The motor is of the series type, having its field and armature terminals connected to the source of electrical energy through a special reversing switch. By this means the rotation of the armature may be reversed to make the locomotive travel forward or backward. The armature and field are constructed of sheet-iron stampings, riveted together.
The detailed construction of the armature and its dimensions are shown in [Fig. 2]. The shaft upon which the armature core and commutator are to be rigidly mounted is made of a piece of steel rod, ⁷⁄₃₂ in. in diameter. A portion of this rod, 2¹⁄₄ in. long, is threaded with a fine thread, and two small brass, or iron, nuts are provided to fit it. The ends of the rod are turned down to a diameter of ¹⁄₈ in. for a distance of ¹⁄₈ in. These are to fit in the bearings that are to be made later.
Cut from thin sheet iron a sufficient number of disks, 1¹⁄₈ in. in diameter, to make a pile exactly ⁵⁄₈ in. thick when they are securely clamped together. Drill a hole in the center of each of these disks, of such a size that they will slip on the shaft snugly. Remove the rough edges from the disks and see that they are flat. Cut two disks of the same size, from a piece of ¹⁄₁₆-in spring brass, and drill a hole in the center of each, so that they will slip on the shaft. Place all these disks on the shaft, with the brass ones on the outside, and draw them up tightly with the nuts provided. Be sure to get the laminated core in the proper position on the shaft by observing the dimensions given in the illustration, [Fig. 2].
Fig. 1
Side View of a Locomotive Designed to be Operated with Either End Forward
After the disks have been fastened, clamp the shaft in the chuck of a lathe and turn down the edges of all the disks so that they form a smooth cylinder, 1¹⁄₁₆ in. in diameter. Draw a circle on the side of one of the brass disks, ³⁄₃₂ in. from the edge, while the shaft is held in the chuck. Divide this circle into eight equal parts and make a center-punch mark at each division. Drill eight holes through the core lengthwise with a ³⁄₁₆-in. drill. If the centers of the holes have been properly located, all the metal on the outside will be cut away, as shown in the end view, at the right in [Fig. 2]. The width of the gaps, F, G, H, etc., thus formed, should be about ¹⁄₁₆ in. Smooth off all the edges with a fine file after the holes are drilled.
A cross-sectional view of the commutator is shown at the extreme left, [Fig. 2]. It is constructed as follows: Take a rod of copper or brass, ⁷⁄₈ in. diameter, and 1¹⁄₄ in. long; clamp one end in the chuck of a lathe. Turn the other end down to a diameter of ³⁄₄ in., and drill a ¹⁄₂-in. hole through it at the center. Cut away the metal from the end to form a disklike recess.
Cut off a disk, ⁵⁄₁₆ in. thick, measuring from the finished end, from the piece of stock. Place this disk in a chuck, with the unfinished end exposed, and cut away the metal in a dish form, as shown at B. Cut small slots, into which the ends of the wires used in winding are to be soldered, as shown at 1, 2, 3, etc., in the right-hand view of [Fig. 2]. Obtain two brass nuts, about ¹⁄₄ in. in thickness, and turn their edges down so that they correspond in form to those shown at C and D. Divide the disk ring, just made, into eight equal parts, by lines drawn across it through the center. Cut eight slots at these points, in the rim of the disk. These cuts should be through the rim. Fill each of the slots with a piece of mica insulation.
Fig. 2