Home made toy motors; a practical handbook giving detailed instructions for building simple but operative electric motors

Chapter I

EXPLAINING HOW AN ELECTRIC MOTOR OPERATES. SOME PRINCIPLES OF MAG¬ NETISM. THE DIFFERENCE BETWEEN A SHUNT AND A SERIES MOTOR.

N Electric Motor is a device for transforming electricity into mechanical power. A gener¬ ator, or dynamo, is constructed in almost the same identical manner as a motor but its purpose is just the opposite. A dynamo transforms mechanical power into electricity. A dynamo produces electric current, but a motor consumes it. Some machines can be used either as a motor or dynamo—not all however.

Of course most experimenters have in all probability seen many electric motors, but it is more than likely that the exact operation is not thoroughly understood. Here is your chance to learn.

The little motors described in this book can each be made in two or three hours out of a few scraps of sheet iron, magnet wire and screws. The cost of the neces¬ sary materials is practically negligible.

One of the main advantages of these little motors is that they illustrate the actual principles that are used in the large motors, such as are employed everywhere for practicable power purposes.

The iron parts may be made out of sheet iron or the ordinary so-called “tin” used in cocoa cans, etc. Thin tin can be cut with an ordinary pair of shears. Sheet iron such as is used in making stovepipes, etc., is an excellent material to use in making these little motors. Sheet iron is usually heavier than tin and will have to be cut with a pair of “snips.” Greater skill will also then be required in bending the parts. It is worth while noting however, that the extra difficulty involved in using the heavier material is worth the trouble be¬ cause it makes possible a more powerful and efficient motor.

. The first and easiest type of motor to make is the “Simplex.”

The Principle on which an Electric Motor Operates

is really very simple. If a current of electricity is passed through a copper wire, the wire will attract to itself iron filings, etc., as long as the current continues to flow. As soon as the current is shut off, the filings drop away because the magnetism immediately dis¬ appears with the cessation of the current.

tilings

FIG. 1.—If a current of electricity is passed through a wire, the wire will attract to itself iron filings.

If a wire, carrying a current of electricity is formed into a loop, the entire space enclosed by the loop will possess the properties of a magnet.

By forming the wire into several loops or a spiral the combined effect of all the individual turns is con¬ centrated in a small space and a much more powerful field is produced. If the coil is provided with an iron

VOLTAIC CELL

. FIG - 2 -~If a wire > carrying a current of electricity is formed into a loop, the space enclosed by the loop will become magnetic the arrows represent the paths of the lines of magnetic force.

core, the magnetism is much more concentrated and will exercise a very powerful attactive effect upon any neighboring masses of iron or steel. Such a coil is called an electromagnet.

Electromagnets play a very important part in the construction of electric motors. The strength of an electro magnetic coil is proportional to its ampere turns. The number of ampere turns in a coil is ob¬ tained by multiplying the number of amperes flowing through the coil by the number of turns of wire com¬ posing it.

FIG. 3.—By forming 1 the wire into several loops or a spiral so that the effect of the individual turns is concentrated in a small space, an Electromagnet is made.

You can easily see the effect of turns of wire on an electromagnet by winding two or three turns of wire around a nail and connecting it to a battery. These

FIG 4—The strength of an electromagnet is proportional to the ampere turns. The magnetallustrated above does not possess sufficient turns to be very strong.

two or three turns will probably cieate enough magnetism to enable the nail to lift up one or two ordinary carpet tacks.

Then increase the number of turns to forty or fifty and note that the magnetism of the nail has increased greatly and that it now possesses power to pick up a larger number of tacks at a time.

From this one may be led to believe that the more turns of wire an electromagnet possesses, the stronger it will be, and while to a certain extent this is true* it should be remembered that it is not simply turns that count but ampere turns and if the number of turns of wire is increased beyond a certain point the resistance of the coil to the electric current will be¬ come so great that the current in amperes flowing

FIG. 5.—An increase in the number of turns of wire has re¬ sulted in considerable increase in the magnetism and this magnet is able to lift a much greater weight than that shown in Figure 4.

through the coil is greatly reduced and consequently also the magnetism is decreased.

It will be found that the magnetism of an electro¬ magnet is strongest at the ends. These places are called the poles.

If you bring one pole of a small electromagnet, formed by winding a nail with a few turns of wire, near a compass needle, you will find that it will attract one end of the compass needle and repel the other. The end of the compass needle which points North is called a North pole. The ends of the electromagnet which attracts the North pole of the compass needle is a

South pole.

One of the most important laws of magnetism is that like poles repel each other and unlike poles attract each other. A North and a South pole therefore tend to pull toward each other, whereas two North poles or two South poles repel one another.

Figure 6 illustrates the principle of an electric motor.

It consists of a bar of iron marked “A” called the Armature and wound with a coil of wire called the armature winding. The -armature is the part of the motor which revolves.

FIG. 6.—The Principle of the Electric Motor.

Each end of the armature winding is connected to one half of a brass ring called the commutator and marked “C, C,” in the illustration. The two halves of the commutator are insulated from each other and are mounted on the armature shaft so that they revolve together with the armature.

The armature revolves between the ends of a horse¬ shoe shaped piece of iron called the field. The field is also wound with a coil of wire called the field winding or sometimes the field coil.

The armature and the field are both electromagnets.

Two strips of copper, “B, B,” bear against the commutator. These are the brushes, and their purpose is to.lead the current to the armature coil.

One brush is connected to one end of the field coil. The other end of the field coil and the other brush are connected to a source of electric current.

As soon as the current is turned on, the armature and the field both become magnets. The North pole of the field attracts the South pole of the armature and vice-versa. The armature starts to move so that the poles will come opposite but as the commutator moves around and is turned over, the current flows through

SHUNT SERIES

FIG. 7.—Diagrams showing the difference between a Shunt and a Series Motor.

the armature coil in the opposite direction. This re¬ verses the magnetism of the armature and that which was the South pole become the North pole and vice-versa.

The armature poles will therefore have to move 180 degrees in order that the South pole may come oppo¬ site the North pole of the field. Before it gets there, however, the commutator will have turned over again, reversing the current in the armature and making it necessary to continue its journey again. This process

HOME MADE TOY MOTORS J keeps up and so the armature revolves always trying to seek a new position which it is prevented from re¬ maining at by the action of the commutator.

Motors are said to be series or shunt wound depend¬ ing on whether all the current flowing through the armature also passes through the field or whether it divides between the two as shown in Figure 7.

Chapter II. The Construction Of Simple Toy Electric Motors

TP HE Simplex Motor is an interesting little toy A which can be made in a couple of hours, and when finished it will make an instructive model.

As a motor itself, it is not very efficient, for the amount of iron used in its construction is necessarily small. The advantage of this particular type of motor and the method of making it is that it demonstrates the actual principle and the method of application that is used in larger machines.

FIG. 8.—Details of the Armature for the Simplex Two-pole Motor.

The field of the motor is of the type known as the ‘‘simplex/’ while the armature is the “Siemen’s H” or two-pole type. The field and the armature are cut from ordinary tin-plated iron, such as is used in the manufacture of tin cans and cracker boxes.

The simplest method of securing good flat material is to get some old scrap from a plumbing shop. An old cocoa tin or baking-pow r der can may, however, be cut up and flattened and will then serve the purpose almost as well.

The Armature —Two strips of tin, one-half of an inch by one and one-half inches,, are cut to form the arm¬ ature. They are slightly longer than will actually be

FIG. 9.—Showing the Armature assembled on the shaft ready for winding.

necessary, but are cut to length after the bending operations are finished. Mark a line carefully across the center of each strip. Then taking care to keep the shape symmetrical so that both pieces are exactly alike, bend them into the shape shown in Figure 8. The small bend in the center is most easily made by bending the strip over a knitting-needle and then bend¬ ing it back to the required extent.

A piece of knitting-needle one and seven-eighths inches long is required for the shaft. Bind the two

FIG. 10.—A front view of the Field Frame.

halves of the armature together in the position shown in Figure 9. Bind them temporarily with a piece of iron wire and solder them together. The wire should be removed after they are soldered.

The Field Be nr tyro Proper Shape

FIG. 11.—The completed Field Frame, ready for winding.

The Field Magnet is made by first cutting out a strip of tin five-eighths of an inch wide by five inches long and then bending it into the shape shown in Figure 11. The easiest way of doing this with the most accuracy is to cut out a piece of wood as a form, and then bend the tin over the form. The dimensions shown in Figure 10 should be used as a guide when making the form.

FIG. 12.—The Bearings.

Two small holes should be bored in the feet of the field magnet to receive No. 8 wood screws, the pur¬ pose of which is to fasten the field to the base.

The Bearings are shown in detail in Figure 12. They are easily made by cutting from sheet tin. Care should be taken to make the bearings accurately so that the armature will be in the proper position when the motor is assembled. Two small washers, serving as collars, should be soldered to the shaft as shown in Figure 13.

The Commutator Core is formed by cutting a strip of paper three-eighths of an inch wide and about five inches long. It should be given a coat of shellac on one side and allowed to dry until it gets sticky. The strip is then wrapped around the shaft until its diam¬ eter is three-sixteenths of an inch. The sticky shellac should be sufficient to hold the paper tightly in position when dry.

The Base is cut from any ordinary piece of wood and is in the form of a block about two and one-half by one and seven-eighths by one-half inches thick.

FIG. 13.—Side view of the Armature and Commutator Core assembled on the Shaft before winding.

Assembling the Motor —The parts must be carefully prepared for winding by covering with paper. Cut a strip of paper five-eighths of an inch wide and one and three-eighths inches long and give it a coat of shellac on one side. As soon as it becomes sticky, wrap it around one of the two upper vertical parts of the field magnet as indicated in Figure 11. Both sides of the field should be insulated with paper in this manner. The armature is insulated in exactly the same way, taking care that the paper covers the entire flat portion.

The field and armature are now ready for winding.

It is necessary to take proper precautions to prevent the first turn from slipping out of place.

The field should be wound first. This is accom¬ plished by looping a small piece of tape or cord over it at the point indicated by “A” in Figure 15. The next two tufns are then taken over the ends of the loop so as to embed them. Wind on three layers of wire on one side and then run the wire across to the other side and wind on three layers there. The third layer of wire in the second coil should end at “B.” It

FIG. 14.—Showing the Motor assembled on the Base so that all the parts may be lined up before winding.

should be fastened into position by a loop of string so that it will not unwind.

This method divides the field winding into two parts, both of which are connected together. The outside layer of the first coil is connected to the inside layer of the second coil. The two coils really form one con¬ tinuous winding divided into two parts. After the winding is finished, give it a coat of shellac.

The winding of the armature is somewhat more difficult. The wire used for winding both the armature and the field should be No. 25 or No. 26 B. & S. Gauge double cotton-covered.

In order to wind the armature, cut off about seven feet of wire and double it back to find the center. Then place the wire diagonally across the center of the arm¬ ature so that there is an equal length on both sides. Place a piece of paper under the wire at the crossing point to insulate it. Then, using one end of the wire, wind four layers on half of the armature. Tie the end down with a piece of thread and wind on the other half.

The ends of the wire are cut and scraped to form the commutator segments. Figure 17 shows how this is done.

FIG. 16.—The Armature Winding before the Commutator is completed. _

Bend the wires as shown so that they will fit closely to the paper .core. Bind them tightly into position with some silk thread. Use care so that the two wires do not touch each other. Cut the free ends of the wire off close to the core.

When finished, the relative positions of the armature and the commutator should be as shown in Figure 17.

Figure 14 shows how the motor is assembled. The windings are not shown for the sake of clearness. The armature should be exactly in the center of the field. The bearing holes should be in the correct position and should permit the armature to revolve freely.

TO FORM COMMUTATOR ARMATURE

FIG. 17.— The completed Armature showing how the Commu¬ tator is constructed.

The armature should not scrape against the field at any point, but should clear it by about one-sixteenth of an inch.

The brushes are made by flattening a piece of wire by a few light hammer blows.

The brushes are fastened under a small clamp formed by a strip of tin held down at each end with a wood screw. They can be adjusted to the best advantage only under actual working conditions when the current is passing through the motor. One or two dry cells should be sufficient to operate the motor.

The completed motor is shown in Figure 19.

One end of the winding is connected to one of the brushes. The other brush and the other end of the field form the terminals to which the battery is con¬ nected.

The motor, being of the two-pole armature type,

FIG. 18 .—Details of the Commutator.

must be started when the current is turned on, by giving it a twist with the fingers.

Put a drop of oil on the bearings, make sure that the brushes bear firmly but not tightly against the com¬ mutator, connect the battery and your motor is ready to run. It will spin at a high rate of speed.

SIMPLEX MOTOR WITH THREE-POLE ARMATURE.

The form of “Simplex” motor which has just been described has only one drawback which prevents it from being a first class motor in every respect, namely, the armature has only two poles and the motor is therefore not self-starting, but must be given a twist with the fingers in order to start it rotating. A Two-pole armature is the easiest for the young experimenter to make and that is the reason that it has been de¬ scribed first.

All large power motors are provided with armatures having a large number of poles so as to be self-starting and to give as steady a pull as possible.

The Armature —The method of making a three-pole armature is practically the same as that of making one having only two poles. Three strips of tin, one-half an inch by one and one-half inches are necessary. They are purposely made a little longer than is actually required in order to form the armature and are cut to length after the finish of the bending operations.

Side View End View

FIG. 20.—Details of the Three-pole Armature.

Mark a line carefully across the center of each strip. Then bend them into the shape shown in Figure 20, taking care to keep the shape symmetrical so that all three pieces are exactly alike. The bend in the center which must fit over the shaft is most easily made by bending the strips over a knitting-needle and then bending them back the required amount.

The Shaft is formed by a piece of knitting-needle, one and seven-eighths of an inch long. Assemble the three pieces, forming the armature, on the shaft as shown in Figure 21. Bind them temporarily together with a piece of iron wire and then solder them along the edges. The iron wire should be removed after they are soldered.

The Commutator Core is formed by cutting a strip of paper, three-eighths of an inch wide and about five

FIG. 21.—The Three-pole Armature assembled on the shaft.

inches long. It should be given a coat of shellac on one side and allowed to dry until it becomes sticky.

The strip is then wrapped around the shaft until its diameter is three-sixteenths of an inch. The sticky shellac should be sufficient to hold the paper tightly in position when dry and to form a hard, firm core.

The illustration in Figure 22 shows the position of the core on the shaft in relation to the rest of the armature.

The Winding of the Armature may seem somewhat more difficult at first than was the case with the two-pole armature, but it is really very easy. The wire used for this purpose should be No. 25 or No. 26 B. & S. Gauge, double cotton-covered. Single cotton-covered wire for this purpose is liable to give trouble on ac¬ count of short circuits.

In order to wind the armature, cut three pieces of wire about three and one-half feet long. Wrap a strip of paper around each section of the armature so that the sharp edges of the tin will not cut through the in-

FIG. 22.—Showing the Armature and Shaft with the Commu¬ tator Core in position.

sulation on the wire and then wind four layers of wire on each section of the armature.

Each section should be wound in the same direc¬ tion as the others. The ends of the wires should be scraped free from insulation and connected together as follows: Connect the outside end of one section to the inside end of the next section. We will presume that the three sections of the armature are lettered “A, B, and C.” Connect the outside end of “A” to the inside of “B”; the outside of “B” to the inside end of “C” and the outside of “C” to the inside of “A.”

Those portions of the wire forming the connections between the three sections, are used to form the com¬ mutator segments, in the same manner as the ends of

FIG. 23 .—Diagram showing how the coils are connected to¬ gether so as to form a continuous winding.

the wires in the case of the two-pole armature, only in this instance there are three sections to the arm¬ ature.

Bend the wires so that they will fit closely to the paper core and bind them tightly into position with some silk thread. A section of the commutator should come opposite the space between each section of the armature.

The Field Magnet is exactly like that used in mak¬ ing the Simplex motor with the two-pole armature. It is made by first cutting out a strip of tin five-eighths of an inch wide by five inches long and then bending it into the shape shown in Figures 10 and 11. The easiest way of doing this with reasonable accuracy is to cut out a piece of wood for a form and then bend the tin over the form.

Two small holes should be bored in the feet of the field magnet so as to enable the field to be fastened to the base.

The field is wound with the same size of wire used on the armature. The winding is started by looping a small piece of tape or cord over the frame at the point indicated by “A” in Figure 15. The next two turns are then wound over the ends of the loop so as to hold them down. Wind on three layers of wire on one side and then run the wire across to the other side and wind on three layers there. The third layer of wire in the second coil should end at B. It should be fastened in position by a loop of string so that it will not unwind.

This method divides the field winding into two parts, both of which are connected together. The outside layer of the first coil is connected to the inside layer of the second coil. The two coils really form one con¬ tinuous winding divided into two parts. The illus¬ tration in Figure 23 should make this clear. After the winding is finished, give it a coat of shellac.

The Bearings are shown in detail in Figure 12. They are easily made. Care should be taken to make the bearings very accurate so that the armature will be in the proper position when the motor is assembled.

Two small washers, serving as collars to bear against the inside of the bearings and keep the armature in the field should be soldered to the shaft as shown in Fig¬ ure 13.

The Base is cut from any ordinary piece of wood and should be in the form of a rectangular block about two and one-half inches by one and seven-eighths inches wide, and one-half inch thick.

The completed motor is shown in Figure 24. Be sure that the armature does not scrape against the field at any point but clears it by about one-sixteenth of an inch all around. The brushes are fastened under a small clamp made from a strip of tin held down at each end by a small wood screw. The brushes are made by flattening the end of a piece of copper wire with a few light hammer blows. The brushes can be best adjusted under actual working conditions when the current is passing through the motor.

One end of the field winding is connected to the brush marked “C,” in Figure 24. The other brush, “A” and the other end of the field winding, “B,” form

FIG. 24.— The completed Three-pole Motor.

the terminals to which the battery is connected. This forms what is known as a series connected motor, be¬ cause the armature and the field are in series and the current must pass from one to the other.

After you have finished assembling the motor, put a drop of oil on the bearings, make certain that the brushes are properly adjusted, connect the battery, and your motor is ready to run. One or two dry cells should furnish sufficient current to run the motor at high speed.

HOW TO MAKE THE SIMPLEX OVER¬ TYPE MOTOR.

The method of construction which has been out¬ lined in making the two Simplex motors, just described, also lends itself to the construction of many other simple and interesting forms of motors.

Figure 25 shows a form of motor which is essentially the same as that shown in Figure 24 except that the field has been turned upside down and the armature is at the top of the motor instead of the bottom.

FIG. 25 .—The Simplex “Overtype” Motor.

The detailed dimensions of the field are shown in Figure 26. It is made by cutting out a. strip of tin five-eighths of an inch wide and five inches long. This strip is then bent into the shape shown in Figures 26 and 27. This form of field is really very similar to that shown in Figure 15 except that the two feet are omitted and it has been turned upside down. The method of making ft is the same.

The field should be wound with either No. 25 or No. 26 B. & S. Gauge double cotton-covered wire. It

Front View o? Field

FIG. 26.—Details of the Field Frame for the “Overtype” Motor.

should be carefully prepared for winding by a strip of shellaced paper around each of the two straight parts of the field magnet where the winding is to be placed. Then proceed with the winding in exactly the same manner as in the case of the field shown in Figure 15.

The armature used is of the the three-pole type and is exactly the same as that shown in Figures 20, 21 and 22.

The bearings will have to be made much higher on

The Field Bent into Proper Shape

SHOW/NO FIELD WINOINO

FIG. 27— Showing how the Field is Wound.

account of the armature being higher than the base.' The details of the bearings are shown in Figure 28. They are cut out of sheet tin. Care should be taken to make them accurately so that the armature will be in the proper position when the motor is assembled.

The base is a block of wood two and one-half inches long, one and seven-eighths of an inch wide and one-half inch thick.

The field is fastened to the base by four small wood screws. The exact method of assembling the motor is probably best understood by studying the illustra¬ tion in Figure 25.

Front View

FIG. 28.—The Bearings.

THE MANCHESTER MOTOR.

Those readers who have made the motors already described, are no doubt anxious to proceed with the construction of some models which bear a greater re¬ semblance to the large motors commonly employed to furnish power.

Figure 29 shows a motor of the “Manchester” type.

The Field of this machine is made from a strip of heavy sheet tin, one-half inch wide and about six inches long, bent to shape and joined in the center of the bottom pole piece, just above the pedestal. It is best to cut the strip a little long and then reduce it to the exact length required after the bending operations have been finished. The illustration in Figure 30 shows the details and dimensions of the field.

The field should be bent into shape with the aid of a pair of pliers and a wooden form, in the same manner employed in making the motors already described.

The field frame is supported by a “pedestal.” The pedestal is formed by another strip, one-half inch wide, soldered to the field at right angles, underneath the joint in the lower pole piece.

The pedestal should be firmly soldered to the field, care being taken to see that the solder runs well into the joints. Then bend the ends of the pedestal down to form two “feet” as shown in the illustration. The feet should be bent so as to bring the center of the armature tunnel five-eighths of an inch above the base.

Two small holes should be bored in the pedestal, at each side, so that the motor can be screwed fast to a woode base.

Winding the Field—It will be necessary to proceed with the winding of this motor in a slightly different

•f

Front View

FIG. 30— Details of the Field Frame.

manner from that followed in making the other motors. The wire cannot be wound on as easily as before and it will be necessary to wind the required length of wire onto a small spool or bobbin, which can be passed through the field. Double cotton-covered wire is the best for the purpose. Either No. 25 or No. 26 B. & S. Gauge may be used. A strip of paper should be wrapped around the field frame at all points where the wire is liable to touch, so as to guard the insulation against possible abrasion.