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Basic Motor Theory -- An Illustration
Imagine a circle of people with their arms extended into the center of the circle. Now, put a person inside the circle standing on a floating platform. The single person wants to turn around but can't because the platform won't allow him to push on anything but the hands of the people in the circle. To keep from tiring himself out, the person in the middle reaches ahead of himself to pull and half of the time he reaches back to push.
Basic Motor Theory -- The Real Thing
The rotor of a motor is the person in the middle of the circle. The rotor is made of a small core with a length of wire wrapped around it. Most motors use alternating current. Alternating current changes direction 60 times a second in the United States. The field magnets around the outside of the motor are called stators and have fixed poles. Alternating current allows the rotor to change its magnetic charge from positive to negative. It has to change poles in order to keep traveling. It pushes against the negative pole with it's positive pole until it travels past it, then must switch to a negative charge to pull itself toward the positive pole coming up.
Basic Materials for Magnets
Field magnets come in four types; Neodymium magnets are made from neodymium, iron, boron and transition metals. They're strong for their size and look like metal. Neodymium magnets are found in microphones, servo motors, DC motors (such as car starter motors), and computer disc drives. Ceramic magnets consist of strontium carbonate and iron oxide. They're gray in color and are used in DC brushless motors, Magnetic Resonance Imaging or MRI machines and outboard motors. Samarium cobalt magnets are made of samarium, cobalt and iron. They're made from rare earth minerals and are found in sensors, linear actuators and satellite systems. Alnico magnets are composed of aluminum, nickel, cobalt, copper, iron and sometimes titanium. Alnico magnets are the most common. They're used in sensors, radars, holding magnets, coin acceptors, car parts, telephones and cow magnets. Cow magnets pick up metal on the ground before the cow can eat it.
Shapes of Magnets
Field magnets inside motors are shaped to fit into the motor's casing, lining it in segments that are square and curved. Rigid magnets come in horse-shoe shapes, cubes, bars, circles and discs. Magnets in odd shapes are familiar to everyone as refrigerator magnets. Strips or sheets of flexible magnet material is used in advertising, packaging and building trades.