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Motors
The DC (direct current) motor:
Motors are all about
magnetism. They use the
attractive and repellant forces
of opposite magnetic poles to
produce motion.
There are two types of
motors that we use today, DC
(direct current) and AC
(alternating current).
In this diagram there
is a DC motor similar to the
ones we built in class and is
mainly made up of six parts: a
field magnet, an armature, an
axle, a commutator, two
brushes, and most importantly
a DC power supply (e.g. a
battery).
http://electronics.howstuffworks.com/motor.htm
Motors
The DC (direct current) motor:
How does a DC motor work?
First we must discuss its parts.
Field Magnet - basically just a permanent magnet
Armature - an electromagnet
If you were to take a horseshoe magnet and place a simple electromagnet (i.e.
a nail inside of a closed coil hooked up to a battery) between it’s poles so that
the like poles of the permanent magnet and electromagnet are aligned , and
make it possible for that nail to pivot, what do you think would happen?
The nail will turn until it aligns its south
pole with the field magnet’s north pole and
its north pole with the field magnet’s south
pole, but will go no further than that. We
can only continue the rotational movement
if we change the direction of the flow of
electrons by reversing the battery
connections. This “flips” the electric field
of the electromagnet causing another
repulsion and attraction between the poles
of the two magnets, pushing the nail
around again to complete the circle.
Motors
The DC (direct current) motor:
Now, how can we flip the magnetic field without disconnecting
then reconnecting the battery between half turns?
In this image is the armature,
commutator, and axle. The
armature takes the place of the nail
in the previous example. It consists
of two metal plates joined together
by a coil wrapped around them.
Between the two plates is the metal
axle, just a metal rod that will be
placed on supports to allow
movement of the armature.
The metal commutator (in this diagram it is the broken green cuff
around the axle) is connected to the ends of the wire wrapping the
armature. All of these pieces form an open circuit containing only the
electromagnet. The brushes are the parts used to close that circuit.
Motors
The DC (direct current) motor:
In the diagram on the
right the brushes are indicated
in red. Each brush is hooked
up to opposite battery ends.
As the brushes come into
contact with the commutator
they form a closed circuit and
generate a magnetic field in
the armature causing it to turn.
After it makes a half turn, the
commutator comes into
contact with the brushes again,
only in the opposite
connection, which reverses the
magnetic field. The result of
this repeated process is
rotational motion and thus the
motor works!
Motors
The DC (direct current) motor:
Another explanation…
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/mothow.html
DC Motor
Right hand rule:
The Index finger points in the direction of the current;
Middle finger points in the direction of the magnetic field (N to S);
Thumb direction indicates the direction of force.
Motors
The AC (alternating current) motor:
“An important change came in the later 1880s and 1890s,
when electric power companies began considering the switch to
alternating current. Alternating current was perfect for the
distribution of electric power over long distances, and it worked well
with the Edison electric lamp, but no practical AC motor existed until
the works of Galileo Ferraris in Italy and Nikola Tesla in the United
States. Tesla’s contributions are remembered today more than
Ferraris’ in part because Tesla was subsequently hired by the
Westinghouse corporation, which used his patents along with many
others to become one of the major producers of electric equipment.
With a suitable AC motor available, AC power took off. It is still in
use today.”
http://www.ieee-virtual-museum.org/collection/tech.php?id=2345794&lid=1
Motors
The AC (alternating current) motor:
An alternating
current (AC) is an
electrical current whose
magnitude and direction
vary cyclically, as
opposed to direct current,
whose direction remains
constant. The usual
waveform of an AC
power circuit is a sine
wave, as this results in
the most efficient
transmission of energy.
City lights viewed in a motion
blurred exposure. The AC
‘blinking’ wave causes the lines to
be dotted rather than constant.
http://en.wikipedia.org/wiki/Alternating_current
AC Motor
AC Generator
AC Induction Motor (more efficient)
Motors
Here are some fun websites to go to!
To see animation and explanation of basic motors go to:
http://www.ieee-virtual-museum.org/collection/tech.php?id=2345794&lid=1
To see animation and information on how transistors (require an AC current to
increase or decrease voltage within circuits) work go to:
http://micro.magnet.fsu.edu/electromag/java/transformer/