the
torque
is proportional to the current. Speed control can be achieved by
variable battery tappings, variable supply voltage, resistors or
electronic controls. The direction of a wound field DC motor can be
changed by reversing either the field or armature connections but
not both. This is commonly done with a special set of
contactors (direction contactors)."
Click
here to learn more.
"The classic
DC motor has a rotating armature in the form of an
electromagnet. A rotary switch called a
commutator reverses the direction of the electric current twice
every cycle, to flow through the
armature so that the poles of the electromagnet push and pull
against the permanent magnets on the outside of the motor. As the
poles of the armature electromagnet pass the poles of the permanent
magnets, the commutator reverses the polarity of the armature
electromagnet. During that instant of switching polarity,
momentum keeps the classical motor going in the proper
direction"
Click
here to learn more.
.gif)