A BOY AND A MOTOR

By Raymond F. Yates

A BOY AND A MOTOR

Harper Books by the Same AuthorTHE BOY’S BOOK OF COMMUNICATIONS

THE BOY’S BOOK OF MAGNETISMA BOY AND A BATTERYA BOY AND A MOTOR

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A BOY AND A MOTOR

A BOY AND A MOTOR. Copyright, 1944, by Raymond F Yates. Printed in the United States of America. All rights in this book

are reserved. It may not be used for dramatic, motion- or talking-picture purposes without written authorization from the holder of

these rights. Nor may the book or part thereof be reproduced in any manner whatsoever without permission in writing except in the case

of brief quotations embodied in critical articles and reviews. For information address: Harper Brothers,

East 33rd Street, New York, N. 1.

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ToSUZANNE STAHLER

good little friend, good little neighbor

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CONTENTS

Chapter 1 THE EARLY MOTOR BUILDERS..................................11

Chapter 2 ELECTRICITY IS LIKE THIS—......................................17

Chapter 3 HOW MOTORS WORK....................................................26

Chapter 4 THE “SIMPLE SIMON” MOTOR....................................35

Chapter 5 THE “WHIRLING CORK” MOTOR................................40

Chapter 6 MAKING “LITTLE SPEEDY”.........................................45

Chapter 7 MAKING THE “ROOFING NAIL MOTOR”..................52

Chapter 8 LEARNING TO “DRIVE” ELECTRIC HORSES............56

Chapter 9 A REVERSER FOR “LITTLE SPEEDY”.........................62

Chapter 10 MOTORS IN THE WORKADAY WORLD...................66

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ILLUSTRATIONS

Fig. 1. Faraday’s first electric generator or dynamo was constructed in the manner shown. When supplied with current, the dynamo became a motor.......................17

Fig. 2. An electric current is generated when a coil is moved near a permanent magnet or in any magnetic field. This is the principle of the electric generator or dynamo...................................................................................................................19

Fig. 3. The shape of the magnetic field of a bar or a horseshoe magnet may he traced by the use of fine iron filings placed over cardboard..................................20

Fig. 4. What is known as the “motor effect” is demonstrated when a magnetic compass is placed near a wire carrying an electric current. Either the North or South pole of the compass will turn toward the wire. This will depend upon the direction of the current in the wire.........................................................................22

Fig. 5. This experiment, performed with an ordinary Boy Scout compass, will show that the reversal of current in a circuit will repel one end of the compass needle and attract the opposite end........................................................................23

Fig. 6. Fine iron filings sprinkled around a wire carrying a heavy electric current will outline the so-called “magnetic lines of force”...............................................24

Fig. 7. A long coil of wire with current traveling through it. produces a magnetic field similar to that produced by a bar magnet......................................................25

Fig. 8. A loop of wire free to move will behave as a magnet when current passes through it................................................................................................................27

Fig. 9. A wire carrying an electric current behaves like a magnet. If it is free to move, it will be attracted or repelled (depending upon the direction of the current) by another magnet. This is called the “motor effect”............................................28

Fig. 10. Coils of wire also behave as magnets when current passes through them. They will be repelled or attracted by permanent magnets.....................................29

Fig. 11. The arrangement of the elements of a simple electric motor with what is known as a “permanent magnetic field”................................................................30

Fig. 12. The arrangement of parts and electrical connections for a simple motor with a permanent magnet field...............................................................................31

Fig. 13. The electrical connections of a “series wound” motor. Here part of the current used to propel the motor is used in creating a magnetic field...................33

Fig. 14. The Simple Simon motor; great for high speed but not much for power.36

Fig. 15. The construction details for the Simple Simon motor..............................37

Fig. 16. The extreme simplicity of the “whirling cork” motor is shown here.......40

Fig. 17. The complete plan for the construction of the “whirling cork” motor.....42

Fig. 18. The “cork” motor is tested by its young builder.......................................44

Fig. 19. “Little Speedy”—the most powerful of the group of motors described...46

Fig. 20. The construction plan for “Little Speedy”................................................49

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Fig. 21. A young engineer gives” Little Speedy” a trial run..................................50

Fig. 22. The construction plan for the motor “roofing nail” motor.......................53

Fig. 23. The “roofing nail” motor complete and ready for business......................54

Fig. 24. How the electric switch and rheostat are made........................................56

Fig. 25. The electric switch, the “key” that “opens” and “closes” the electric circuits....................................................................................................................57

Fig. 26. The electric current regulator or rheostat.................................................59

Fig. 27. The plan and assembly of the water rheostat............................................60

Fig. 28. How electric motors are controlled with a rheostat and a switch.............61

Fig. 29. The construction plans for the current reverser........................................63

Fig. 30. The reversing switch for “Little Speedy”.................................................64

Fig. 31. How the current reverser is connected to the motor and battery..............65

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Chapter 1 THE EARLY MOTOR BUILDERS

In the year 1820, electricity was an infant science. Michael Faraday, that great English Prince of Experimenters, as he was called, was hard at work uncovering the laws of a giant that had been slumbering since the world began. Our own Professor Joseph Henry, not far behind Faraday, was also hard at work in his laboratory at the Albany Academy. And he, too, did much to shoe the billions of “electrical horses” that were later set free to do the work of the world.

This was the birth period of electric power. Nature was slowly yielding a great secret. That electricity and magnetism were related was slowly and painstakingly being uncovered. Wherever electricity was found moving in the forming of electric current, there, too, was magnetism and, curiously enough, when the mysterious sister force of magnetism was made to move, electricity was found present. Men of science began to dream great dreams.

In the late 1820’S, Professor Henry, then one of the great authorities of the new science of electromagnetism, constructed the world’s first large electromagnet. It took the form of an iron core around which many layers of insulated wire were wound. When electric current from a large battery of cells flowed through the wire, a powerful magnetic field was generated and this magnetic field had the power of attraction when iron was brought near it. Professor Henry installed his magnet at the factory of the Pen- field Iron Works in Vermont. There it was used to sift iron ore in the process of separation before smelting. So far as history records, this was the first time electromagnetism was used commercially.

At that time Thomas Davenport, one of our unsung heroes in the great story of electricity, was an obscure blacksmith in the small village of Branden, Vermont. Davenport had heard of Professor Henry’s wonderful electromagnet and he visited the plant of the Penfield Iron Works to see it in operation. Returning to his forge he, too, began to dream great dreams. Surely, he thought, there must be some way in which this pulling power of the electromagnet could be harnessed to produce motion. As the sparks showered from his anvil, he thought of an electric engine having a rotating member carrying a series of electromagnets and so arranged that each electromagnet would be pulled by a stationary electromagnet. Gradually the, idea

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took form until Davenport was so sure of success that he set about constructing the device of his dreams.

In those days, one could not go to the electric shop around the corner to buy wire or accessories and Thomas Davenport was a poor, hard-working man with barely enough income to keep him and 1iis young wife. Copper wire was a rarity and copper with insulated covering was not to be had. Less determined men might have been discouraged but not Davenport.

How much sacrifice he made to purchase his raw wire, the world will never know, but the story of the sacrifice his pretty young wife involuntarily made has been told. After her marriage, she had carefully laid away her silk bridal gown. Davenport found it and, quite unknown to her, took it to his workshop and painstakingly cut it to shreds. Each strip of the silk was wound around his precious copper wire so that the wire could be wound into coils for the magnets of the motor of his dreams.

His job completed, poor Thomas Davenport finally screwed up enough courage to tell his wife of his misdoing. She sat and listened quietly, the tears streaming down her cheeks but she was a brave soul and thereafter the Davenports were of one mind in the completion of a project that finally became the first faltering step forward in the conquest of electric power.

As the model electric motor took form, the Davenports anxiously awaited the day when power from a battery might send it whirling away to its place in history. The little family sacrificed everything but food and the barest necessities of life to hasten that day. Finally, the first motor stood complete on the bench and the Davenports applied the electric current. After a few adjustments, the crude armature of the motor turned and a tremendous chapter in the history of power was opened.

To perfect and exploit his invention, Davenport formed a stock company which he called the Electro-Magnetic Association. We can well imagine the courage of these early stockholders in the electric power industry. They were heroes, every one of them placing their hard earned cash in a venture that, to the common people of that day, must have amounted to an association of dreamers and fools.

It must be confessed that Davenport, hero that he was, had been supplied with the essentials of his motor by other master minds, principally the great Faraday and Joseph Henry, Professor of Natural

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Science at the Albany Academy. Although not so well known as our moderns like Steinmetz, Tesla or Westinghouse, Joseph Henry was an intellectual giant who marked his century (1797-1878) as few others had marked it. Indeed the electric motor was developed like many other great inventions; it was fashioned out of elements supplied by a number of independent workers. The telephone, for instance, would have been impossible save for the work of Volta, Galvani, Faraday and many others, most of them dead and gone, before the fabricator, Alexander Graham Bell, appeared on the scene.

Michael Faraday, the man who, more than any other, paved the approach to Davenport’s motor, was born in London, England, in 1791. At the age of fourteen he was apprenticed to a bookbinder, one Ridban, in Blandford Street, who turned out to be a disagreeable tyrant. Young Faraday’s principal compensation was that of being privileged to read books on science before they reached publication. It was not long before his eager and insatiable mind had grasped the principles of both of the then-infant sciences, electricity and chemistry.

Many shining hours in his otherwise drab existence were also supplied by the lectures of Sir Humphry Davy at the Royal Institution. Faraday’s hungry mind consumed every scrap of Davy’s offerings. Not only that but the meticulous Faraday kept elaborate notes on Davy’s lectures and, when the series was completed, the young man bound his papers and submitted them to Sir Humphry with the request for employment at the Royal Institute in the place of one William Payne who had been engaged as handy man about the laboratory; a sort of janitor who washed bottles, swept floors and made himself generally useful.

Sir Humphry was impressed with Faraday’s notes and his first interview with the young man, who was then twenty-two years of age, resulted in his recommendation to the managers of the Institute that he be employed. Faraday was accepted and the world lost an indifferent bookbinder and gained a Prince of Experimenters whose contributions to electrical science founded electricity in the workaday world. It was Faraday more than any other man who bridged the gap between electricity as a curious laboratory phenomenon and electricity as an agent of industry.

If we wish to confine our definition of an electric motor to the creation of mechanical motion through electrical means, Michael

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Faraday invented the first motor during 1821, sixteen years before Davenport’s contribution. His motor, which we shall examine later, was not, however, able to deliver power whereas Davenport’s was able to propel small machines. In Faraday’s case, he merely caused two small wires carrying electric current to revolve about a magnet under the impulse of electromagnetic forces. This now-famous experiment bore fruit for the first time on Christmas Day, 1821, shortly after his marriage. The young couple lived in a few rooms above the headquarters and laboratory of the Royal Institute and Faraday called up to his young wife to “come see them dance,” meaning the moving wires. Here was the birth of an idea that was to be of tremendous significance to the world although at the time it was appreciated by only a few men with a knowledge of the bare essentials of electrical science. Today, we have electric motors delivering power that could be matched only by 10,000 straining horses.

Faraday’s creation of motion by the interplay of electromagnetic forces was soon followed by another classical experiment conducted by Peter Barlow of Woolwich, England. It was in 1824 that Barlow came forth with a metal wheel that was made to revolve slowly in a magnetic field supplied by an ordinary horseshoe magnet. This amounted to the next step in the development of the electric motor. Although the little disc could barely move itself, it did revolve and it did further demonstrate that properly arranged electromagnetic devices were capable of producing continuous motion.

Thomas Davenport knew little or nothing about Faraday or Barlow. He was not a learned man in the sciences but he was imaginative, patient, and persistent which are, after all, the principal qualifications of genius. Davenport drew his inspiration from Professor Joseph Henry whose contributions to electrical science were of the first order of importance and who, quite unwittingly, duplicated many of Faraday’s researches with identical results. For one thing, he improved electromagnets which were made by winding wire around pieces of iron. When electric current was passed through the wire from batteries, the iron would become magnetized and remain so until the electric current was withdrawn.

The power of such electromagnets was limited for two reasons. First, all electric current of that day was generated by batteries. Indeed it was part of poor Faraday’s early morning chores at the laboratories

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of the Royal Institute to revive or renew his batteries so that they might last out the day. The power of such devices was also limited because wire had no insulation and only one layer of wire could be wound around a piece of iron. Professor Joseph Henry saw that it might be possible to insulate wire and thereby separate the turns and layers so that electromagnetism could be made more powerful and more concentrated. He and his associates laboriously wound hundreds of feet of wire with silk cloth and large electromagnets so prepared were finally able to lift as much as 3000 pounds of iron although supplied with current by a series of faltering electric cells. Little did Professor Henry realize that he was shaping the doom of a young bride’s wedding gown!

At the time Thomas Davenport was hard at work on his motors, another patient fellow in Russia, Moritz Hermann Jacobi, was also experimenting and his design was quite similar to Davenport’s. His final motor was very large and required a large battery of electric cells for its current. Jacobi was so thrilled with the results that he built a small boat and propelled it with his motor on the Neva River.

After Davenport and Jacobi came a long list of motor builders, designers, improvers, and inventors. Indeed the work of perfecting the electric motor still goes on, as the weekly issues of our Patent Office Gazette show. Immediately following the two pioneers about whom we have been reading, Fromant, Farmer and Pacinotti each made a contribution toward improvement but each was finally thwarted because of the lack of adequate sources of electric current. The chemical cells used in the batteries were expensive and troublesome and failed quickly when called upon to supply a large volume of current. A new and better generator of electric power was needed. Men had motors but little with which to drive them.

Again the brilliant mind of Michael Faraday came to the aid of the infant giant, electricity. It was Faraday’s researches that paved the way to the dynamo and it was the dynamo that made the use of large, powerful electric motors practical. The dynamoelectric machine was very similar to a motor but, in place of using electricity, it generated electricity when it was driven by a steam engine or a water wheel. In each case, mechanical energy was converted to electrical energy and converted back to mechanical energy through the agency of the electric motor. Large dynamos generated large amounts of current but it was not in the nature of things that any generator of electricity

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should deliver in electric current more than the equivalent of the mechanical power used to drive it. Inasmuch as such machines were never 100 per cent efficient (no machine is, as a matter of fact) they would deliver less power than was supplied to them.

So much for the brief history of the electric motor up to the invention of the dynamo. Fortunately for the young reader of this book, many of the experiments conducted by Faraday and the early electrical experimenters may be duplicated with simple and in-expensive homemade equipment. The duplication of these experiments will amount to exciting adventures in electrical science and they will teach the student many of the basic facts of electrical engines. Thereafter, we may approach the construction of toy motors with confidence born of knowledge.

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Chapter 2 ELECTRICITY IS LIKE THIS—Although the date of October 28, 1831, has not been set down

by our historians, it turned out to be one of the most important days in the history of mankind. Michael Faraday made it so when he mounted a small metal disc between the poles of a magnet. Two metal brushes or contactors were arranged, one on the shaft and one on the edge of the disc, so that electrical connection could be maintained while the disc revolved. Each contactor or brush was connected to a sensitive galvanometer or current measuring device. The simple arrangement is shown in Fig 1.

Fig. 1. Faraday’s first electric generator or dynamo was constructed in the manner shown. When supplied with current, the dynamo became a

motor

When Faraday turned the metal disc with the small crank, the galvanometer or electric meter showed that an electric current was generated and flowed in the simple circuit. When the disc was stopped, no current flowed and, when it slowed down, less current flowed. Here mechanical energy was being directly converted into electrical energy. At last a way had been found to produce electric current without the aid of the chemical or voltaic cell. The bands should have played and a holiday should have been declared but Faraday’s contribution caused not a ripple except among a small group of experimenters associated with electrical research. Even Faraday himself went about the Royal Institute laboratories much as usual, little dreaming of the tremendous importance of his invention.

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Having accomplished the feat, he set about analyzing it. Into his meticulous notebooks went the basic principles of dynamoelectric machinery and, although over a hundred years have passed by, these principles, as set down by him, still stand. Time has treated them well.

No young student of electricity or builder of motors should pass by the story of the dynamo. Here we find not only a large part of the story of electricity itself but we also discover that there is little difference between dynamos and motors. When motors of certain types are driven either by other motors, water wheels or engines, they become dynamos; in place of consuming current, they generate it.

In a sense, a dynamo is like a pump in a water system. The larger it is, the greater the amount of electricity it will generate and the greater the amount of power that must be used to turn it. Some of our dynamos or generators in use today require as much as 70,000 horsepower to drive them. This would amount to a single file of horses extending for a distance of ii o miles or from New York to Philadelphia with 20 miles of horses left over.

The “faster” the dynamos “pump” electricity, the greater will be the voltage generated, and we discover that electric voltage is similar to that which we call pressure in a water system. Here we find that, as in the case of the water wheel, there can be very high electric pressures or voltages without a great deal of power. For instance, water may issue from a nozzle at a pressure of 1000 pounds per square inch (which is a very high pressure) and yet, if the stream issuing from the nozzle were directed against a giant water wheel, it would not budge it. The giant water wheel would need water volume as well as pressure. So it is with electricity. A million volts of electricity is no index of power. A million volts might not have enough energy to move a toy electric motor. For real power electricity, like water, must have “volume” and this “volume” is called current or amperage. The ampere means work and the volt refers to that part of electric current that supplies the pressure or the force that pushes the current through the wires of an electric circuit.

A proper understanding of the dynamo or motor requires an understanding of the first principles of electricity and magnetism, two very closely related sciences. Indeed they are so closely related that scientists have difficulty in discovering where electricity begins and magnetism leaves off. It is much like the two sides of a single coin. Magnetism is always generated when electricity moves through a wire

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and electricity is always generated in wires and conductors when either magnets or the wires or conductors are moved when they are close to each other. Here again the work of the genius, Faraday, established this law by the use of the simple equipment shown in Fig.2. He employed a simple hollow coil of wire (now called a solenoid) connected to a sensitive current detector or galvanometer. When Faraday plunged an ordinary steel magnet into the coil, the needle of the galvanometer moved, proving the presence of electric current. When the magnet remained motionless, however, no electric current was generated. The only way in which electricity could be produced with a stationary magnet was to move the coil instead of the magnet. Of course, moving either the coil or the magnet represented work and it was early discovered that with no work, there was no electric energy. This was very much in keeping with the general laws of nature that prove that we cannot get something for nothing. It would be very fine indeed if we could simply leave a magnet inside a coil of wire and generate all of the electricity that we needed. But the matter is not nearly so simple as that.

Fig. 2. An electric current is generated when a coil is moved near a permanent magnet or in any magnetic field. This is the principle of the

electric generator or dynamo

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Pushing our study of first principles back further, we arrive at the very beginning; the ordinary steel magnet. Iron can be magnetized and will conduct magnetism but, unlike steel and for some reason not yet thoroughly understood, it will not hold its magnetism. Drawn away from the source, it quickly reverts to its non-magnetic state. Steel, on the other hand, tenaciously holds on to its magnetism; not all of it but most of it.

Magnetism, like electricity, is invisible and it was Faraday who first visualized magnetism from a magnet as being composed of “lines of force”; something like invisible tentacles that reached out to grip and hold or pull magnet-ward metals like steel or iron.

If some thought is given to this matter we come to see that iron powder or finely divided iron-like filings might act in the manner of independent small magnets in the presence of magnetism and that they might set themselves up to follow the mysterious “lines of force.” This is very true. To discover it for ourselves, a piece of light cardboard is placed over the ends (or poles) of a magnet as shown at A in Fig. 3. The finely divided iron particles behave as tiny soldiers toeing the lines of force even when the lines bend and it is discovered that they do bend in a manner depending upon the shape of the magnet. At B (Fig. ) the cardboard and filings are placed over what is known as a bar magnet. Here it is seen that at the midpoint of the bar, magnetism reaches a zero point. The lines of force are most intense near the ends of the magnet and they curve out from this point becoming weaker and weaker as the distance increases.

Fig. 3. The shape of the magnetic field of a bar or a horseshoe magnet may he traced by the use of fine iron filings placed over cardboard

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All magnets have what are known as poles. One end is called the North (N) pole and the other or opposite end is called the South (S) pole. The behavior of one pole toward the other is most interesting. It is found that when an N pole is brought near an S pole, attraction takes place. Not so when S and S or N and N poles are brought together. Here a rather violent form of repulsion or “pushing away” is noticed. One of the basic laws of magnetism and electricity is derived from this behavior and it states in very simple terms that “like or similar poles repel each other and dislike poles attract each other.”

One of the most sensational discoveries in the history of science showed the mysterious connection between electricity and magnetism. Prior to 1819, the men who had experimented with electricity were strongly suspicious of some relationship between it and magnetism but no one, not even the all-seeing Faraday, was able to place a finger on it and say, “There it is.”

The discovery was left for a young Danish professor of Physics at the University of Copenhagen, Hans Christian Oersted. Up to Professor Oersted’s time, it was not known that a magnetic field surrounded a wire carrying an electric current. Surmising that such might be the case, Oersted thought that if this was so, an ordinary compass should indicate the fact. As a result of his suspicions, he set up the simple experiment shown in Fig. 4. The compass needle was in a normal position and its South pole was pointing at the earth’s North pole. Unfortunately, nothing happened when Oersted sent a current through the wire. Still mystified, he abandoned the experiment. Some time later, during the year 1819, Oersted was using an electric circuit and a compass sat close by on his laboratory bench. This time, and quite by accident, he noticed that the compass needle moved violently when current passed through the electric circuit and that the needle pointed toward the wire carrying the current. When the current was reversed in the circuit, the needle would promptly reverse itself; that is, the opposite end would swing around. Oersted’s first experiment failed to yield results because the needle of the compass was already pointed at the wire and Oersted failed to reverse the current in the circuit.

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Fig. 4. What is known as the “motor effect” is demonstrated when a magnetic compass is placed near a wire carrying an electric current. Either the North or South pole of the compass will turn toward the wire. This will

depend upon the direction of the current in the wire

When the knowledge of Oersted’s discovery spread and it was actually found that electricity was closely related to magnetism, Faraday’s eager mind was given a great deal of fuel and his greatest discoveries promptly followed. So many new experiments were suggested that it took him many years to perform all of them.

Fortunately for the student, many of these early masterpieces of research may be duplicated by simple equipment and very little preparation. A single dry cell, even of the flashlight type, and a ten-cent store Boy Scout compass may be used to duplicate Oersted’s great experiment. The arrangement is shown in Fig. 5. The reversal of the current is brought about by reversing the position of the wire where it is connected to the dry cell. The dry cell should not be left connected in this manner for more than a few seconds at a time because this amounts to a direct short circuit which will soon damage the cell.

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Fig. 5. This experiment, performed with an ordinary Boy Scout compass, will show that the reversal of current in a circuit will repel one end

of the compass needle and attract the opposite end

Another simple experiment may be conducted to show that the magnetic field surrounding a wire carrying an electric current has a definite pattern just as in the case of the magnetic field of force issuing from the poles of a magnet. The demonstration is made by pushing a wire through a piece of cardboard, as shown in Fig. 6. Only the barest sprinkling of iron filings is made to increase their sensitivity to the magnetic effects of the current that is sent through the wire.

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Fig. 6. Fine iron filings sprinkled around a wire carrying a heavy electric current will outline the so-called “magnetic lines of force”

Although this is a simple experiment, one with a flare for research would notice several things. First, it would be seen that the magnetic lines of force were perfectly round. Secondly, it would be noted that they are arranged concentrically (one within the other) and that they are closer together near the wire. As they spread out from the wire they become more widely separated, indicating growing weakness. Further experimentation would show us that the stronger the current passing through the wire, the stronger the magnetic field generated. There is a very direct relation between the two.

It was to be expected that sooner or later, the early experimenters, having found that magnetism was generated by the passage of electricity through wires, would seek to find some way in which the wire could be concentrated or bunched so as to concentrate the magnetic effects. Wire was therefore insulated and then formed into coils. Current was then sent through the coils and the shapes of the magnetic fields depended upon the shape of the coils. In Fig. 7 we see the magnetic pattern developed by an ordinary coil. Such coils behave precisely like ordinary magnets. They have North and South poles. These may be reversed by reversing the current.

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Fig. 7. A long coil of wire with current traveling through it. produces a magnetic field similar to that produced by a bar magnet

Among the questions that the inquiring young mind might ask would be, “If a coil of wire carrying an electric current behaves like a magnet, could such a coil be used in place of a compass? In short, would its N pole be attracted by the S pole of the earth and vice versa?” The answer to this is definitely yes, the problem being a simple mechanical one. It might be diflju1t to make a light weight coil and to suspend it in such a way as to make it sensitive enough and at the same time carry current to it.

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Chapter 3 HOW MOTORS WORK

Our last chapter explained the relationship between electricity and magnetism. We are now prepared to tackle the subject of the motor by itself and to discover what makes it go.

By way of a brief review, it will be recalled that like magnetic poles, whether on magnets or coils, repel each other and that dislike poles (as N and S) attract each other. Therein lies a great deal of the secret of electric locomotion. Were it not for these simple and easily understood facts, there would be no electric motor. Of course, the matter of attraction and repulsion can also be expressed as “pushing” and “pulling.” In the steam engine, the pressure of the steam pushes the pistons forward and the momentum of the flywheel pulls it back again. We have some form of “push” in all of our engines.

The last chapter also brought out the fact that the interaction of a magnetic field generated by a so- called permanent steel magnet and one generated by a coil of wire was the same as the interaction of magnetism generated either by two magnets or two coils. This is just like saying that there is only one kind of magnetism regardless of its source.

In Fig. 8 and the photograph an experiment is illustrated which has been called the “motor effect.” Here a piece of wire forming part of an electric circuit has been arranged on two hinges so that it may be moved up or down. As current from a battery moves through the wire, a steel magnet brought near the hinged wire w1lFeither attract or repel it depending upon (1) the direction of the electric current in the wire and (2) which one of the two poles of the magnet are brought near the wire.

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Fig. 8. A loop of wire free to move will behave as a magnet when current passes through it

If a permanent magnet will attract or repel a single wire carrying an electric current, what might happen if a very large and powerful permanent magnet was brought near a large coil carrying a heavy current? The answer is simple and is just what might be expected; there would be much more powerful attraction and repulsion or pushing and pulling. It has long since been known that the degree of pushing and pulling is limited by the power of the magnetic fields in the motor coils. If the coils are large and are supplied with very heavy electric currents, a large number of horsepower will be generated by the motor. The power produced may be approximately calculated by the application of fifth grade arithmetic if the amount of electricity in volts and amperes consumed by the motor is known. If the motor operates at 110 volts and consumes 10 amperes, we simply multiply 110 by 10 which equals 1100. Multiplying volts by amperes supplies the unit of electric power, the watt, named in honor of James Watt, the early designer of steam engines. We have, then, 1100 watts of power. It so happens that there are 746 watts in a horsepower and if 1100 is divided by 746 it is found that 1100 watts is approximately the equivalent of one and one-half horsepower.

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Fig. 9. A wire carrying an electric current behaves like a magnet. If it is free to move, it will be attracted or repelled (depending upon the direction

of the current) by another magnet. This is called the “motor effect”

The thoughtful young reader will perhaps begin to surmise how motors operate. He will visualize some sort of a rotating member with coils and a stationary coil or coils supplying the magnetism that reacts with the magnetism generated by the coils carried on the rotating member. By the aid of some sort of shifting electrical contacts arranged between the power source, which may be a battery, and the revolving member, he can see how it would be possible to keep the moving coils “at odds” with the stationary ones so that a quick series of “pushes” and “pulls” would keep the revolving member in motion. The revolving part of the motor, it seems, is called upon to catch its electricity “on the fly” as it were. However, this should not be difficult because we all know that electricity is far quicker than “scat.” It is capable of reaching a speed of 10,000 miles a second through wire. Things would have to move pretty fast to keep up with that.

In the drawing, Fig. 10, another experiment is shown to demonstrate what engineers call the “motor effect.” Here a hollow electric coil (always called a solenoid) is suspended by electric wires in such a way that, even while it moves, it can receive electricity. Thus when a direct current is sent through this coil, the coil will perform like a magnet. One end will be North and the opposite end will be South. Reversing the current will reverse the magnetic poles.

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Now if a strong permanent magnet, or another coil excited with direct current, is brought near the suspended coil, one of two things will happen. Either the suspended coil will be pulled toward the magnet or the coil, acting as a magnet on it, or it will be repelled or pushed away. This will depend upon which of the two poles of the approaching magnet or coil is pointed at the suspended magnet.

Fig. 10. Coils of wire also behave as magnets when current passes through them. They will be repelled or attracted by permanent magnets

Really this device amounts to a very simple motor. If the elements were arranged properly, it would be possible to keep the suspended coil in motion. If the magnet (or coil) held in the hand were reversed at the proper speed, it would always be in a position to pull or attract one end of the revolving coil. We can also understand that it might be possible to use two reversed magnets to act on the revolving coil in such a manner that one would be pushing while the other was pulling.

The drawing, Fig. 11, shows the construction of a small motor used to demonstrate the principle of electric locomotion. Study of the

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drawing reveals a revolving coil mounted on a shaft and a permanent magnet so arranged that the coil revolves close to it. It will also be noticed that one end of the revolving coil is connected to the shaft upon which it revolves, and that the other end of the wire comprising the coil is connected to a pin. The pin is so positioned in relation to the moving coil that every time the coil reaches a certain definite position in relation to the magnet, the pin contacts a tiny brass strip connected to a battery. If the electric circuit is traced through, it will be found that this completes the electric circuit and for an instant (just the proper instant indeed) electric current flows through the coil. Thus is the coil repeatedly attracted to the magnet as it revolves. It is in this way that the tiny coil receives what we might call an electromagnetic”kick” every time it reaches a certain position. Of course, when the simple motor is in operation, the action happens so rapidly that the eye cannot follow it.

Fig. 11. The arrangement of the elements of a simple electric motor with what is known as a “permanent magnetic field”

In Fig. 12 the simple electrical connections of an improved form of elementary electric motor are given. Here it is found that two. Small and flexible strips of sheet copper or brass are used to keep current flowing through the coil as it revolves. This current is permitted to flow at just the proper instant so that the proper sequence of repulsion (push) and attraction (pull) will take place between the magnetic field of the permanent magnet and the magnetic field of the revolving coil. It is in this fashion that electric energy is changed directly into mechanical energy. The more electric energy fed to the motor, the greater the power of the motor.

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Fig. 12. The arrangement of parts and electrical connections for a simple motor with a permanent magnet field

As young electricians, we must understand that the magnetism generated by the magnet is also important. If this is weak, the motor will be weak no matter what its size or how much electricity we feed to it. The amount of electricity consumed by a motor will not only depend upon the size of the motor and the amount of wire in its revolving coil but also upon the work required of the motor or, as the engineers say, its load. If the motor has no load but is running light, then very little electricity will be used. As soon as a load is placed on the motor, the electric power consumed will rapidly increase and if the load becomes greater than the electric power present to run the motor, the motor will stall. On the other hand, if a motor operates with an overload where the source of electric power is sufficient, the machine will become heated’ and finally burn out. It must also be clear to the young reader that we could not expect to have a very powerful motor with one loop of wire as the moving part and a small permanent magnet for the magnetic field. As we move along, the methods used in building large, powerful motors will be discovered.

Coming back to our analysis of the motor (see Fig. 12) it is noted that the loop of wire comprising the moving part is shown in a horizontal position. The direction taken by the electric current

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supplied by the battery is indicated by the arrows. At this particular instant, with the moving loop of wire in this position, the North pole of the magnet will exert an upward force on the A section of the loop while the South pole of the magnet will exert a downward force on the B side of the loop.

Now let us imagine that loop of wire in a vertical position. Here it is practically free either of attraction or of repulsion but it must be remembered that all moving things have something called momentum; they tend to move along after the power that caused them to move is withdrawn. This is the reason why automobiles coast after the clutch has been pushed in. In the case of the tiny loop of wire, it also “coasts” beyond the dead point-or vertical position. However, when a point much beyond this is reached, it will be noted that the sliding contacts bearing on the rotating contact members (commutator) reverse the electric current from the battery and when this happens the electromagnetic force continues the rotation of the wire loop.

Now it so happens that permanent magnets produce limited magnetism. A magnet of a given size becomes, as the engineers say, “saturated,” and no matter what is done, it will have reached its limit insofar as the strength of its magnetic field is concerned. The use of such magnets would place a distinct limit on the power of motors. How can this limitation be overcome?

An earlier chapter of this book referred to the magnetic fields that surrounded wires carrying electric current. Every inch of even the longest wires carrying electric current are encased in this invisible and mysterious “pulling” and “pushing” power. Clever young engineers will quickly see that if this wire, in place of being stretched out over a great distance, is rolled up into a tight little coil, in a sense the magnetism will be ”rolled up” also and the magnetism will thereafter be highly concentrated when an electric current is passed through the coil. Such a coil is called an electromagnet and the use of the electromagnet permits us to set up extremely powerful magnetic fields. When such coils are properly designed and heavy currents are sent through them, extremely powerful attraction can be generated.

Owing to the limitations of permanent magnets, it would seem advisable to re-design the simple motor shown in Fig. 12, substituting an electromagnet for the permanent magnet. This turns out to be an exceptionally clever move which, with other changes, will provide a great deal more power. Of course, greater power will never be

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realized so long as the moving coil is comprised of a single wire. The power delivered by any motor depends upon the intensity of the interacting magnetic fields and if one is strong and the other weak, a weak motor will result. In order that both the magnetic fields of our re-designed motor shall be strong, it will be necessary to add considerable wire to the revolving loop. In place of a single loop, perhaps thirty or forty loops may be placed in position but the size and length of this wire must depend on the strength of the magnetic field generated by the stationary coil which is wound upon a soft iron piece as illustrated in Fig. 13, showing the redesigned motor.

Fig. 13. The electrical connections of a “series wound” motor. Here part of the current used to propel the motor is used in creating a magnetic

field

Somewhere it was said that magnetism passes through iron with less effort than it passes through air. Engineers who design motors are most interested in permitting the magnetism of a motor to pass between its poles and through its moving coils with as much ease and freedom as possible. Therefore, they always wind these revolving coils on soft iron drums.

Now that a new motor has been assembled, it might be well if we stopped for a moment to learn the names of its parts. The wire wound around the soft iron body of the motor is called the field coil. This, it will be noted, is connected in such a way that the electric current from the battery passes through it on its way to the revolving

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coil. The field coil is said to be in series with the revolving coil and this is called a series wound motor.

The revolving coil (or coils) of a motor of this and similar types is called the armature. The copper contactors mounted on the motor shaft are called segments and they comprise what is known as the corn- imitator. Electrical connection with the revolving segments of the commutator, which really amounts to a revolving switch distributing current to the revolving coil or coils at the proper instants, is established by means of contactors called brushes which, in the case of small toy motors, may amount only to light springy copper. Larger and more powerful motors have brushes made of soft carbon which is a good conductor of electricity. Brushes, no matter what they are made of, always press gently against the segments of the commutator.

The electric motors used in the workaday world differ somewhat in construction depending upon the current (A.C. or D.C.) that is used and the services for which they are intended.

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Chapter 4 THE “SIMPLE SIMON” MOTOR

So far our lessons in motor electricity or, as the engineers call it, electrodynamics, have been confined to the classical principles. With the very simple motor at hand, a new idea takes form. Here is a motor that does not conform to standard practice. Yet it is practical and any enterprising young electrician may have a great deal of fun with it.

The basis of its operation is delightfully simple to understand. Even a quick examination of Fig. 14 will help the young reader to grasp the idea back of the machine. Here we find a soft iron bar with a small shaft mounted in its center. The bar is free to revolve before the simple electromagnet which receives its current from a near-by dry cell. It will be clear that when current flows through the electromagnet, the electromagnet will attract the end of the soft iron bar nearest to it and that that end of the bar will move toward it inasmuch as the whole bar can swing around on the shaft. Of course, if the current remained in the electromagnet, it would continue to attract the end of the bar and the whole bar would then remain stationary after it reached the point closest to the end of the electromagnet. We can see, however, that continuous motion might result if some sort of mechanism was fixed that would automatically turn the current on and off when the revolving bar reached the position shown in the drawing. Fortunately, this mechanism may be easily devised. All that is needed is a small spring that will contact the ends of the revolving soft iron bar at the proper instant so that electric current will flow through the electromagnet at the proper instant. It must also be turned off at the proper instant.

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Fig. 14. The Simple Simon motor; great for high speed but not much for power

The little motor about to be made has a number of things to recommend it. It will last for years, it is simple to fashion, and it develops a very high speed. Only a modest set of tools is required and any boy who is at all clever with his hands should be able to complete the job of construction in a half day.

Construction is started with a 1/4 -inch (diameter) iron carriage bolt 5 inches long. This is available at almost any hardware store for about three cents. This should be cleaned with emery cloth and bent in a vise to the shape indicated in Fig.15. This shaping will have to be accomplished with a rather heavy hammer and the job should be done with as much accuracy as possible. The builder will note that the threaded end of the bolt is carefully preserved and that the head of the bolt is cut off with a hacksaw. Later the threaded end turns out to be very useful in fastening the electromagnet to the wooden baseboard.

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A BOY AND A MOTOR

Fig. 15. The construction details for the Simple Simon motor

The electromagnet is wound on the iron bolt but, before this can be done, some sort of preparation must be made because good electricians never wind wire directly over metal even though the wire is insulated. The surface of the bolt at the point where the wire is to be placed is first covered with a single layer of ordinary electricians’ friction tape or the sort of adhesive tape found in the medicine cabinet.

Once more the young motor builder will have to impose upon the good nature of the local electrician or radio store proprietor for a bit of wire with which to wind the electromagnet of the motor. This may have either cotton, silk or enamel for insulation. About 40 or 50 feet of No. 22 to 24 will serve nicely and it should be wound into

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A BOY AND A MOTOR

position as tightly as possible. Upon the completion of the winding, one must be careful not to allow the wire to unwind partially by leaving the free end loose. This should be temporarily twisted with the other or starting end, several inches of which should be left protruding for the establishment of electrical connections after assembly has been accomplished.

Perhaps the builder will have to search for the piece of soft iron to use as the revolving member. Care should be taken to see to it that steel is not used in place of soft iron because in that event our otherwise speedy little motor will not function at all. Any sort of scrap iron or wrought iron will do, and here it might be advisable to seek father’s assistance. If he is not able to help, then a machinist or a repair man who works with metals should be able to supply guidance.

This soft iron bar is cut to the size shown. As the drawing instructs, it will be necessary to drill a small hole through the center of the bar for the shaft which may be a small finishing nail with the head cut off. Both ends of the nail are brought to a sharp point by the aid of a fine file. Pivot bearings are used because they offer very little friction and will permit a low- power such as this one to reach a very high speed. The little bearing members are cut from the sheet metal of an ordinary tin can and the dimples or indentations for the pointed shaft are made either with a prick punch or a large darning needle. A sharp blow with a small hammer is all that is needed. Once the assembly has been made, a single drop of very light machine oil on the pivot bearing will still further reduce resistance.

Next, the builder must provide the spring electrical contact. It is the function of this member of the motor parts to contact the whirling bar (really the armature) of the motor so that electricity will flow through the electromagnet at just the proper instant. It is these impulses of magnetism that keep the ends of the bar of soft iron flying electromagnet-ward while the motor is in operation. A piece of thin spring brass will serve nicely for this member but, if this is not available, ordinary “tin” will do. In any event, very careful adjustment is necessary here. Only the slightest contact is necessary at each end of the bar. Too heavy a contact will steal all of the energy generated by the little motor and it will stop. The builder must also realize that this is not a self-starting motor. Each time it is started, the builder must give it a good send-off with his fingers.

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One dry cell is usually sufficient but a battery of two will develop a great deal of motor speed. The little device consumes such a small amount that it will operate for a good many hours on a single cell. If the luxury of a battery of four cells is possible, then one might develop enough power to drive small light toys.

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Chapter 5 THE “WHIRLING CORK” MOTOR

As inexperienced motor makers, we shall have to be satisfied at first with motors that are powerful enough to move themselves only. This means, in short, motors that simply “go” and that do not have the power necessary to drive other mechanisms.

Fortunately for the young motor maker who does not have access to large stores of materials and tools, our “flying cork” model may be assembled with bits and parts found about the house, provided two small toy magnets are at hand. These are used to supply the magnetic field.

Inasmuch as the armature or the revolving part of the motor is the most important member of the assembly, that might well come first on the construction list.

Fig. 16. The extreme simplicity of the “whirling cork” motor is shown here

A cork is among the primary requisites and it must be a very special kind of cork, one without a taper. A diligent search around the house will usually turn up a cork of this sort. If such a thing cannot be found, then a piece of balsa wood may be cut to this size and shape. Such a job calls for some accuracy. The armature body must be perfectly round. Otherwise it will be badly out of balance when it revolves and the speed of the motor will be greatly reduced as a result. Should the unbalance be too great, the motor will fail to operate at all.

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A BOY AND A MOTOR

The next thing on the list of materials is wire and here the builder may have to hie himself to the local radio shop for help. Very fine insulated wire is needed and it should be of No. 28 or 30 gauge. It so happens that every radio shop has plenty of such wire about in old radio sets and in obsolete equipment such as radio and audio-frequency transformers. Seven or eight feet of the wire will be plenty, but the shop proprietor may simply give the applicant one of the devices upon which the wire is wound. Careful removal of the wire will be necessary to prevent it from kinking or to prevent the loss of the insulation or covering.

Before the winding is started, the builder had best find the center of the cork or balsa wood armature form. Perhaps as much as a half hour should be devoted to this task if we are to have a nicely balanced, smoothly running motor. Testing of this kind must be done with the bearings. Therefore the builder should cut them to shape from a tin can and mount them as shown in the drawing, Fig. 17. This done, a pin is driven into the center of each end of the armature form and this is then rested on the bearings and spun with the fingers. If the armature form will spin for some time, good balance has been achieved. If not, there will be a very noticeable wobble and the armature will come to rest in a short time. In this event, the builder withdraws the pins, re-sets them and tries once more to achieve balance. Time spent in this adjustment will be amply repaid.

Balance achieved, two more pins are set in place as indicated in the drawing, Fig. 17. These, too, must be positioned at an equal distance from the, center of the armature so that they will not destroy the balance of the revolving part.

The latter two pins are to serve really as segments of a commutator; indeed they are the commutator.

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A BOY AND A MOTOR

Fig. 17. The complete plan for the construction of the “whirling cork” motor

As will be noticed in the drawing, they are so placed as to make flying contact with two small stationary wires connected to the terminals of the dry cell. Another part of the secret of making this motor operate at high speed lies in arranging these tiny wires in such a way as to make only the gentlest contact with the flying pins as they pass. The pins used must be of the same size.

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The winding of the armature must be done with great care and exactly the same number of turns of wire must be placed on each side. To start the winding, the builder first clears the insulation away from the end of the wire for a distance of exactly one inch. This bare end is then tightly wound around one of the contactor pins previously placed in the end of the armature drum or form. The winding is then begun and continued until twelve turns are put in place on one side of the form. Then a cross-over is made and twelve turns are placed on the opposite side of the form. The builder should try to put the wire in place with even tension in an effort to further preserve the balance of the moving part. Should too much unequal winding tension be used, one side of the armature will have more wire on it than the other and only a slight difference is necessary to destroy any balance previously achieved.

When the armature winding was begun, the builder was asked to peel off just one inch of the insulation so that this inch of bare, clean wire could be wound around one of the contact pins. When the last turn of wire is set in place, this same procedure is followed, again in an effort to preserve the balance of the delicate little armature.

Owing to the high speed developed by a motor of this type, it may be advisable to wind two or three turns of thread around the middle of the armature to prevent the wire from becoming loose and shifting its position. In any event, if the builder has a bit of shellac handy, no harm will be done by covering the whole armature with this preparation. The excellent adhesive properties of this may make it unnecessary to use the thread.

After the small stationary contactor wires have been set up and adjusted so as to cause minimum interference with the movement of the armature, the magnets are put in place on the blocks. Full power and the highest speed will be developed by the motor only if the poles of the magnets are brought as close as possible to the armature. The relationship of the facing poles of the magnets is also of great importance because the motor will refuse to run if these are not correct. Thereafter, if the motor refuses to run after the dry cell is connected to it, one of the magnets is turned upside down, which reverses its poles. If this is the trouble with the motor, the correction will have been made and the motor should start off, Of course, the motor will refuse to start if the two pins on the armature are out of contact with the stationary wires at the moment the current is applied.

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Otherwise, no current from the dry cell will be able to reach the armature coils. Hence, a spin with the fingers will also set the motor off to a sure, quick start.

Fig. 18. The “cork” motor is tested by its young builder

There is little advantage in using more than the power of a single dry cell on this motor. Indeed the use of a battery of two or more dry cells would cause the coils of the motor to heat badly and the cells would be very short-lived as a result of too great a current drain.

Back in the second chapter of our little book, we said something about the power of any motor depending upon the strength of the magnetic field. There is a wonderful opportunity to prove this point with the motor at hand. The small magnets used for the magnetic field need only to be moved further away from the armature. As they are moved back, a point will eventually be reached where the magnetic field in the vicinity of the armature will become so weak as to stop the motor.

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Chapter 6 MAKING “LITTLE SPEEDY”

“Little Speedy,” as the boys who made the original called it, is a remarkable motor. It is capable of a speed of 2,000 revolutions per minute and, like all of our motors, it calls for very simple techniques and materials in its construction. What is more, it will, with reasonable care, serve us faithfully throughout our childhood, always ready and willing to supply power for our toys.

First, we shall need a small horseshoe magnet. The size and actual shape is not important so long as the magnet is powerful. If it is weak, our motor will also be weak. Should the builder be able to purchase one of the newer Alnico magnets, then he will have a far more powerful motor than would otherwise be possible.

Our present motor, although it may not look the part when compared with the large motors of the workaday world, is built along classical lines, the design having been taken from the early motors that appeared during the middle of the last century. When made with reasonable care, it will be found to be powerful enough to drive small toys.

The armature of the motor is a two-pole affair and, as in the case of our “Cork” motors, it revolves before the permanent magnet (North and South poles) because one of its poles is attracting one leg or pole of the revolving armature while the opposite leg or pole is repelling the other. This action is automatically continued because the commutator carried on the armature shaft changes the direction of the current passing through the armature coils at just the proper interval. At all times, one pole of the flying armature is being “pulled” by one of the poles of the magnet (as N+S) while the opposite pole is being “pushed” (as N—N or S—S).

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Fig. 19. “Little Speedy”—the most powerful of the group of motors described

Perhaps the builder will have to do a bit of searching before he comes upon a piece of soft iron of the right size that may be used in the construction of the armature. This cannot be of steel. The steel will become quickly magnetized and thereafter our little motor will be a motor in appearance only. A local blacksmith will be able to help if he has a supply of what is known as scrap iron. A piece about 6 inches long, 1/2 inch wide and 1/8 inch thick will serve the purpose nicely and a bit of annealing will do no harm. To do this, the piece is held in the flame of a gas stove until it becomes red hot. It is then left to cool gradually. Such treatment will still further soften the iron and that is what is needed; the softer the better. This done, the builder will proceed to cut the soft iron piece to the dimensions indicated in the drawing. Only a fine file and a hacksaw will be needed for this work..

Once more, the amateur motor builder is cautioned to seek accuracy at this point. Should one end of the piece of soft iron be filed away more than the other, trouble will result later on when it will be necessary to balance the revolving part of the machine. Should the armature be badly out of balance, the motor will not run. Hence, vigilance begins with the sawing and filing and is carried through to the completion of the job. If, after filing, the builder finds upon measurement that one end of the soft iron piece is wider than the other, he should file it down. A really careful worker will mark the center of the iron and work until it will balance perfectly on the edge of a knife. The next operation is that of bending the armature piece to

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shape. This must be done in a vise and with a hammer. As the work proceeds, the importance of balance is kept constantly in mind. The piece is carefully marked where the bends are to be made.

This done, a hole must be drilled through the exact center of the armature and this should be just large enough to admit the large finishing nail (minus head) that is to be used as a shaft. This member is soldered to the armature frame. If soldering facilities are not available, then the builder will have to seek out assistance in some neighborhood workshop. The best possible accuracy is called for so that the soft iron armature frame will revolve accurately without wobbling.

This latter operation prepares the armature for winding but before this is done, it will be advisable to set the motor bearings up and to test the armature for balance before the wire is wound in place on the two poles. Then if the armature is badly out of balance, it will be an easy matter to set it in the vise and file off metal on the heavy side until balance is restored.

Before the wire is wound in place, the soft iron poles are covered with a single layer of adhesive tape. Exactly the same amount of tape is used on each leg.

A motor of maximum power calls for the use of 100 feet of No. 24 cotton-covered wire on each pole of the armature. This is wound tightly and each turn of wire is made to hug the adjacent turn as closely as possible.

In motors of this type it is required that the wire on the second pole of the armature be wound in place in the opposite direction. Therefore, when the builder begins the second coil, the winding continues in the same way save for this reversal.

No matter how carefully the armature winding is set in place, it will be quite impossible to have the same amount of wire on each pole even though the same number of turns are counted. Therefore, it will be advisable to test again the armature for balance after the windings are completed and the ends of the wire arc temporarily twisted together to prevent unwinding. Testing will usually show that one side of the armature is heavier than the other. This may be easily remedied by the removal of one or two turns of wire which will not seriously interfere with the “electrical balance” required.

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The balancing achieved, the armature is now set aside while we work on the commutator. Should the builder have some shellac at hand, no harm will be done if both coils of the armature arc smeared with it before this member is temporarily set aside.

The next job is going to tax the ingenuity of even the best young mechanics. Should the fellows without a great deal of tool experience find themselves unable to accomplish the work, perhaps the services of dad may be enlisted or it may be that some neighbor handy man will be glad to render assistance.

For the commutator of the motor we must obtain a small piece of brass or copper tubing. The hole in the tube should be about 1/4 inch in diameter and the tube may have an outside diameter of 3/8 of an inch or more. Really the size is not extremely important save that the tubing should not be so large as to be out of proportion with the rest of the motor.

A piece of the 1/2 inch long tubing will be needed for the commutator and it will be necessary to drive a piece of wood doweling (rod) into the tube. A forced fit must be made so that there will be no danger of the dowel coming out later. This done, both ends of the tube are filed so that the wood will be flush with the metal tube.

The builder will now need some tiny brads less than 1/4 inch long and, if they cannot be gotten at the local hardware store, it will be necessary to press ordinary pins into service, cutting them off at the head end.

Perhaps further work should not be done on the motor without a careful examination of the drawing, Fig. 20, which shows the detailed operations for the construction of the commutator. Here it will be noted that four tiny holes are drilled in each end of the commutator tube and that these must be slightly smaller than the diameter of the brads or pins used. The drilling continues on down through the inside wood dowel. It is at this point that a very serious mistake might be made. This commutator is to be mounted on the shaft of the motor and the copper or brass tube forming the commutator should be electrically separated or insulated from the motor shaft. Should the brads or pins pass through the holes in the dowel and contact the motor shaft, the commutator would not function and the motor would not operate. There fore the builder must see to it that the brads or pins do not proceed this far. Yet they should be firmly enough placed to hold the two segments of the commutator to the dowel after the

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segments are formed by the use of a hacksaw. If what is known as a jewelers’ hacksaw can be used for this purpose, a very fine cut may be made. Otherwise, the ordinary hacksaw must be employed. In any event, the worker proceeds with care because the commutator is, after all, a delicate part of the motor.

Fig. 20. The construction plan for “Little Speedy”

The builder is now confronted with the task of drilling a straight hole through the exact center of the wood dowel in the metal tube. This is not quite so easy as it sounds. Either a crooked hole or an off- center hole will cause the commutator to wobble and may even make the motor inoperative.

The best machine to use for such drilling is a lathe but few readers have such elaborate equipment. The next choice is a power drill press but to use this successfully, the ends of the commutator assembly must be perfectly square and the builder is still faced with the rather difficult problem of finding the exact center of the dowel before drilling.

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Fig. 21. A young engineer gives” Little Speedy” a trial run

Should the builder not know a lathe owner in his neighborhood, he should seek out a machine shop. The job is so simple that not more than ten or fifteen cents should be charged, yet the matter is so important that the success or failure of the whole venture depends upon it.

The reader who has carefully followed the instructions, and who learned something from the first chapters dealing with the principles of electric motors, will quickly understand the need of establishing some sort of a relationship between the position of the commutator on the shaft of the motor, the armature coils, and the permanent magnet. After all, our motor will not operate at all unless such a proper relationship is set up. The commutator functions as a revolving electric switch which permits electric current to flow in the right direction through the right coil at the right instant so that the permanent magnetic field may properly interact with the electromagnetic fields set up by the revolving armature coils. We must see to it that the fit between the armature shaft and the commutator is snug enough to prevent a gradual shifting of the latter when the motor is running. Reference to our drawing, Fig. 20, will

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show the proper setting of the commutator in relation to the coils and the permanent magnet.

The making and installation of the brushes is next on the program. The brushes are really sliding contacts that permit the current from the battery to pass through the armature coils. If these brushes are too heavy or press against the commutator too tightly, the little motor will not develop power enough to overcome the friction set up. What we need is light, thin brushes cut from thin sheet copper or brass. They must press very lightly against the commutator, and the commutator as well as the brushes must at all times be kept clean and free from oil.

The bearings for the motor are of the pivot type that we have used in other motors. Such bearings are simple and extremely efficient. They should, however, be cut from thin sheet metal and should not press too heavily against the ends of the motor shaft.

The installation and the adjustment of bearings completes the job and places at our disposal a small motor that will offer many hours of fine service. Little Speedy is really a fine motor, full of pep and always ready to set off on new adventures in electromotive electricity.

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Chapter 7 MAKING THE “ROOFING NAIL MOTOR”

The little “roofing nail motor,” as we shall be I calling it, operates on the same principle as the motor described in Chapter 4. In place of the motion being produced by magnetic attraction for the opposite ends of a soft iron bar, the magnetism generated by the electromagnet applies itself to the successive attraction of four roofing nails driven into an ordinary thread spool which serves as the armature of the little machine. A contactor device is so arranged at the end of the spool that electric current will flow through the electromagnet at just the proper instant, each roofing nail being attracted and pulled forward, in turn.

Construction may as well begin with the armature. The thread spool used is one of ordinary size and the roofing nails are selected because of their large heads. Should the builder not have them handy, there is no reason why 10-penny nails cannot be used when they are cut off to the proper length, which should be in the neighborhood of 1 1/2inches.

Only the rankest kind of an amateur mechanic would attempt to drive such nails directly into the spool which is made of hard wood. Splitting would immediately result. Here the amateur builder must first drill some small holes just under the size of the nails used and these holes must be not only in line but they must also be equidistant. This amounts to 90° for those mathematically able to estimate such things in such terms. Builders should also take care to drive the nails in for the same distance. This keeps the motor armature in balance and contributes to smooth operation.

Now it will be necessary to drive four small contactor pins into one end of the spool or armature. These are located by the use of a compass as illustrated in the drawing and these, like the roofing nails, are located 90° apart. They are, however, so arranged as to be placed midway between the roofing nails. Once more, the builder is warned to drill small holes in the end of the spool before the pins, which may be small finishing nails cut off, are driven in place. These should be left projecting about 1/4 inch.

The next operation should require some soldering but a substitute method may be employed if the builder does not have the necessary materials available or if he lacks the necessary skill. The four pins in the end of the spool must be connected together

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electrically. Should the builder be able to solder, he simply winds a small piece of copper wire around each pin and sets a tiny drop of solder in place over it. If this cannot be done, then the builder may wind the wire around the pins, using several turns for each one, and pinch the wire in place with pliers.

As the builder will note from the drawing, these four pins are also electrically connected to the bearing through the medium of the shaft. Thus, the copper wire connecting the pins, is also connected to the shaft and this in turn contacts the metal strip bearing which has a direct connection with the battery used to drive the motor.

Fig. 22. The construction plan for the motor “roofing nail” motor

Before this connection between the pins and the shaft can be established, it will be necessary to set the shaft in place. The shaft itself may be a large finishing nail with the head cut off and each end filed to a sharp point for use on the pivot bearings illustrated. The electrical connection from the four pins may be soldered or simply squeezed around the shaft.

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Some care must be taken in putting the shaft in place. Here, too, a certain minimum degree of accuracy is called for if a smooth-running motor is to be had. Inasmuch as the hole running through the center of the spool is much larger than the nail, this must be plugged with a piece of wood and drilled so that the nail may be forced through the hole. Should the builder have a power drill in his cellar workshop, this task should be a very simple one. If not, and a hand drill is used, some caution will be needed and some difficulty may be encountered. In any event, we struggle to achieve as much accuracy as possible.

Making the electromagnet is simple enough. A 3-inch carriage bolt is used as the core and this may be bought for about three cents at any hardware store. Adhesive tape is wound in place over the bolt before the wire is wound. The latter may be any size between No. 18 and No. 22, the smaller the wire, the more (in feet) being required.

The bearings may be cut from used tin cans. The dimples or depressions in which the sharpened ends of the shaft revolve are made by the use of a sharp- pointed nail. Some care must be used to see to it that they are both placed at the same height. Both are held in place on the baseboard of the motor with a small wood screw. Care should also be taken to see that the bearings are in perfect line. Otherwise, the shaft will not revolve without a wobble and the motor will fail to reach its maximum speed.

Fig. 23. The “roofing nail” motor complete and ready for business

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The little spring contact member mounted at the end of the baseboard makes electrical contact with each of the four pins as they whizz by. If the motor is to run at high speed, this contact must be very light and the builder will probably have to spend five or ten minutes patiently in making this adjustment. Once this adjustment is made, it will remain set for some time.

Owing to the heavier armature, this little motor should be operated by a battery of two dry cells. To start the motor, the armature is turned until one of the four pins mounted on the end of the spool is in direct contact with the spring member on the end of the baseboard. The electric current is then switched on. Should the motor fail to respond, it may be given some assistance. Failure may mean that the battery is too weak, or that the armature is not able to revolve freely enough.

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Chapter 8 LEARNING TO “DRIVE” ELECTRIC HORSES

Electric horses, even the very smallest ones, are pretty wild and we learn to place bits between their teeth if they are to be kept “on the road.” Otherwise they might run away and do all sorts of damage.

When water flows through a pipe, a faucet placed at the end of the pipe will regulate the flow. The flow of electricity may also be regulated easily and conveniently by the use of simple homemade gadgets, products of our own little workshops.

Most of us already know that electricity is started and stopped with an electric switch. A glance at Fig. 24(A) will quickly demonstrate the simple function of this device. A switch simply removes a small section of the conducting path for electricity when it is “open.” When the switch is “closed,” the electric circuit is complete. Low voltage electricity, such as the kind we use to drive our toy electric motors, can be stopped short in its track by the tiniest gap in the circuit in which it travels.

Fig. 24. How the electric switch and rheostat are made

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The young electrician will want to make himself a simple switch. The little one illustrated in Fig. 24 and in the photograph can be assembled with simple materials and by the use of ordinary household tools. For it, we shall need a small block of wood serving as the base, a few 1/4 -inch strips of thin sheet brass or tin, two 1/2 -inch wood screws, a one-inch (long) machine screw and bolt and half a thread spool which will serve as the handle of the device. Two small washers may or may not be used but they will help hold the metal strips in place more securely if they are employed. They also help the wood screws to serve as binding posts because one wire connection to the switch is placed under each one of the screws.

Fig. 25. The electric switch, the “key” that “opens” and “closes” the electric circuits

When the switch is used with any one of the toy motors described, the young e1çtrician should see to it that the moveable strip is firmly pushed under the stationary one when he wants to close the circuit for the operation of the motor. Otherwise, a bad electrical connection will be made and such connections always cause the loss of a certain amount of electricity. Having so little to use, we cannot afford this.

While such a switch is an excellent “bit” in the teeth of our small electric horse, it has rather bad limitations. After all, it will only start him and stop him. At times, we may wish to make him trot or make him walk. Clearly, no switch will permit this. Something is needed that will regulate the flow of electric current. It is good news that this may be done quite easily.

Perhaps we know that electricity does not pass through all things—glass and silk, for instance. Such things are called insulators. Other things permit a small amount of current to pass. The metals are good conductors, but there is a wide variation between them. Silver and copper are best. Compared with them iron is poor and so is lead.

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Some metals have been mixed together to form alloys and these alloys have what is known as “high resistance” to the passage of electric current. The wire found in our electric toasters and heaters is made from one of these special alloys. This wire has such a choking effect on the current that great heat is produced when the current is forced through it. It is called “resistance wire.” A small length of it may have as much resistance to the passage of electricity as many hundreds or thousands of feet of large copper wire.

Perhaps the young electrician will by now have grasped the principle used in applying resistance wire to the control of electric motors. Doubtless we simply connect a certain amount of this wire in the circuit with the motor. Really, it is not quite so simple as that because arrangements must also be made to vary the amount of the resistance wire in the circuit. Otherwise, the motor would have only one speed (slower) and the user would not have gained complete control. A simple device is needed that will measure out and take in this wire quickly so that more or less of it may be quickly placed in a circuit and removed. One might think that a device designed for this purpose would be expensive and complicated but this is not so.

The reader will agree after the examination of Fig. 24(B). Here the student will find that the resistance wire is wound up in the form, of a long spiral so that a larger amount of it may be placed within a small space. Secondly, it is noted that a moveable metal point or arm is so arranged as to have its end play over the wire spiral forming an electrical contact with it. At the position A, only one half of the resistance wire will be in the circuit. The lines show the path taken by the current. That part of the resistance wire having no current passing through it might just as well not be there. It amounts to a dead end. When the lever of the device is moved to the position shown in Fig. 24(B), only a very small amount of the resistance will remain in the circuit and a short advance from this position will eliminate all of it and still further increase the speed of the motor.

But how much wire will be needed to control the speed of a motor—any motor—? This depends on a number of things: the voltage of the electric current, the number of amperes that must flow, the size and length of the resistance wire and the metals in the alloy.

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Fig. 26. The electric current regulator or rheostat

The device just described is not nameless. It is called a rheostat (re-o-stat). One may be assembled by an amateur electrician in a jiffy. The wire may, during ordinary times, be purchased at the local five- and-ten-cent store for as little as ten cents. It is called Nichrome wire and is intended to supply renewals for electric toasters. Only one half of the spiral purchased will be needed for the purpose.

Should the student be unable to obtain such wire, a 10-cent spool of 22 or 24 iron wire may be had at any hardware store. This may be tightly wound on a pencil until a spiral about three inches long is formed.

The mechanical details of our rheostat will be made clear by an examination of Fig. 24(B). Here it will be seen that another lever similar to the one used on the switch is needed. Three 1/2-inch wood screws and three small washers together with a thread spool and another one-inch machine screw and bolt complete the list of materials. Such a rheostat will permit the motor maker to adjust the speed of his machines from a “run” to a “creep.”

There is still another form of rheostat that may be made by the young motor builder. Perhaps we have heard that water is a good conductor of electricity. Of course, that is only partially true. Chemically pure water will hardly conduct electricity at all. When common table salt or other mineral substances are added to water, however, it becomes a better conductor of current but it does not by any means rank among the best. Really it is not much better than iron. This being so, the young electrician may assemble what is known as a “water rheostat.” This simply involves a water tumbler partially filled

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with water in which a tablespoonful of common salt has been dissolved.

Fig. 27. The plan and assembly of the water rheostat

The form taken by the water rheostat is illustrated in the drawing, Fig. 27. A small water glass is used and one connection to the water is established by means of a small metal plate placed in the bottom of the glass. A wire is connected to this and lead outside the container. This wire must be rubber covered to prevent the passage of current between it and the second or moveable metal plate or electrode, as it should be called.

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Fig. 28. How electric motors are controlled with a rheostat and a switch

Here the electrical resistance in the motor circuit is regulated within wide limits by adjusting the distance between the piece of metal at the bottom of the glass and the moveable piece of metal mounted at the end of the metal rod. The small piece of spring brass fixed to the top of the device and pressing against the rod is used to keep the latter in any position.

Fig. 28 shows how a battery motor, switch and rheostat are connected together for operation. The motor builder should make sure that the switch is left in the “open” position when he completes his work.

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Chapter 9 A REVERSER FOR “LITTLE SPEEDY”

Chapter 8 told us how to control our tiny electric motors. There was a rheostat to regulate speed and a switch with which to turn the current on and off. Now we have another gadget to make; this time a device that will make an electric motor “turn about” so to speak. By its use the armature of the motor will stop and set about revolving in the opposite direction. Unfortunately, this reverser cannot be used with all of the motors described in this book. It will work with “Little Speedy” and the improvised “Cork” motor described in Chapter 5, but it is useless for the others.

The materials required for construction may be found about the household and this might also be said of the tools. A coping saw, a regular saw, a screw driver and a hammer are all that are needed. The wood may be soft pine or, in fact, anything that is clean and handy and that has a thickness of about 3/4 of an inch. The metal used comes from that inexhaustible supply, the tin can. This may be cut to shape with an old pair of scissors if tin snips are not to be had. Of course, the tin should be taken from a fresh container and not from one that is covered with rust.

The coping saw will be needed to cut the disc of wood upon which the two metal or tin plate segments are mounted. Inasmuch as the function or operation of the reverser will not suffer if the wood disc is not truly circular, too much care does not need to be exercised in cutting out this member. It is important, though, that all of the dimensions be carefully followed. Otherwise, upon assembly, we shall find that the four stationary contact members will not touch the moving segments at the correct point and it is important that they should.

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Fig. 29. The construction plans for the current reverser

The segments mounted on the circular piece are held in place by the aid of small brads. Larger nails will in all likelihood split the wood disc. It will not be necessary to drive the heads of these nails below the surface because they are, as will be noted in Fig. 29, placed in such a position as to avoid the stationary contact member when the position of the disc is changed for reversal by means of the handle. This handle may be cut from a piece of 1/4-inch dowel or a short lead pencil may be used if the latter is not at hand. A bit of glue will be all that is needed to hold the handle in place.

Some care should be taken in bending the stationary contacts td shape. Good electrical contacts with the moving members or segments are sought. Good contact means that as large a contacting surface as possible should be established. Perhaps it will be necessary to bend the edges of the stationary members slightly upward so that they will

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not catch the edges of the moving segments as they are turned. A little fussing with this adjustment will produce smooth operation. The wood screw that serves as the shaft for the wood disc also needs careful adjustment. It should not be too tight or too loose. The use of the small washer between the head of the screw and the disc is also necessary. The screw should be just tight enough to prevent shifting of position once the reverser has been operated.

Fig. 30. The reversing switch for “Little Speedy”

Small washers must also be used under the small wood screws holding the stationary contacts in place. These serve in holding the connecting wires. The method of mounting the reverser for Little Speedy is optional. If the builder wishes, he may simply lay the device flat on the table. Mounting in the manner shown in the photograph does permit one-handed operation of the device whereas the other method would require that one hand be used to hold the reverser while the handle is turned with the other.

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Fig. 31. How the current reverser is connected to the motor and battery

Small motors operated with current from one or two dry cells require good electrical connections because of the low voltage of the power source. Little motors of the type described in this book can easily become inoperative because of dirty or loose connections. The connections should be kept as short as possible and tightly clamped or, better, soldered.

When connected as shown in Fig. 31, the operation of the reverser switch is very simple. When it is desired to reverse the motor the handle is simply pushed in either direction as far as it will go.

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Chapter 10 MOTORS IN THE WORKADAY WORLD

Unless we stop to think about it, few of us realize how much our daily life here in America depends upon the electric motor. Millions of them are in constant use, some of them so small that we could cup them in the palm of our hand, others so enormous that 40,000 straining horses would be needed to match their power. Indeed the tiny motors driving our electric clocks are so small that they may be balanced on the end of our thumb. The big fellows that drive our battleships could not be squeezed into our living rooms. Yet fifty years ago very few motors were in use even in our highly advanced country. The steam engine was still supreme and was indeed the power master of the whole world. It had been in the ascendancy since Watt had perfected it back in the latter part of the eighteenth century. But history shows that the steam engine suddenly met a competitive producer of power that was clean, silent and efficient.

Back in the early days, when ‘Watt’s first hissing monsters were installed in the textile mills of England, power was distributed through the use of pulleys and ropes. Crude wooden gears were used when it was necessary to turn corners and most of the power generated by the early engines was lost before it reached the machines that were driven by it. As time went on, these methods of steam power distribution were improved upon and steam engines were perfected but still steam power had many limitations.

It was not, however, until the year I 890 that the electric motor, perfected after sixty years of experiment, was able to challenge the steam engine. That it should challenge it and eventually replace it was patent because the electric motor was a much more practical device. There was no trouble making electricity turn corners. Here was silent power that needed no pipes, no pulleys, no belts nor ropes.

Really the electric motor was able to displace the steam engine long before 1890 but it had to await the perfection of electric generating equipment. After all, powerful electric motors intended for day-to-day use in the workaday world could not be operated from electric batteries. The batteries were far too expensive and they were impractical. The electric motor had to await the development of its sister device, the dynamo or generator which was capable of changing mechanical energy (as from a steam engine or water wheel) directly

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into electric energy. ‘Without dynamos and generators the Electric Age, as we know it today, would not have arrived.

Soon after the perfection of large dynamos, certain alert manufacturers in the United States installed them in their steam power houses. The steam engines, instead of driving long belts leading to the factory, were hitched to the dynamos and electric power from the dynamos was carried to motors located near the machinery to be run. The great central power stations had not yet been built but it was not long before enormous steam-electric and hydroelectric generating stations began to dot America and millions of horsepower began to flow over the copper threads hung high on poles. The great hydroelectric station at Niagara Falls, completed in I 895, supplied power to operate the street cars in Syracuse, i 8o miles away. That was something that Watt’s steam could not have done.

Electricity turned out to be a fluid, easily-managed power. Not only could it turn corners and somersaults, but it could be controlled by the flick of a finger and it left no dust, no dirt. Little wonder they began to call it “white coal.”

Long before the use of electric power in factories became general, the electric street car made its appearance. Old Dobbin, prim’ mover of the early street transports, was gradually replaced by a relatively small iron-encased package of power placed underneath the street cars near the wheels. The electricity needed to operate the “electric horses” was conveyed through the steel rails and a large bronze wire strung over the rails and contacted by what was known as the trolley.

The appearance of even the earliest electric motors, cumbersome, uncertain affairs that they were, inspired inventors. Not a few of them dreamed of powerful, silent electric locomotives streaking across the countrysides in place of the puffing, noisy steam engines. They dreamed, too, of electric street cars to replace the horse cars so widely used between the years of 1870 and 1890.

Thomas Davenport, the inventor of a practical motor mentioned in Chapter i, was one of the first inventors to dream of electric railways. Poor and without large financial support, Davenport had to be satisfied with the construction of a model electric line operated by power from primary batteries. His idea was sound enough but this was in 1834, many years before the larger and more practical dynamos appeared.

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Robert Davidson was another pioneer in the field of electric traction and he was not far behind Davenport. It was in 1838 that he came forward with a full- sized electric engine that was actually given a test run on the Edinburgh-Glasgow R. R. A man named Thomas Hall, of Boston, Massachusetts, also built a full-sized locomotive that performed well considering the rather unreliable source of power.

Many other inventors and would-be inventors tried their skills on the problem of electric traction but real progress was impossible until about the year 1875 when the first large and practical dynamos began to appear.

The first passengers ever to be carried about on a commercial basis toured the grounds of the Berlin Exposition in the year 1879. The machine and its cars were constructed by the great German electrical firm of Siemens and Halsee. The large scale experiment was so successful that the same company built a commercial road between Lichterfeld and Berlin. This operated for many years and attained high speed schedules. This was in 1881.

Thomas Edison constructed a crude electric locomotive at Menlo Park, New Jersey, but the unimaginative railroad officials who saw it said that electricity held no future in the railroad business.

Today we see sleek electric locomotives moving at high speed across the country and the Diesel-electrics, too, have established operating schedules that cannot be maintained by steam engines because of the servicing and solid fuel (coal) problems.

The Diesel-electric carries powerful Diesel motors and these in turn drive electric generators. They supply their current directly to electric traction motors that operate the locomotives. Why not drive the train directly with the Diesel motors? Well, electricity is a far more flexible power; it is easier to handle and control and for these reasons it is practical first to change the Diesel power into electric power.

For these reasons, our battleships are equipped with enormous steam plants. The steam produced by the great boilers is used to drive turbines and the turbines, in turn, drive great electric generators. These supply thousands of horsepower of electric energy to gigantic electric motors that drive the propellers through a series of gears.

The use of such power makes it possible to maneuver the ships much more easily. It also makes it possible to employ the steam

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turbine in place of the steam engine. The former is a much more efficient machine but, unlike the steam engine, its direction of motion cannot be reversed. Electric drive, however, makes reversal easy.

Perhaps one of the most interesting electric trains in the world operates for the C.M. and St.P. railroad over the Rocky Mountains. This is an enormous engine of 5,000 horsepower rating and carries sixteen electric motors in all, one for each axle of the sixteen sets of wheels. The peculiar thing about these motors is that the engineers who designed them arranged matters so that the motors would also serve as generators. When current was fed to them, they were ordinary motors. On the other hand, they generated current, when they were mechanically driven.

After reaching the peak of the Rockies, the road descends many miles, and the locomotives, steam or electric, have to coast. When coasting, then, why would it not be possible to permit the moving locomotive to drive the motors, the motors then acting as generators? That was a simple question and it was answered by the electrical engineers of the General Electric Company who designed and built this first “floating power house” as it has been called. Now, when these great locomotives roll down either side of the Great Divide, the motors are switched over to serve as generators and the generators, in place of taking power from the line, pump it back to help locomotives struggling up the opposite side. Not only that, but the generators require power to turn them and they serve beautifully as brakes.

Fifty years ago, no American home could boast of an electric motor. Now millions of homes have motors, some as many as 20 or 30. Countless millions of motors are used in transportation and industry and even our great transport and military planes carry a number of fractional horsepower motors aloft. It can be truly said that a very large part of our “Electric Age” is supplied by the electric motor.

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