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Read Ebook: Home-made Toy Motors A practical handbook giving detailed instructions for building simple but operative electric motors by Morgan Alfred Powell
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Ebook has 265 lines and 21830 words, and 6 pages
Home-made Toy Motors
Transcriber's Note
ARTS AND SCIENCES No. 9
Home-made
Toy Motors
A Practical Handbook Giving Detailed Instructions for Building
Simple but Operative
Electric Motors
A. P. Morgan
COLE & MORGAN, Inc.
P. O. BOX 473 CITY HALL STATION
NEW YORK, N. Y.
COPYRIGHT 1919
COLE & MORGAN, Inc.
Of course most experimenters have in all probability seen many electric motors, but it is more than likely that the exact operation is not thoroughly understood. Here is your chance to learn.
The little motors described in this book can each be made in two or three hours out of a few scraps of sheet iron, magnet wire and screws. The cost of the necessary materials is practically negligible.
One of the main advantages of these little motors is that they illustrate the actual principles that are used in the large motors, such as are employed everywhere for practicable power purposes.
The iron parts may be made out of sheet iron or the ordinary so-called "tin" used in cocoa cans, etc. Thin tin can be cut with an ordinary pair of shears. Sheet iron such as is used in making stovepipes, etc., is an excellent material to use in making these little motors. Sheet iron is usually heavier than tin and will have to be cut with a pair of "snips." Greater skill will also then be required in bending the parts. It is worth while noting however, that the extra difficulty involved in using the heavier material is worth the trouble because it makes possible a more powerful and efficient motor.
The first and easiest type of motor to make is the "Simplex."
If a wire, carrying a current of electricity is formed into a loop, the entire space enclosed by the loop will possess the properties of a magnet.
Electromagnets play a very important part in the construction of electric motors. The strength of an electro magnetic coil is proportional to its ampere turns. The number of ampere turns in a coil is obtained by multiplying the number of amperes flowing through the coil by the number of turns of wire composing it.
You can easily see the effect of turns of wire on an electromagnet by winding two or three turns of wire around a nail and connecting it to a battery. These two or three turns will probably create enough magnetism to enable the nail to lift up one or two ordinary carpet tacks.
Then increase the number of turns to forty or fifty and note that the magnetism of the nail has increased greatly and that it now possesses power to pick up a larger number of tacks at a time.
It will be found that the magnetism of an electromagnet is strongest at the ends. These places are called the poles.
One of the most important laws of magnetism is that like poles repel each other and unlike poles attract each other. A North and a South pole therefore tend to pull toward each other, whereas two North poles or two South poles repel one another.
Figure 6 illustrates the principle of an electric motor.
Each end of the armature winding is connected to one half of a brass ring called the commutator and marked "C, C," in the illustration. The two halves of the commutator are insulated from each other and are mounted on the armature shaft so that they revolve together with the armature.
The armature and the field are both electromagnets.
One brush is connected to one end of the field coil. The other end of the field coil and the other brush are connected to a source of electric current.
As soon as the current is turned on, the armature and the field both become magnets. The North pole of the field attracts the South pole of the armature and vice-versa. The armature starts to move so that the poles will come opposite but as the commutator moves around and is turned over, the current flows through the armature coil in the opposite direction. This reverses the magnetism of the armature and that which was the South pole become the North pole and vice-versa.
The armature poles will therefore have to move 180 degrees in order that the South pole may come opposite the North pole of the field. Before it gets there, however, the commutator will have turned over again, reversing the current in the armature and making it necessary to continue its journey again. This process keeps up and so the armature revolves always trying to seek a new position which it is prevented from remaining at by the action of the commutator.
Motors are said to be series or shunt wound depending on whether all the current flowing through the armature also passes through the field or whether it divides between the two as shown in Figure 7.
The Simplex Motor is an interesting little toy which can be made in a couple of hours, and when finished it will make an instructive model.
As a motor itself, it is not very efficient, for the amount of iron used in its construction is necessarily small. The advantage of this particular type of motor and the method of making it is that it demonstrates the actual principle and the method of application that is used in larger machines.
The field of the motor is of the type known as the "simplex" while the armature is the "Siemen's H" or two-pole type. The field and the armature are cut from ordinary tin-plated iron, such as is used in the manufacture of tin cans and cracker boxes.
The simplest method of securing good flat material is to get some old scrap from a plumbing shop. An old cocoa tin or baking-powder can may, however, be cut up and flattened and will then serve the purpose almost as well.
A piece of knitting-needle one and seven-eighths inches long is required for the shaft. Bind the two halves of the armature together in the position shown in Figure 9. Bind them temporarily with a piece of iron wire and solder them together. The wire should be removed after they are soldered.
Two small holes should be bored in the feet of the field magnet to receive No. 8 wood screws, the purpose of which is to fasten the field to the base.
The field and armature are now ready for winding. It is necessary to take proper precautions to prevent the first turn from slipping out of place.
The field should be wound first. This is accomplished by looping a small piece of tape or cord over it at the point indicated by "A" in Figure 15. The next two turns are then taken over the ends of the loop so as to embed them. Wind on three layers of wire on one side and then run the wire across to the other side and wind on three layers there. The third layer of wire in the second coil should end at "B." It should be fastened into position by a loop of string so that it will not unwind.
This method divides the field winding into two parts, both of which are connected together. The outside layer of the first coil is connected to the inside layer of the second coil. The two coils really form one continuous winding divided into two parts. After the winding is finished, give it a coat of shellac.
The winding of the armature is somewhat more difficult. The wire used for winding both the armature and the field should be No. 25 or No. 26 B. & S. Gauge double cotton-covered.
In order to wind the armature, cut off about seven feet of wire and double it back to find the center. Then place the wire diagonally across the center of the armature so that there is an equal length on both sides. Place a piece of paper under the wire at the crossing point to insulate it. Then, using one end of the wire, wind four layers on half of the armature. Tie the end down with a piece of thread and wind on the other half.
The ends of the wire are cut and scraped to form the commutator segments. Figure 17 shows how this is done.
Bend the wires as shown so that they will fit closely to the paper core. Bind them tightly into position with some silk thread. Use care so that the two wires do not touch each other. Cut the free ends of the wire off close to the core.
When finished, the relative positions of the armature and the commutator should be as shown in Figure 17.
Figure 14 shows how the motor is assembled. The windings are not shown for the sake of clearness. The armature should be exactly in the center of the field. The bearing holes should be in the correct position and should permit the armature to revolve freely.
The armature should not scrape against the field at any point, but should clear it by about one-sixteenth of an inch.
The brushes are made by flattening a piece of wire by a few light hammer blows.
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