This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
The motor here described has been constructed and found to give very good results. It is simple to build and the materials required can be easily obtained. The armature core and field, or frame, are made of laminated iron, instead of being cast as is often done by the manufacturers, which is a decided advantage, as certain losses are thereby reduced, and its operation will be improved by this type of construction especially if used on an alternating-current circuit.
The machine will be divided into three main parts, the construction of each of which will be taken up in turn and the method of procedure discussed in detail. These parts are the completed armature, the field and bearings, and the brushes together with suitable terminals and connections.
The armature core is constructed from a number of pieces, having dimensions that correspond to those given in A, Fig. 1. These pieces are cut from thin annealed sheet iron, in sufficient number to make a pile, 3/4 in. high, when placed on top of each other and firmly clamped. It would, no doubt, be best to first lay out one of these pieces very carefully and then cut it out and mark out the other pieces with the first one as a pattern, being careful to file off all the rough edges on each piece.
Now obtain a piece of 1/4-in. brass rod, 3 1/4 in. long, that is to serve as a shaft upon which to mount the armature and commutator. This rod is threaded for a distance of 7/8 in.on one end and 1 7/8 in. on the other. Procure five brass nuts, 1/8 in. in thickness, to fit the threads on the rod. If possible have the ends of the rod centered before the threads are cut, for reasons to be given later. Place one of the nuts on that end of the shaft that is threaded for 7/8in., and in such a position that its inner surface is 3/4 in. from the end of the rod. Solder this nut to the rod when it is in the proper place and remove all extra solder. Drill a 1/4-in. hole in each of the armature stampings and place them on the shaft, clamping them together with three small clamps, one o'n each extension or pole. Then place a second nut on the shaft and draw it up tight against the last stamping placed in position, and solder it to the shaft. Next wind two or three layers of good strong tape around each of the rectangular portions of the armature and then remove the clamps. Make sure that all the edges of the different laminations are perfectly even before applying the tape.
Ill: Details of the Armature Laminations and the Commutator Segments, and the Method of Mounting Armature Core and Commutator
The shaft is then placed between two centers to determine whether the core is approximately balanced and runs true. If the armature core is unbalanced or not true, the trouble should be corrected before proceeding with the remainder of the armature construction. The armature winding is not to be put on the core until the commutator has been constructed and mounted on the shaft.
The commutator consists of three pieces of thin sheet brass similar to that shown at B, Fig 1, mounted on the surface of a cylinder of insulating material, 3/8 in. long and 7/8 in. in diameter. A 1/4-in. hole is drilled lengthwise through the cylinder of insulating material. Bend the pieces of brass around the outside of the cylinder, and turn all the lugs, except the center one, marked C, over at right angles and put a small nail or screw through the holes in the ends of the lugs into the cylinder. These pieces of brass are equally spaced around the cylinder so that all the lugs, not turned down, project in the same direc- tion. Now place a nut on the end of the shaft that extends the greatest distance through the armature, so that its outside surface is 1/2 in. from the surface of the end of the armature core next to it, and solder the nut to the shaft. Place the commutator on the shaft so that the projections on the pieces of brass are toward the armature core and the spaces between the ends of the pieces occupy the position relative to the cores, shown at A, Fig. 2. Another nut is then placed on the shaft and drawn up tight against the cylinder. The proper spacing of the various parts on the shaft of the machine is shown at D, Fig. 1. Another small nut is . placed on the end of the shaft, away from the commutator, so that its outside surface is 1/2 in. from the surface of the end of the armature core.
Ill: Diagram of the Winding on the Armature and Detail of the Field Laminations
The threads on that part of the shaft extending beyond the last nut on each end are now filed off, which can be easily done by placing the shaft between the centers of a lathe and revolving it quite rapidly, the file being applied to the parts that are to be cut down.
Obtain a small quantity of No. 22 gauge single-cotton-covered copper wire and wind four layers on each of the three legs, or poles, of the armature core, insulating the layers from each other and the entire winding from the core by means of paper and shellac.
The three coils are wound in the same direction about their respective cores and each winding is started at the center of the armature with 2 or 3 in. of wire extending out toward the commutator. The outside end of each winding will terminate at the end of the coil toward the center of the armature, if an even number of layers is wound on, and is securely fastened by means of two or three turns of heavy thread. The inside end of one coil is then connected to the outside end of the next one, and so on. These connections can be easily made, and at the same time the proper connections made to the commutator, by cutting the inside end of one coil and the outside end of the next so that they will reach the lug on the nearest segment of the commutator, with about 1/4in. to spare, then removing the insulation from each for about 1/8 in. and soldering them both to the same lug. The arrangement of the winding is shown at A, Fig. 2. Connect all of the coils and segments in this manner, and the armature of the motor is complete.
The field or frame of the machine is made from a number of laminations whose dimensions correspond to those given in B, Fig. 2. As many laminations are used in the construction of the frame as the number of pieces in the armature, if iron of the same thickness is used. Four of the laminations have extensions at their lower corners to correspond to the parts shown by the dotted lines in B, Fig. 2. Place all of these laminations in a pile and clamp them rigidly together, then drill the four holes, indicated by the letters C, D, E and F, with a 3/16-in. drill. Two of the pieces with the extensions on them are placed in the bottom of the pile and the other two on top.
Place a 3/16-in. bolt through each of the lower holes and draw up the nuts on them tight. Procure two pieces of 3/16-in.in. rod, 1 1/2 in. long, and thread each end for a distance of 1/2 in. Get 8 nuts for these rods, about 1/8 in. thick and % in. across the face, if possible. Both sides of these nuts are filed down flat. Put the threaded rods through the two upper hole? in the field frame and place a nut on each end and draw them tight, leaving an equal length of rod protruding from each side.
Obtain two pieces of 1/8-in. brass, % in. wide, one 4 3/4 in. long and the other 5% in. long. Bend these pieces into the forms shown at A, Fig. 3. Drill a 3/16-in. hole in each end of both pieces so that they may be mounted upon the ends of the rods protruding from the field frame. The exact center of the space the armature is to occupy is then marked on each of these pieces, and a hole is drilled in each, having the same diameter as the ends of the armature shaft.
The extensions on the outside laminations are bent over at right angles to the main portion of the frame, thus forming a base upon which the motor may rest. Holes may be drilled in the extensions after they are bent over to be used in mounting the frame upon a wooden base.
Procure about 1/2 lb. of No. 18 gauge single-cotton-covered copper wire and wind it on the lower center portion of the frame until the depth of the winding is about 1/2 in. Be careful to insulate the winding well and, to insure mechanical protection, place a layer of adhesive tape outside. About 4 or 5 in. of wire is allowed at each end for making connections. It is best to have these ends'terminate on the commutator side of the frame.
The brushes for the machine are made from some thin sheet copper or brass, and are shaped and dimensioned approximately as shown at B, Fig. 3. Two pieces of hard rubber, or fiber, 1/2 in. square and 7/8 in. long, serve as mountings for the brushes. These pieces of insulation are mounted in the corners of the armature support, at the commutator end, by means of two small screws in each. Mount the brushes on these pieces so that their free ends bear on the commutator exactly opposite each other. One brush is mounted on the upper end of its support and the other brush on the lower end of its support. This is shown at C, Fig. 3. Two small binding posts are mounted at the same time as the brushes, and are electrically connected to the brushes, thus affording an easy means of making a connection to the armature. The brushes are so mounted as to bear firmly upon the commutator.
Ill: Detail of the Armature supports and the Brushes, and the Manner of Mounting the Brushes
To operate the motor, connect the armature and field windings in series and the combination to a source of electromotive force of several volts. If it is desired to reverse the direction of rotation, reverse the connections of either the armature or field windings, but not both. The motor may be mounted on a neat wooden base and the connections all brought down to a reversing switch, which may also be mounted on the same base as the motor. The speed can be varied by changing the impressed voltage, or by connecting a variable resistance in the armature circuit, such as a wire rheostat.
A small pulley may be made and attached to the armature shaft so that the motor may be used in driving various kinds of toys.