Part 11

Take the armature off the motor and connect the commutator wires to a dry cell battery. Test the polarity of each end of the armature with a compass. Switch the connections on the commutator and test again. See how the compass needle changes direction?

With the armature still off, connect the field coil directly to the dry cell. Test the polarity of each end of the field with the compass. How can you reverse the polarity? Try it. It's easy.

Reassemble the motor again and start it. Push the field poles slightly out of alignment with the turning armature. What happens to the motor's speed? Can you tell why?

This time, push the field poles completely out of the way. Test the polarity of the armature as you slowly turn it by hand. Do you see what happens and why it does?

Try to reverse the direction of rotation of your motor by reversing the connections at the battery. What happens? Can you explain why?

Demonstrations You Can Give

Make a display board showing the parts of the toy motor and explain how each part works compared with the parts of a commercial motor.

For Further Information

There are several other types of toy motors you can build. Your club leader or power supplier can help you find information about them.

1. Did your toy motor run?

2. Did your motor speed up or slow down when you pushed the field poles out of line? Why?

3. What happens to the magnetic polarity of the armature when you turn it slowly by hand and check it with a compass?

4. How can you reverse the direction of rotation of your toy motor?

Is there another way too?

What is it?

LESSON NO. B-6

Credit Points 3

TAKING CARE OF ELECTRIC MOTORS

Through the magic of electric motors, much of our work is done faster and better at lower cost than we could do it without the help of the electric motor. People who use motors and treat them properly have much more time for other work and for leisure time activities. A 1/4-horsepower motor running quietly and steadily hour after hour will do the work of one man, and operate all day for about 5 cents without tiring. On many jobs it will work without "supervision", turning on and off automatically, as required. It does this on water pumps, in heating and cooling units, and on fans and similar appliances.

All that a motor needs to do its work is electricity and a little care. Let's see what you can do to give proper care to motors in your home and on your farm.

You'll Need

A light oil (SAE 10) for motors of less than one horsepower and a slightly heavier oil (SAE 20) for larger motors. See if you need grease for cups which may be on large motors. If so, be sure you use ball-bearing grease and not ordinary cup grease. Cotton waste or clean rags will be needed for wiping off the motors, and a tire pump or vacuum cleaner for blowing out the dust or dirt.

WHAT TO DO

1. First, make a list of all the electric motors that work for your home. You may wish to make a separate list for your farm buildings. You'll probably be surprised at how many there are. Don't forget the sewing machine, the refrigerator, the freezer, the vacuum cleaner and other small but important motors. Don't touch any motor that is running. Disconnect them before you touch them.

2. Make a motor service chart with columns headed: Use, Location, Horsepower, Volts, Amperes, Service Required, Date Serviced and What was Done. (See sample) Then list all the motors that require any servicing. Some will have the instructions on the motor or appliance; the instruction booklet that came with the motor or appliance will also tell what servicing is required.

Step 1. Plan the job. Start with the motors in the home. Then you can care for the motors on the farm.

Step 2. Be sure that any motor on which you are going to work is disconnected. Then wipe the outside case clean with a cloth. If the motor has openings in the end, use a vacuum cleaner to suck out dust, dirt or chaff. A tire pump may also be used to blow out this dirt. If you use compressed air, be sure the pressure is not high as it may damage wiring inside the motor. Dust-proof motors should be used in dusty or dirty places.

Step 3.