Designs for small dynamos and motors

Preface

MOST of the chapters of this book originally formed articles written for the American Electrician, and many of them were published in the book entitled " Electrical Designs." Chapters X to XVIII inclusive, however, have not previously appeared in book form, and all of the direct- current designs herein described have been revised in accordance with the changes in the practice of dynamo and motor design which have occurred since their first publication.

The majority of the designs were prepared with a view of reducing to the simplest degree the facilities necessary for the construction of the machines, rather than to secure the most graceful outlines or best efficiency.

Chapters XIX to XXII inclusive describe designs by Mr. J. C. Brocksmith which were previously described in issues of the American Electrician that are now out of print. These were also reprinted in ''Electrical Designs," which is superseded by the present book and three others now in press. The other volumes are devoted, one to electrical instruments, telephones and similar light constructions, another to heavier electrical apparatus other than dynamos and stationary motors, and the third to gas engines and other machinery not involving electrical construction. These volumes will contain all of the material that appeared in "Electrical Designs," excepting that contained by the present book, together with much additional matter not heretofore printed in book form.

C. P. P.

NEW YORK, December i, 1905.

789547

Contents

CHAPTER PAGE

I. ONE -SIXTH HORSE-POWER MOTOR WITH DRUM ARMATURE ... i

II. ONE-SIXTH HORSE-POWER MOTOR WITH RING ARMATURE ... 8

Chapter I One-sixth Horse-power Motor With Drum Armature

IN preparing this design and those which follow, it has been assumed that any one who is sufficiently interested in the subject to undertake the construction of a motor or dynamo will be sufficiently familiar with electromechanics to exercise individual judgment in the matter of fitting the various parts, and also in the design and construction of brush holders, terminal blocks, and such other parts as are not of controlling importance in the electrical design of the machines. Detailed descriptions of these parts will, therefore, not be given; the reader may easily inform himself concerning these, if necessary, by inspecting a finished machine of almost any type, or by reference to any good text-book.

FIG. i

The accompanying sketches are intended to serve as working drawings in the construction of a J horse-power motor, for operation upon a i lo-volt direct-current circuit. In Figs, i and 2, M is the field magnet, consisting

i

FOR SMALL DYNAMOS AND MOTORS of a bar of wrought iron or mild steel 3 ins. wide and ij ins. thick, bent into the shape shown; the inner surface of each limb is machined smooth a distance of three inches, forming shallow mortises to receive the pole-pieces, P P, which are secured by J-in. cap screws passing through the magnet limbs. The pole-pieces, P P, are of gray cast iron, and should be finished on all sides to remove the scale as well as to improve the appearance of the completed machine. The magnet, M, might be made to look neater by touching up its sides on a coarse emery wheel; it should be well annealed after bending and finishing.

Two holes, h, h, are bored through the pole-pieces, after these are fitted to the magnet, but before the armature chamber is bored out. These holes are 17-64 in. diameter, and they must be 3! ins. apart, center to center, and equidistant from the center of the armature chamber; if the magnet limbs conform strictly to the measurement given from face to face of the finished part of the limbs, the centers of the holes, h, h, will each be 3-16 in. from the joint between the magnet and the pole-pieces. In these holes are to be inserted J-in. iron or steel rods 7 J ins. long, threaded at each end a distance of f in. Fig. 2, which gives a plan view of the

(D

C)

O o o p.

FIG. 2 magnet and the journal yokes, F, F, shows the function of these rods; they support the yokes and carry distance-pieces, c, c, d, d, made of brass tubing just large enough to slip over the rods, and having J-in. walls. The pieces, c, c, are if ins. long, and d, d, are 2\ ins. long. The yokes are held in place by brass nuts, not shown in Fig. 2.

ONE-SIXTH HORSE-POWER MOTOR WITH DRUM ARMATURE 3

-; The journal yokes, F, F, are alike. They are of cast brass, J in. thick, with a stiffening rib | in. thick, on each side of the journal box. The inner endfc)f one box should be trued up to receive the brush arm or quadrant. The yokes may be much more easily and accurately fitted if a steel template is used. This may be cheaply provided by taking a piece of flat steel, i in. wide and 4^ ins. long, scribing a straight line approximately down the center, and drilling three holes as shown by T; Fig. 2, the center one 11-16 in. and the others J in. in diameter. After the box is bored, mount it on a mandrel and turn down the inner end to fit the center hole in the template T, and at the same time face up the ends of the yoke where they are to touch the distance-pieces; put the template on the end of the box and scribe the positions of the J-in. holes on the ends of the yoke. This template should also be used to fix the distance apart of the holes, h, h (Fig. i). The boxes are bored out 9-16 in. in diameter and fitted with bushings of J in. bore and i in. long; oil grooves should be cut at each end of the box and provision made for taking out the oil. Oil cups may be used to feed the bearings.

After the yokes are fitted the frame may be centered in a lathe as follows, for boring out the pole-pieces. Take a piece of f-in. round machinery steel i.i ins. long, and make the shaft 5 (Fig. 3); the distance from e to g is 3^ ins. and the diameter there is f in.; from g to i is 3 11-16 ins. and the diameter J in.; from i to j is i 1-16 ins. and the diameter f in.; from j to k is 3 ins., and the diameter is f in. Turn the ends of the shaft down to a point, like that of a lathe center; put it in the boxes, bolt the yokes in place, and then put the frame on the lathe carriage, adjusting it until the sharp ends of the shaft are in exact line with the lathe centers. Bolt the motor down in this position, remove the yokes and shaft, and bore out the pole-pieces. The ends of the shaft should afterwards be squared off, care being taken to cut exactly J in. off each end, leaving the shaft 10 ins. long.

The armature (Fig. 3) is built up of iron discs 3 ins. in diameter and not more than 1-32 in. thick; there are twelve slots, each 3-16 in. wide and f in. deep. These may be punched in each disc separately, if a stamping press is available, or they may be milled after the discs are assembled on the shaft. If the slots are milled the discs should be taken off the shaft afterwards and the burrs dressed off, care being taken to reassemble them exactly as they were when the slots were milled; this may be accomplished by taking a very slight cut with a metal saw along the top of one tooth, using the mark as a guide to get the proper slots together. In order to get them in exact alignment, a rectangular bar of metal should be made to fit snugly in one slot before taking the discs off; when they are put back this bar is inserted in the slot to which it was fitted and the nut is set up hard. End plates, W W, of brass, 2 ins. in diameter and 3-16 in. thick, serve to prevent the end discs from buckling when they are compressed. A nut (not shown), fitted to the thread which begins at g on the shaft, serves to clamp the discs, which are held at the other end by the shoulder, i ; no key is necessary to prevent the discs from turning on the shaft in so small a machine, but it is essential that they should be clamped as tightly as a fairly strong man can clamp them, using a six-inch wrench on the nut. The shaft may be held in a pipe vise between i and / when setting up the nut; the nut should be made of very hard bronze metal in preference to steel, as the latter attracts magnetic lines of force and is liable to heat.

The commutator may be made as shown in the sketch, or according to any other modern plan, a number of which were described in the t

s

p

FIG. 3

American Electrician for July, 1896. The only essential features are the space along the shaft which must not exceed f in., the width of face, which should not be less than \ in., and the number of segments, which must be 24. The commutator here shown is intended to be secured to the shaft by a small steel set-screw through the hub or boss at the front; the end of this hub, /, must be i J ins. from the end of the shaft. Extreme care must be taken to insulate the segments from the shell as well as from each other; mica is the only reliable material for this purpose. Carbon brushes \ in. wide and J in. thick should be used.

The armature core is next prepared for winding. Cut four discs of heavy drilling (so-called twilled muslin), 2\ ins. in diameter, with a f-in. hole in the center; varnish the ends of the armature core with shellac and

ONE-SIXTH HORSE-POWER MOTOR WITH DRUM ARMATURE varnish two of the cloth discs, each on one side; thread them on the shaft, one at each end, with the varnished sides next to the core, and press them tightly on the core. While the varnish is hardening cut 24 pieces of drilling the shape of t (Fig. 3); cut two slits \ in. long in each end, 9-16 in. from each side, and 3-16 in. from each other; varnish the strips on one side, and when nearly dry bend them along the dotted lines so as to form troughs, with the varnish inside the trough. Varnish the outside of each trough and the walls of the slots in the core; put two troughs in each slot and turn the flaps, u, v, w, flat against the end of the core, applying enough fresh shellac to hold them down. Then put on the two remaining end discs of cloth, first varnishing the sides next to the armature; after they are in place varnish the outsides and put the core in an oven to bake, being careful that the oven is not hot enough to scorch the cloth. A temperature of 130 degs. Fah. is sufficient. After baking, tape the shaft

Une

FIG 4 thoroughly from i to j, and from the other end of the core to where the commutator will come.

The coils consist each of 20 turns of No. 24 double-silk-covered wire, wound 5 turns wide and 4 deep in the slots, but spread out as flat as possible across the heads. Wind coil No. i in slots, A A'-, coil No. 2 in B B'; No. 3 in C C'\ No. 4 in D D' \ No. 5 in E E'rand No. 6 in F P. Coil No. 7 goes in A ' A, on top of coil No. i, but beginning on the opposite side of the core, as indicated by the lettering; No. 8 in B' B] No. 9 in C' C; No. 10 in D' D- No. n in E' E, and No. 12 in F' F. Coils 13 to 24 are wound on top of the first 12 coils in exactly the same order. After winding each coil bring the finishing end across to the slot where the starting end enters and twist the two lightly together. When all the coils are on untwist the coil ends and twist the last end of each coil to the starting end of the coil in the slot next to it on the right ; these twisted ends go each to a commutator segment, in regular order.

FIG. 6

The field magnet is easily made ready to wind by taping the horizontal part of the magnet, two layers deep, with varnished muslin and putting on two fiber heads. One of these heads is shown by H (Fig. 4). It is in two pieces, the seams being at the ends, and is cut from J-in. sheet fiber. The two halves may be clamped together on the core by means of a small brass wire drawn around the outer edge, laying in a shallow groove, the ends being twisted and cut close. The pole pieces should be removed before taping and putting on the heads, to facilitate these operations as well as the winding of the coil. One fiber head has a notch, n, half way of its inner long side, to enter the field wire. The coil consists of No. 28 single- cotton- covered wire, B. & S. gage, f in. deep and the full length of the available space. At least 9,500 turns should be got on. The field winding is connected in shunt to the brushes, and it would be a good plan to provide a starting switch and resistance lamp connected up as shown diagrammatically by Fig. 5, where F is the field coil, B B the brushes, L a 32-candle-power, loo-volt incandescent lamp, S the starting switch, m a magnet, and S W a double-pole snap switch. This arrangement could be mounted on the base of the motor. Fig. 6 shows

ONE-SIXTH HORSE-POWER MOTOR WITH DRUM ARMATURE 7

the complete motor on a wooden base, Q, without the pulley; the latter may be any diameter between ij ins. and 2j ins., with a i-in. crown face or J-in. grooved face. The motor is secured to the base by flat-head machine screws from below, entering the ends of the wrought iron and countersunk in the under side of the wood. This machine will stand a momentary overload of 100 per cent, and will work up to J horse-power for half an hour at a time.

WINDINGS FOR BATTERY SERVICE

In order to adapt this motor for use in connection with a battery the following windings, etc., must be substituted for those specified above: The armature to be wound with six coils of No. 12 wire, each having twelve turns (three wide and four deep in a slot). The field wire will be No. 19, wound 17 layers deep and 83 turns in length. The commutator will have six segments, and should have a brush surface f in. wide; copper brushes f x J in. should be used, the contact faces being cut to such a bevel as to present an area of J in. square at least. Connect the field winding in shunt with the armature, instead of in series as is usually done. This winding is for 6 volts. The machine thus wound will stand an armature current of 20 to 25 amperes.

Chapter II One-sixth Horse-power Motor With Ring Armature

IN Figs. 7 and 8 M is a wrought-iron magnet core, P P cast-iron pole-pieces, C the armature core, and Y the journal yoke. The magnet core, M, is made from a i in. x 4^ in. bar of commercial wrought iron bent to the shape shown. The faces of the arms are machined to a depth of 1-16 in., where the pole-pieces, P P, are attached, so as to form a magnetic joint of as low reluctance as possible. The pole-pieces are secured to the magnet arms by J-in. cap screws passing through smooth holes in the arms and tapped into the pole-pieces; the latter are of gray cast iron, and should be finished on all sides sufficiently to remove the scale. The magnet, M, might be improved in appearance by touching up its sides with a coarse emery wheel ; it should be thoroughly annealed after bending and finishing. It will be noticed by reference to Fig. 8 that the ends of the magnet arms project slightly beyond the outer faces of the pole-pieces; this is done in order to furnish a guide for the flanges of the journal yoke arms. After fitting the pole-pieces to the magnet arms the complete magnet frame is bolted to the lathe carriage in position for boring out the pole-pieces; before this is done it is necessary to drill a hole through the back of the magnet to allow the boring bar to pass through, and also to form a seat for the rear bearing. This hole is i in. in diameter, and the magnet frame must not be allowed to move from its original position on the lathe carriage from the time the hole is drilled until all the circular tooling on it is accomplished.

After drilling the hole in the back of the magnet adjust the boring bar and bore the armature chamber out, 4 11-16 ins. in diameter. Next adjust the boring tool so that it will scribe on the ends of the magnet arms arcs of a circle 6 ins. in diameter; then cut away the wrought iron inside the scribed marks, down flush with the pole-pieces, as shown in Fig. 7, forming recesses for the flanges of the journal yoke. The yoke and box are cast in one piece of brass or other non-magnetic composition; the shell of the box is ij ins. long, and projects J in. beyond the inner face of the yoke; the outer diameter of the shell is i in., and it is bored out to

ONE-SIXTH HORSE-POWER MOTOR WITH RING ARMATURE 9

f in. inner diameter and bushed to f in. The yoke and arm portions are 3-16 in. thick, with a J-in. stiffening rib on each side of the box, and the arms taper from i in. wide at the flanges to about J in. near the box. The flanges are 2 ins. long, f in. wide, and \ in. thick after facing; the arms, beyond the bends, are sufficiently long to make the distance from the face of the pole-piece to the inner face of the yoke 2 ins. After boring the box it is mounted on a stiff mandrel and the surfaces of the flanges that go next the magnet are faced up true ; next, the outer edges of the flanges are skimmed off until the yoke fits snugly between the curved edges of the recesses previously cut in the ends of the wrought-iron magnet. Care must be taken in making the pattern for the yoke that the inner edges will not project inward beyond the bore of the pole-pieces. The yoke is fastened to the pole-pieces by screws, as indicated in Fig. 7.

FIG. 7

The rear bearing, 7, is a little peculiar in construction. The box portion is similar to that part of the yoke, but it is cast with a flange, /, i in. from the farthest end of the shell, which is ij ins. long. A collar, n, is fitted to screw onto the outer end of the shell, which is threaded for that purpose. The shell is turned down outside to fit snugly in the hole drilled in the back of the magnet, and when it is inserted in the hole the collar, n, is put on and screwed up tight. This box, like the front one, is bushed to f -in. bore. The drawing shows the flange, /, and collar, n, countersunk in the metal of the magnet; this will not be necessary if the magnet is smoothed up with an emery wheel, as above suggested, the object in countersinking being to provide smooth, true bearing surfaces for the flange and collar.

IO

The armature core, spider, and shaft are shown, partly in crossrsection, by Fig. 9. The core is built up of low carbon steel rings, 4j ins. outside diameter and 2\ ins. inside, not more than 1-32 in. thick; these are assembled on a brass drum, shown by Fig. n, which should be 2§ ins. outside diameter before finishing, so that it may be turned down to exactly fit the inner circle of the armature rings; the wall of the drum is \ in. thick after finishing, and there are four equidistant projecting lugs, /, J in. long, on each end, by which the drum is secured to the spider (see Figs. 9 and 10). The rings forming the core, C (Fig. 9), are compressed and held on the drum, r, by two brass washers, w, w, 3-16 in. thick and 3! ins. outer diameter, which screw onto the ends of the drum. The core, when compressed, is ij ins. long, and has 24 slots 3-16 in. wide and 7-16 in. deep; the washers, w, w, must be set up as tight as the threads will stand.

The spider, s (Figs. 9 and 10), is made of brass, and consists of a hub (f in. diameter, 2 ins. long, and f in. bore) and four arms having Tshaped ends, the wide part or heads of which project beyond the arms and hub at each end, the length of these heads being 2j ins. and their width | in. The heads of the spider arms are turned off to fit very closely inside the drum, r, which is mounted on the spider in such a position as to bring the spider arms in alignment with the lugs, /, of the

ONE-SIXTH HORSE-POWER MOTOR WITH RING ARMATURE ir drum; screws through the spider arms into the lugs hold the drum and spider together.

The shaft, 5, is 8J ins. long; the portion j is ij ins. long and f in. diameter; k is i in. long and 7-16 in. diameter; the part passing through the core is 3 ins. long and f in. in diameter; m is f in. long and 7-16 in.

FIG. 9

FIG. 10

FIG. ii diameter; and p is 3 ins. long and f in. diameter. The spider, s, may be secured to the shaft by a key or a set-screw; the set-screw is sufficient in so small a machine. The commutator (not shown) must not be more than | in. over all, along the shaft; it must have J in. brush surface and 24 segments; other details may be made to suit the will of the builder. The front end of the commutator must be not less than 3-16 in. from the shoulder where j and k join.

The armature is next prepared for winding by removing the drum and core from the spider and insulating the ends and interior of the core and the walls of the slots. Cut four rings of heavy drilling of a size to cover the washers, u>, w, and the ends of the drum, r ; varnish two of them on one side with shellac, and apply them to the ends of the armature body. While these are hardening cut forty- eight strips of drilling ij ins. wide and 2\ ins. long; in each end of each of these cut two slits \ in. long parallel with the sides, and located 15-32 in. from each side of the strip. Varnish these on one side, and when nearly dry fold them into troughs to fit the slots, two troughs to a slot, one within the other; fold them so that the varnish will be on the inside of the trough.

When these are dry varnish the slots and the outsides of the troughs and put the latter in the slots, bending the ends flat against the core and securing them there with a little fresh varnish. Then varnish the ends of the core (two cloth rings being on them), and one side of the two remaining rings of drilling; put these rings on top of the first ones, varnish them on the outside, and put the core in an oven to bake. The armature coils consist of No. 24 double-silk-covered wire, wound 5 turns wide and 14 layers deep. Before winding them four strips of wood 3 ins. long, | in. wide, and J in. thick should be screwed to the inner wall of the brass drum, in line with the lugs, /, so as to preserve the spaces for the four arms of the spider. A double thickness of drilling should also be applied to the interior of the drum to insulate the coils from it. The connections are the 'simple Gramme ring arrangement.

The field winding is necessarily divided into two coils, on account of the rear bearing passing through the magnet. Each coil consists of No. 28 double-cotton-covered wire, wound f in. deep and if ins. long; the two coils are connected in series with each other and in shunt to the brushes. Heads of hard fiber \ in. thick should be used to protect the ends of each coil; one of these is shown by H (Fig. 12), but the width should be f in. instead of j in. as marked.

It is in two pieces, the seams being at the ends, and is cut from J in. sheet fiber. The two halves may be clamped together on the core by means of a small brass wire drawn around the outer edge, laying in a shallow groove, the ends being twisted and cut close. The pole-pieces should be removed before taping and putting on the heads, to facilitate these operations as well as the winding of the coil. One fiber head has a notch, n, half way of its inner long side to enter the field wire. The pole-pieces should, of course, be removed before winding the field coil, and the magnet core should be wrapped with two layers of varnished drilling

ONE-SIXTH HORSE-POWER MOTOR WITH RING ARMATURE where the coils are to go. The entering end of each coil should be remote from the journal, and this means that the magnet must be turned end for end after one coil is wound, or else the two coils must be wound in opposite directions in order that the free ends at the center of the magnet may be connected together. It is advisable to provide a starting switch similar to the one shown diagrammatically by Fig. 13, where F is the field coil; B B the brushes; 5" the starting switch lever; L a 32-candle-power 1 10- volt lamp; M a magnet, and SW a double-pole snap switch.

The motor is intended to be mounted on a wooden base-board 8 ins. x 8 ins., a cleat 3 ins. wide and 7-16 in. thick being put under the pole-pieces so as to clear the field coil. Bolts from beneath, tapped into the tine

FIG. 12

FIG. 13 magnet and countersunk in the under side of the base, should be used to hold the motor on the base. The pulley may be any diameter from i in. to 3 ins. by i in. face, if crowned, or J in. if grooved.

WINDINGS FOR BATTERY CURRENT

For 6- volt battery current the armature should be wound with 12 coils of No. 13 wire, each coil having 16 turns and occupying two (adjacent) slots. The field wire should be No. 18, wound 12 layers deep and 38 turns long in each coil; the two coils containing 912 turns in all. The commutator must have 12 segments and a brush surface j in. wide; copper brushes f x J in. should be used, the contact faces being cut to such a bevel as to present a surface at least \ in. square each. The field winding is to be connected in shunt to the brushes, instead of in series as is usually the practice in battery motor construction. This winding is for 6 volts at the terminals; the current required will depend upon the work done; the machine is capable of standing an armature current of 20 to 25 amperes.

Chapter III One-fourth Horse-power Motor With Drum Armature

FIG. 14 represents the field magnet and Fig. 15 one of the journal yokes of a J horse-power no- volt motor, with a drum armature. The magnet is of the familiar single-coil type. The core is of round machinery steel, 2\ ins. in diameter and 9 ins. long over all. The ends are turned tapering as indicated by dotted lines, to insure intimate contact with the yokes; the taper is from the full diameter to if ins., and begins 2 ins. from each end. The pole-pieces are of cast iron. Fig. 16 gives a plan view and a face view of one pole-piece, from which all the essential dimensions may be obtained. The arms which support the journal yokes are cast solid with the pole-pieces, and their horizontal thickness tapers from J in. at the pole-piece to J in. where the yoke is bolted on.

In fitting the magnet frame together the best procedure is to bore the tapered holes in the lower part of each pole-piece and turn the ends of the magnet core to the same taper, but just a trifle large; then dress each taper down very gradually with a fine file (the core being run in a lathe) until the pole-piece can be pushed on by hand far enough to bring the end of the core within 1-32 in. of the back surface of the cast iron. The pole-pieces and ends of the core should be punch-marked, so as to insure finally mounting each pole-piece on the end to which it was fitted. After dressing down the ends of the core as above described, drill and tap in each end a hole for a J-in. machine screw, the purpose of which will be apparent by glancing at the right-hand end of the magnet in Fig. 14, where C is a four-armed claw or spider with a hole through the center where the arms intersect. The arms are J in. thick, measured at right angles to the bolt, and taper from J in. to J in. thick measured parallel with it. One of these spiders is used at each end, though the drawing shows it at only one end of the machine.