Successful operation and construction that is feasible, yet of a reasonable standard of workmanship, are the essentials of the locomotive truck and cab described as the second feature of the locomotive and track system under consideration. The materials suggested are those found to be satisfactory, but substitutes may be used if caution is observed. The completed locomotive is shown in [Figs. 1 and 2]. The outward aspect only is presented, and, for the sake of clearness, the portions of the motor and driving rigging attached to it, that project below the cab, are omitted, These parts are shown assembled in [Fig. 12], and in detail in the succeeding sketches.
The locomotive, apart from the motor, consists of two main portions, the truck and the cab. Consideration will be given first to the building of the truck and the fitting of the motor into it. The mechanical and operative features are to be completed before beginning work on the cab, which is merely a hood fixed into place with screws, set into the wooden cab base.
Begin the construction with the wheels, shown in [Fig. 3]. Make the axles of ¹⁄₈-in. round steel rod, cut 3³⁄₁₆ in. long.
Turn four wheels of ³⁄₈-in. brass. Drill a ¹⁄₈-in. hole in two of them so that they may be forced on the slightly tapered ends of the axle. Drill a ¹⁄₄-in. hole in each of the other wheels, and solder a collar, A, [Fig. 3], on the inside surfaces of them. Two fiber bushings, B, should be provided to fit in the ¹⁄₄-in. openings in the wheels and to fit tightly on the ends of the axles. This insulates the wheels on one side of the truck from those on the other. If the rails forming the track are insulated from each other, the current supplied to the motor may pass in on one rail to the two insulated wheels, then to a brush, which bears on the brass collar A, through the windings of the motor, through the reversing switch to the other set of wheels, and back to the source of energy over the other rail, as shown in [Fig. 15].
The wheels of the truck should fit on the axles tightly, since no means other than the friction will be employed in holding them in position. If the ends of the axles are tapered slightly, the wheels may be forced into place and will stay firmly. Do not force them on until the truck is finally assembled.
The truck frame should be constructed next, and its details are shown in [Figs. 4 and 5]. Make two sidepieces of ¹⁄₁₆-in. brass, 9³⁄₄ in. long and 1⁵⁄₈ in. wide, cutting out portions, as shown, in order to reduce the weight. This also gives the appearance of leaf springs.
The two rectangular openings are to accommodate the axle bearings. They should be cut to precise dimensions, and their edges should be squared off. Extensions, ¹⁄₁₆ in. wide, are provided at the middle of the upper edges of each of these openings. They are to hold the upper end of the coil springs, which are to rest in the holes cut into the bearings, as shown at G, [Fig. 7], and also in assembled form, [Fig. 6].
Next drill four ¹⁄₈-in. holes in each of the sidepieces, as indicated at the letters H₁ to H₄, [Fig. 5]. For the cross supports use four pieces of brass rod, ¹⁄₄ in. square, and square off the ends to a length of 2³⁄₄ in. Drill holes in the center of the ends and tap them for ¹⁄₈-in. machine screws. Join the side and crosspieces as shown in [Fig. 4]. Two fiber washers about ¹⁄₁₆ in. thick should be placed on each axle at E and F, to hold the wheels from contact with the sidepieces.
Details of a bearing for the axles are shown in [Fig. 7]. The hole G carries the lower end of the coil spring, and the hole J is the bearing socket for the axle. Four spiral springs, having an outside diameter of ¹⁄₈ in. and a length of ¹⁄₂ in. when extended, should be provided. The extensions on the sides of the bearings fit against the inner faces of the sides of the truck. They hold the bearings in position and prevent them from falling out.
The base of the cab is made of wood, dimensioned as in [Fig. 10]. The center of the piece is cut away so as to provide a space for the motor, which extends above the upper edge of the truck, as shown in [Fig. 12]. This block is fastened in place by four screws through the upper crosspieces at the ends of the truck. The base should be made and fitted into place temporarily so as to be available in observing how the motor and its fittings are placed in relation to it. For convenience in assembling the parts of the truck and setting the motor, it may be removed readily.