Can you imagine the multitude of uses for electric motors? We may even say "motors, motors, everywhere electric motors!" Electric motors are used in home, work, and recreation, silently doing work for us in converting electrical energy into mechanical energy! We see them in appliances such as vacuum cleaners, refrigerators, microwave ovens, computers, automobiles, and even toothbrushes. A VCR has several miniature DC motors, as do DVD and CD-ROM players. Other common uses are elevators, pumps, power tools, and manufacturing equipment. Electric motors have played a key role in exploration efforts deep into the sea and in space ventures. Do you remember the Mars Sojourner Rover? Or the current space exploration robots named Spirit and Opportunity? (Figure 1.) These space robots use miniature electric motors and servomechanisms as a means of propulsion and motion. These miniature motors are compact and powerful and require little energy to operate them. Surprisingly, there were 39 miniature motors on each of the Spirit and Opportunity rovers! There are many activities found in technology education classes that use miniature electric motors. The most common are robot experiments, activities, and projects along with solar cars, and LEGO activities. In most all of these activities the motors are direct current, permanent magnet motors.
[FIGURE 1 OMITTED]
While electric vehicles are not really a brand new idea, as they were invented in the early 1900s, we are seeing electric-powered vehicles in current model line-ups. With the increasing costs of gasoline and concern for the environment, several companies, such as Honda, Toyota, and Ford, have introduced electric vehicles. Honda has introduced a new hybrid Civic model that gets over 50 miles per gallon of gasoline by teaming up an electric motor with a gasoline engine to provide power to drive the car. Ford has introduced a hybrid electric SUV called Escape, as shown in Figure 2, that combines the performance of a gasoline engine and the economy of an electric vehicle.
[FIGURE 2 OMITTED]
Many of the electric motors that we commonly see and use are called "fractional horsepower" motors that are usually less than one horsepower. However, we may see very large electric motors that are rated in thousands of horsepower used in research and industrial applications. The National Aeronautics and Space Administration (NASA) uses very large electric motors, 40,000 horsepower, to drive compressors for its wind tunnels such as those found at the Ames Research Center. Yet they share a common principle of operation--using changing magnetic fields to produce mechanical motion.
History of Electric Motors
The invention of the electric motor is the result of a number of inventions and discoveries in the field of electricity during the eighteenth and nineteenth centuries. While "electricity" and "magnetism" and some of their properties had been known for many years, how to use them to produce mechanical motion was not. Several key discoveries were critical to the invention of the electric motor. These discoveries included the discovery of electricity, the battery, and the principle of electromagnetism. Perhaps we might say that the discovery of electromagnetism by Hans Christian Orsted in 1820 was a pivotal event that led to the development and invention of electric motors. He demonstrated that a wire carrying a current was able to deflect a magnetized compass needle. Orsted did not suggest any satisfactory explanation of the phenomenon, nor did he try to represent the phenomenon in a mathematical framework; however, other scientists and inventors would follow along with practical inventions that capitalized on electricity and electromagnetism.
Two of the more significant scientists and inventors were Michael Faraday and Nicola Tesla. Interestingly, Michael Faraday was apprenticed as a bookbinder at the early age of fourteen. …