Electric Motor

Objective

The objective of this experiment is to demonstrate how electricity can be used to make a motor. This helps us to see how electrical energy is converted into mechanical energy. It also allows the user to see a practical application of electromagnetism.

Materials

Several feet of wire
Empty spool of thread
Two strong permanent magnets
Pencil
Two identical nails
Electrical tape
1 ft by 1 ft board
Aluminum Foil
6 Volt Battery

How to Build It

Sharpen a long pencil at both ends. This will serve as our rotor axle. The spool should fit perfectly around the pencil. Take the two nails and tape them, point to head, around the pencil. Wrap the wire around the nails as shown in the diagram. Pay close attention to the direction the wire is wrapped around the nails. The spool will be our commutator. The aluminum foil should be prepared in the following way. It should be fit in two strips around the spool. Each strip should be exactly the same length. The strips should be approximately one-eighth of an inch apart. Before taping the aluminum to the spool, strip the wire ends which are wrapped around the nails and place them on opposite sides of the commutator as shown in the diagram. The ends stay in place better if placed beneath the foil. Align the one-eighth inch separations with the nails before securing them to the commutator. The sharpened pencil ends will serve as makeshift bearings for the rotor. Make small indentations in two pieces of wood that will support the rotor and allow it to spin freely. There should be as little friction as possible. The rotor should spin several times with only a slight push.

electric motor diagram
[Source: Kadesch]


Up until now, our instructions have followed the diagram. In order to produce an easier to assemble and more functional motor, we will now vary from the diagram. The leads to the commutator should be as shown in the diagram—facing directly upward, and slightly touching the aluminum foil. Instead of connecting these leads to the other nails, simply connect them directly to the terminals of the battery. The permanent magnets replace these nails.

electric motor picture

Experiment

Attach the leads to the battery as shown in the diagram. Hold the two permanent magnets about one centimeter away from the ends of the nails on the motor when they are parallel to the ground. If offset a little bit, the motor should start to work on its own. If not, it could require a small push to get it going. The motor should now run smoothly as you hold the magnets in their proper position.

Troubleshooting

If there does not appear to be any current through the motor, try the following:

  1. Try holding a small paper clip or other small metal object close to the ends of the nails. If there is a current flowing, then the nails should act as electromagnets.
  2. Check the leads to commutator to see if they work. This can be done with a multimeter, or any device which allows you to see if current is present. You could attach the leads to a small light bulb, or even to an electromagnet. This should tell you if you have current passing through the motor.
If it appears that there is no current through the motor, you probably have a break in the circuit. Check the wire ends, which are connected to the aluminum foil, to see if they are still connected. Make sure that some of the exposed wire is in contact with the aluminum.

If there is current in the motor, but the motor still will not run, try the following:

  1. Spin the motor manually. If it does not spin very well, then there is probably too much friction. Try laying the pencil ends across some other object in order to get better spin and less friction.
  2. Hold the magnets at slightly different angles. Try holding different sides of the magnets to the motor. Experiment with different angles and pole combinations.
  3. Make sure that the breaks in the aluminum foil are aligned with the nail ends.
  4. Give the motor a good push to start it spinning.
  5. Make sure that your battery is not drained because it has been attached to the circuit for too long.
  6. Try a more powerful battery. This can be done by connecting several batteries in series with each other.
Questions for Thought
  1. What makes the motor run?
    ANSWER: The coils around the nails attached to the shaft of the motor act as electromagnets. The leads to the commutator send current running through the wires wrapped around the nails, and convert those nails into electromagnets with poles. Each electromagnet has either a north or south pole at its end, depending on the direction of the current. When the spin of the motor causes the wire lead on one side of the commutator to come in contact with the other strip of foil, the current changes direction. This is why during half of its turn the electromagnet on one side of the nails is attracted to the permanent magnet, and during the other half it is repelled. This attracting and repelling action is what causes the motor to spin.
  2. How can I make the motor spin faster or slower?
    ANSWER: In order to make the motor spin faster or slower you must increase or decrease the strength of the magnetic field. This is done by either changing the amount of current running through the motor or varying the distance of the permanent magnets from the motor.

Additional Information


ASU Department of Electrical Engineering
Last Updated: June 21, 2002
Original Page Development by: Matt Dayley and Keith Holbert
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