CHAPTER III. A Magnetic Attraction Motor. A Motor Having a Laminated

Field and Armature Frame. How to Make an Experimental Induction Motor. How to Make an Electric Engine.

A MAGNETIC ATTRACTION MOTOR.

This motor differs from those which have already been described, in that no wire is wound on the armature.

*The Field Coils* consist of two electro-magnets wound upon iron cores one and one-eighth inches long and five-sixteenths inches in diameter. Each core is fitted with two fibre heads, one-sixteenth of an inch thick and seven-eighths of an inch in diameter so as to form a bobbin as shown in Figure 33. The bobbins are wound with No. 22 B. & S. Gauge single cotton-covered magnet wire. The magnets are connected in series so that the current flows through them in opposite directions.

*The Armature* is a strip of soft iron one and three-quarters inches long, three-eighths of an inch wide and three thirty-seconds thick. A one-eighth inch hole bored through the center of the armature and the latter forced upon a shaft one and seven-eighths inches long.

The lower end of the shaft is pointed and rests in a small hole in the magnet yoke, half way between the two coils.

The magnet-yoke is a strip of soft Iron or steel two and one-half inches long, seven-eighths inches wide and one-eighth of an inch thick.

The magnets are mounted on a wooden base, five inches long, three inches wide and three-eighths of an inch thick, by means of two 8-32 machine screws which pass upward from the bottom of the base into the bottom of the magnets. The yoke is placed under the’ magnets, between them and the base. The screws pass through two holes, one and one-eighth inches apart.

The armature is supported in position over the electromagnets by means of a standard bent out of a strip of sheet brass. The details of the standard are shown in Figure 36. The standard is fastened to the base by means of two small wood screws.

The armature should just clear the top of the electromagnets when the lower end of the shaft is resting in the socket in the yoke. The shaft should be perfectly vertical and revolve freely without friction.

The lower end of the shaft carries a small brass contact which is forced into position. The exact shape and dimensions of this contact are shown in Figure 37. The holes through the center should be slightly smaller than the diameter of the shaft, so that when the contact is forced into position it will remain secure and not move.

*The Brush* which bears against the contact is illustrated in Figure 38. This is cut out of spring copper or brass and made according to the shape and dimensions shown in the illustration. The brush is fastened to the base by means of a round-headed brass wood screw.

The proper method of assembling the motor and its appearance when finished are best understood from the illustration in Figure 39.

*The Binding Posts* consist of machine screws provided with hexagonal nuts and thumb screws, such as that supplied on dry batteries. One binding post passes through the end of the brush and connects with it. The other binding post is mounted at the left hand forward corner of the base. One terminal of the electromagnets leads to this binding post. The other terminal is placed under the head of one of the screws which hold the standard to the base.

The contact and the brush will have to be most carefully adjusted before the motor will run. The tip of the contact should make contact with the brush just before the armature starts to swing over the electromagnets and break the circuit just as the armature is actually over. The exact position will have to be found by a little experimenting. It is very necessary that the brush should be so adjusted that it only touches the ends of the contact as it swings around.

The operation of the motor is very simple. When a battery is connected to the binding posts the circuit is not complete so that the coils are magnetized and can attract the armature until the contact touches the brush. When the contact and the brush touch, however, the circuit is completed and the armature will be drawn toward the electromagnets. As soon as it reaches a position over the ends of the cores, the circuit should be broken so that the momentum will carry the armature past and around into such position that the opposite end of the contact touches the brush and the operation is repeated.

A magnetic attraction motor of this type will usually have to be started by giving the shaft a twist with the fingers.

HOW TO CONSTRUCT A MOTOR HAVING A LAMINATED ARMATURE AND FIELD FRAME

It is an easy matter to make a strong electric motor suitable to operate on batteries by the exercise of a little careful workmanship.

The field frame and armature of the motor shown in Figure 40 are laminated, that is, built up of separate sheets of iron. They may be made out of sheet tin or ordinary stove pipe iron. The cheapest and simplest method of securing good flat material is to get some old scrap from a tinner’s or plumbing shop.

*The Details of the Field* are shown in Figure 41. The exact shape and dimensions can be understood by reference to the illustration. Lay out one lamination very carefully as a pattern. Cut it out and smooth up the edges, making certain that it is perfectly true to size and shape. Then use it as a template to lay out the other laminations by placing it on the metal and scribing a line around the edges with a sharp pointed needle. Enough laminations should be cut out to make a pile five-eighths of an inch high when tightly pressed together.

*The Armature* is made in exactly the same manner as the field frame, that is, by cutting out a pattern according to the shape and dimensions shown in Figure 43 and using it as a template to lay out the other laminations. Enough should be cut to make a pile five-eighths of an inch high when tightly squeezed together.

The armature is one and three-sixteenths inches in diameter. The hole in the field frame which accommodates the armature is one inch and one-quarter in diameter so that there is a space in between for the armature to revolve in.

The hole through the center for the shaft should be of such diameter that the laminations will force very tightly on a shaft one-eighth of an inch in diameter. The laminations should be very carefully flattened and then forced over the steel shaft which is two and one-eighth inches long. Clean up all the rough edges with a file and smooth the outside so that it will revolve properly in the field without scraping.

Figure 44 illustrates the armature assembled on the shaft and ready to be wound.

*The Armature Windings* consist of four layers of No. 22 B. & S. Gauge double cotton covered magnet wire wound around each leg. The iron should be very carefully insulated with shellaced paper before the wire is put in position so that there will not be any danger of short circuit due to the sharp edges of the metal cutting through the insulation. Each leg should contain the same number of turns of wire and all should be wound in the same direction.

*The Commutator* is illustrated in Figure 45. It consists of a piece of brass tubing seven-sixteenths of an inch long, five-sixteenths inside and three-eighths of an inch outside. It should be forced onto a piece of fibre five-sixteenths of an inch in diameter and seven-sixteenths of an inch long. Split the tube, into three equal parts by dividing it longitudinally with a hacksaw. Make a fibre ring which will force onto the tube very tightly when it is in position on the fibre core and so hold the three commutator sections firmly in position. The sections should be arranged so that there is a small space between each two and they are perfectly insulated from each other. The fibre core should have a one-eighth inch hole through the center so that it may be forced tightly onto the shaft and up against the armature after the windings are in position. The commutator should be in such a position that the split between each two sections comes directly opposite the centre of each winding. Suppose that the windings are lettered "A", "B", and "C", the commutator section between "A" and "B" is numbered 1, that between "A" and "C" is No. 2, and the one between "C" and "B" is No. 3. Then the inside terminal of "B" is connected to the outside terminal of "A" and soldered to the end of commutator section No. 1 close to the winding. The inside end of "B" is connected to the outside terminal of "C" and to commutator section No. 2. The inside end of winding "C" is connected to the outside of "B" and to commutator section No. 3. The connection of the armature windings to the commutator are represented by the diagram in Figure 45.

*The Field Winding* consists of five layers of No. 18 B. & S. double cotton covered wire. A much neater job may be made of this part of the work if two fibre heads are cut to slip over the field and support the ends of the winding as shown in the illustration in Figure 40.

*The Bearings* are illustrated in Figure 46. They are made out of three-eighths inch brass strip one-sixteenth of an inch thick by bending and drilling as shown in the illustration. The location of the holes is best understood from the drawing. The larger bearing is assembled on the field at the side towards the commutator.

Assembling the motor is a comparatively easy matter if it is done properly and carefully. The bearings are mounted on the field frame by screws passing through the holes "B" and "B" into a nut on the outside of the bearing at the opposite side of the field.

The armature should revolve freely without binding and without any danger of scraping against the field. Slip some small fibre washers over the ends of the shaft between the armature and the bearings so as to take up all end play.

*The Brushes* are made of spring copper according to the shape and dimensions shown in Figure 47. They can be cut out with a pair of snips.

Each brush is mounted on a small fibre block supported on the large motor bearing. The holes marked "A" and "C" in the illustration should be threaded with a 4-36 tap. The hole "B" should be made one-eighth of an inch in diameter and drilled all the way through the block.

The holes, "A" and "C" are used to fasten the blocks to the bearing. The brushes are fastened to the blocks by means of a 6-32 screw with a nut on the lower end.

*The Base* is a rectangular block, three inches wide, three and one-half inches long and three-eighths of an inch thick. The motor is fastened to the base by four small right angled brackets bent out of strip brass and secured to the field frame by two machine screws passing through the holes, "H" and "H", into a nut at the opposite end.

One terminal of the field winding is connected to a binding post mounted on the base. The other terminal of the field is connected to the right hand brush. The end of the wire should be placed under the head of the screw which holds the brush to the fibre block. The brush should be on the under side of the block so that it bears against the under side of the commutator.

The left hand brush bears against the upper side of the commutator and is connected to a second binding post on the base of the motor. This makes it a "series" motor, that is, the armature and the field are connected in series.

The motor is now ready to run. Put a drop of oil on each bearing and make certain that the curved portion of the brushes bear firmly against the centre of the commutator on opposite sides. The armature having three poles, should start without assistance and run at high speed as soon as the current-is applied. Two cells of dry or other battery should be sufficient. The motor may be fitted with a small pulley so that its power may be utilized for driving small models.

HOW TO MAKE AN EXPERIMENTAL INDUCTION MOTOR.

A motor having a three-pole armature will run on alternating current as well as on direct current and can be operated on the 110 volt A. C. current in series with a suitable resistance. The average experimenter is probably aware of this but did you know that it can also be operated on alternating current as an *induction motor* and that it will then run *without brushes* and without current being led into the armature?

In order to make an induction motor out of an ordinary three-pole battery motor such as that shown in Figure 48 it is merely necessary to remove the brushes and bind a piece of bare copper wire around the commutator so that it short circuits the segments.

The alternating current should be led into the field coil. A step down transformer will prove very useful for producing a low voltage alternating current which may be connected directly to the field coil. If a transformer is not available, the 110 v. alternating current can be used, provided that a proper resistance such as a lamp bank, be placed in series with the motor.

If the current is turned on and the armature is then speeded up by giving it a couple of sharp twists, or winding a string around the shaft and then pulling it as one would spin a top, the motor will continue to revolve at a good rate of speed.

It may prove easier to start the motor if the armature is speeded up before the current is turned on. As soon as a good speed is reached, turn on the current and the armature should continue to run.

Commercial induction motors are self starting, and are provided with a hollow armature, which contains a centrifugal governor. When the motor is at rest or starting, four brushes press against the commutator and divide the armature coils into four groups. After the motor has attained the proper speed the governor is thrown out by centrifugal force and pushes the brushes away from the commutator. At the same time a metal ring is pressed against the interior of the commutator, short circuiting all the sections and making each coil a complete circuit of itself.

It would be very difficult to provide a small three-pole toy motor with such a governor and short-circuiting device in order to make it self-starting.

It is however possible to accomplish this in another way, by a very simple device.

This consists in providing the armature with another set of coils for use in starting only. The brushes are allowed to remain on the motor but are only used for starting. The leads of the armature winding are removed from the commutator and are all connected together. Then two or three layers of wire are wound over the coils to form new coils which are similar to the old ones but smaller.

These new coils are connected to the commutator in the same way as the old ones were before being removed, just as if the motor was to be used in the ordinary manner.

A two-point switch will be necessary in order to complete the arrangements. The connections should be made as in Figure 49. The switch should be thrown to the right, on contact A, for starting so that the current flows through the field and through the extra coils on the armature in the ordinary way. As soon as the motor has reached its speed, throw the switch to the left so that the current flows through the field only and the motor will continue to run by induction.

HOW TO BUILD AN ELECTRIC ENGINE

An electric engine is really a form of electric motor but differs from the most common form of the latter in that the armature, instead of revolving, oscillates back and forth, like the piston of a steam or gasoline engine. Electric engines are not as efficient as electric motors from the standpoint of the amount of power delivered in proportion to the current used, but they make very interesting models and the young experimenter will derive fully as much pleasure in constructing one as from the construction of an electric motor.

Various forms of electric engines were made before the first practical electric motor was invented. They amounted to little more than curiosities however, and could only be used where the expense of electric current was not to be regarded.

The engine illustrated in Figure 50 is of the double action type. It is provided with two electromagnets arranged so that one pulls the armature forward and the other pulls it back. The motion of the armature is transmitted to the shaft by means of a connecting rod and crank. It is very simple to build and the design is such that it will operate equally well whether it is made large or small. If you do not happen to have all the necessary materials to build an engine according to the dimensions shown in the drawings, you can make it just one-half that size, and it will work equally well although it will, of course, not give as much power.

The complete engine is shown in Figure 50. All the various parts have been marked so that you can easily identify them in the other drawings. It is well to study this illustration carefully so that you will understand just how all the parts are arranged.

*The Base* is illustrated in Figure 51. It is made of a piece of hardwood, seven inches long, three and one-half inches wide, and one-half an inch thick.

*The Electromagnets* will largely determine the dimensions of the rest of the engine. The magnets shown in Figure 52 are made of three-eighths inch round iron two and one-half inches long, provided with two fibre washers one and one-eighths inches in diameter. On end of each of the steel cores is drilled and tapped to received an 8-32 screw. The experimenter may possibly be able to secure some old magnet cores fitted with fibre heads from an old telephone bell or "ringer" as they are sometimes called. A suitable bolt may be made to serve the purpose by cutting it off to the right dimensions with a hack saw. If a drill and tap are not available for drilling and tapping the end so that the core can be properly mounted in the frame of the engine, it is possible, to use the threaded portion of a bolt to good advantage, by the exercise of a little ingenuity. The hole in the frame should then be made larger so that the end of the bolt will slip through, instead of an 8-32 screw and the core clamped in position by a nut on each side.

The fibre washers are spaced two and one-sixteenth inches apart. The space in between should be wound full of No. 18 B. & S. Gauge cotton covered magnet wire. Before winding in the wire, cover the core with a layer of paper so that the wire does not touch the metal. The ends of the wire should be led out through small holes in the fibre heads.

It is not absolutely necessary to use No. 18 B. &.S. Gauge wire in winding the magnets, but it is the size which will give the best results on the average battery. If you use larger wire, the engine will require more current from the battery. If you use finer wire, a battery of higher voltage will be necessary. The current consumption will, however be less.

The electromagnets are mounted in the frame of the engine by means of two screws passing through the holes E and D. The details of the frame are illustrated in figure 53. It is made of a strip of wrought iron or cold rolled steel, five and five-eighths inches long, an inch and one-eighth wide and one-eighth inch thick.

The material for making this part of the engine and also the bearings can best be obtained at some blacksmith shop or hardware store. Heavy galvanized iron can be used but it is not usually thick enough, and it may be necessary to use two thicknesses. The ends of the strip are rounded and bent at right angles so as to form a U-shaped piece with sides one and three-quarters inches high.

The holes, "D" and "E", should be large enough to pass an 8-32 screw. The holes, "A", "B" and "C" should be about one-eighth of an inch in diameter. They are used to pass the screws which hold the frame of the engine to the wooden base.

*The Bearings* are shown in Figure 54. They are made U-shaped and are out of a strip of iron or steel in the same manner as the frame of the engine, but are three-quarters of an inch wide instead of an inch and one-eighth. The dimensions will be understood best by referring to the drawing. The 3/32 inch holes near the top of each side are the bearing holes for the end of the shaft.

The one-eighth inch holes just below are used to fasten the brush holder in position. The holes in the bottom serve to fasten the bearings to the base.

*The Shaft* will probably prove the most difficult part of the engine to make properly. The details are given in Figure 55. It is made of a piece of one-eighth inch steel rod bent so that a crank is formed in the middle. The crank should be bent so that it has a "throw" of one-half an inch, that is, offset one-quarter of an inch so that the connecting rod moves back and forth a distance of one-half an inch. The finished shaft should be three inches long. The piece of steel used should be longer than this and so that it can be cut off to exact dimensions after the shaft is finished. A second crank should be bent in one end of this so as to form an offset contact for the brushes. This second crank will have to be at right angles to the first one and should be much smaller. The ends of the shaft are turned or filed down to a diameter of three-thirty-seconds of an inch for a distance of about the same amount so that they will fit in the bearing holes and turn freely, but not allow the shaft to slip through. The work of making the shaft will require a small vise, a light hammer, files and a couple of pliers. One pair of pliers should be of the round nosed type and the other a pair of ordinary square jawed side cutters. It may require two or three attempts before a perfect shaft is secured. When finished, it should be perfectly true and turn freely in the bearings. The bearings can be adjusted slightly by bending, so that the shaft will fit in the holes and be free, but yet not loose enough to slip out.

*The Armature* is a strip of soft iron, two and one-eighth inches long, seven-sixteenths of an inch wide and three-sixteenths of an inch thick. A one-sixteenth inch slot, three-eighths of an inch long is cut in one end. A one-sixteenth inch hole is drilled through from one side to the other, one-eighth of an inch from each end. The hole which passes through the slot is used tu pass the pin which pivots the armature to the connecting rod. The other hole is used to mount the armature in its bearing. The armature bearing is a small edition of the one which is used to support the engine shaft. The details and the dimensions are given in the lower left hand side of Figure 56. The armature is shown in the center of the same illustration. The connecting rod is illustrated at the right. This is made from a strip of three-sixty-fourths inch brass, three sixteenths of an inch wide and one and five-eighths inches long. The one-eighth inch hole should be drilled close to one end and a one-sixteenth inch hole close to the other.

*The Brushes* are two strips of thin phosphor bronze sheet, two and three-sixteenths inches long and nine thirty-seconds of an inch wide. They are illustrated in Figure 57. The block upon which they are mounted is hard fibre. It is one and five-eighths inches long and three-eighths of an inch square.

It may be possible to secure a flywheel for the engine from some old toy. It should be about three and one-half inches in diameter. A flywheel can be made out of sheet iron or steel by following the suggestion in Figure 58, which shows a wheel cut out of one-eighth inch sheet steel. It is given the appearance of having spokes by boring six three-quarter inch holes through the face as shown. The hole in the center of the wheel should be one-eighth of an inch in diameter. The wheel is slipped over the shaft and fastened in position by soldering.

The parts are now all ready to assemble into the complete engine. Mount the electromagnets in the frame and fasten the frame down to the wooden base so that one end of the frame comes practically flush with the left hand edge of the base. Fasten the bearing across the frame at right angles by a screw passing through the center hole in the bottom of the bearing through the hole A and into the base. The bottom of the bearing should be bent slightly so as to straddle the frame. The bearing should be secured and prevented from turning or twisting by two screws passed through the other two holes in the bottom Use round headed wood screws in mounting the bearing and the frame.

The armature bearing should be mounted on the frame directly between the two electromagnets. Then place the armature in position by slipping a piece of one-sixteenth inch brass rod through the bearing holes and the hole in the lower part of the armature.

Solder the flywheel in position on the shaft and snap the latter into the bearings. Adjust the bearings so that the shaft will turn freely. The connecting rod should be slipped over the shaft before it is placed in the bearings. Fasten the other end of the connecting rod to the armature by means of a piece of one-sixteenth inch brass rod which passed through the small holes bored for that purpose. When the flywheel is spun with the fingers, the armature should move back and forth between the two electromagnets and almost, but not quite, touch the two magnet poles.

All the moving parts should be fitted firmly together but be free enough so there is no unnecessary friction and so that the engine will continue to run for a few seconds when the flywheel is spun with the fingers.

The brushes, supported on their fibre blocks, should be mounted on the bearing by means of two screws passing through the holes in the bearing into the block. The position of the brushes should be such that the shaft passes between the two upper ends but does not touch them unless the small "contact" crank mentioned above is in proper position to do so. The proper adjustment of the brushes so that they will make contact with the shaft at the proper moment will largely determine the speed and power which the finished engine will develop.

Two binding posts should be mounted on the right hand end of the base so that the engine can be easily connected to a battery. Connect one terminal of the right hand electromagnet to one of the binding posts. Run the other terminal of the electromagnet to the brush on the opposite side of the shaft. Connect one terminal of the left hand electromagnet to the other binding post and run the other terminal to the brush on the opposite side of the shaft. Save for a few minor adjustments, the engine is now ready to run. Connect two or three cells of dry battery to the two binding posts and turn the flywheel so that it moves from right to left across the top. Just as the crank passes "dead center" and the armature starts to move back away from the left hand magnet, the small contact crank on the shaft should touch the left hand brush and send the current through the right hand magnet. This will draw the armature over to the right. Just before the armature gets all the way over to the right, the contact should break connection with the left hand brush and interrupt the current so that the inertia of the flywheel will cause it to keep moving and the armature to start to move over toward the left hand magnet at which point the contact on the shaft should commence to bear against the right hand brush, thus throwing the left hand magnet into circuit and drawing the armature over to that side. If the brushes and the cranks are in proper relation to each other the engine will continue to repeat this operation and gradually gain speed until it is running at a good rate.

The appearance of the engine can be improved by painting the metal parts black and the flywheel red. The magnets can be wrapped with a piece of bright red cloth to protect the wire against injury and also lend attraction to its appearance in this way.