CHAPTER XIX.
ELECTRIC MOTORS.
249. An Electric Motor is really a machine. If it be supplied with a proper current of electricity, its armature will revolve; and, if a pulley or wheel be fastened to the revolving shaft, a belt can be attached, and the motor made to do work. There are many kinds of motors, and many simple experiments which aid in understanding them. All that can be done here, however, is to show how to make simple motors. (See text-book for experiments.)
250. Electric Motor. Fig. 116, 117. Fig. 116 shows a plan or top view, and Fig. 117 shows a side view, with a part of the apparatus removed, for clearness.
The base, B, is 5 × 4 × ⅞ in. The upright, U, is 3½ × 1½ × ½ in., and is nailed or screwed to B. The binding-posts, X and Y are like [App. 46]. 4 is a screw binding-post.
251. The Field-Magnets, as the large electro-magnets on a motor are called, are made of 5⁄16 machine-bolts, 2½ in. long. The washers are 1½ in. apart inside. ([See App. 88] for full directions.) The bolt cores are 2 in. apart, center to center. ([See App. 89].) The tin yoke, D, is made like [App. 71], and it is fastened to the base, like [App. 90]. The hole for the screw, however, is made a little to one side of the center, so that a dent can be made at the center for the bottom of the shaft, 8, to turn in. Make the dent with a center punch. The yoke is fastened to B, so that one edge of it is 1½ in. from the back edge of B. (Fig. 116).
252. The Armature, A, is made of 6 or 8 thicknesses of tin, 2½ in. long and ¾ wide. ([See App. 71].) In its center is punched or drilled a ¼ in. hole, so that it can be slipped onto the ¼ in. "sink-bolt," 8. If you have taps you can make the hole a little smaller than ¼ in., and thread it so that it will screw onto 8. A must be heavy enough to revolve a few times when once started. It is pinched between two nuts, 9 and 11, so that it just clears the poles when it turns. ([See App. 145] for another form of armature.)