from Real Electric Toy-Making for Boys
163.
Engines and Motors. This toy electric engine, if properly made,
will run well on two or three dry cells. While machines of this sort are
not so efficient as regular electric motors, they bring out several elementary
principles that are used upon the more complicated electrical machines
and instruments. It will be valuable to any boy to make simple machines
of this sort.
164. Parts. Figs. 61, 62, 63. Two solenoids; base; dowels; spools; brass screw-eyes; pasteboard; thin sheet copper or tin; soft iron rivets.
165. Details of Construction. (A) Make two solenoids, A, B, as fully explained in No. 39, and mount them on special spools, C, D, which are made as described in § 150A.
(B) Make a wooden base 3 3/4 x 6 1/2 in. This may be 7/8 in. thick or it may be made of thin wood and mounted upon legs, as shown in Fig. 61.
(C)
Draw a line lengthwise along the center-line of the base to serve as a
guide for locating the spools. Nail spools C and D upon the line at the
ends of the base, and next to these nail two half-spools, E, F. Cut two
6 in. lengths of 5/16 in. dowels, G, H, and drive these into spools E
and F. Drill a hole in the upper ends of G and H, and into these screw
small brass screw-eyes, I, J. (D) The revolving part consists of a shaft,
K, a flywheel, L, revolving contacts, M, Z, axles, N, and wires.
(E) The shaft is made of a 3-in. length of 5/16-in. dowel. This extends through the contacts and fly-wheel, which are placed on the shaft as shown.
(F) The fly-wheel is made as shown in detail in Fig. 62. It consists of three or four thicknesses of stiff pasteboard cut 3 1/4 in. in diameter (see chapter on "Pulleys and Winding-Drums" for methods of handling pasteboard). Two small stove-bolts, O, with iron washers, are put through holes made on opposite sides of the wheel and one-half inch from the circumference. These are to give weight to the wheel. They are not absolutely necessary, but they make a heavier wheel. Make a 5/16 in. hole through the center of the wheel and nail it to the face of spool P.
(G) The revolving contacts, M, Z, are shown in detail in Fig. 62. Bore out spool P to take the 5/16-in. shaft, and saw off one flange. Divide the end of the spool into six equal parts, as indicated by the lines, and with small nails fasten curved pieces of thin sheet copper to it. Make each copper contact 3/4 in. long, and wide enough to cover exactly one-third of the surface of the spool, as seen at the end. No. 18 copper wires Q and R, lead from the two contactors to the axles, around which they are twisted to make good connections. The nails which pass through the contacts will hold spool P to the shaft. Wire R may be passed through a hole made in the pasteboard.
(H) The axles, N, N, are made of brass screw-eyes, the eyes of which have been straightened out. These eyes should be at least 3/8 in. inside diameter. This will give a total movement of 1/2 in. to the rivets if properly bent. With good pliers you will have no trouble in getting them into the form shown. Drill holes in the ends of shaft K, being careful to have them straight, then screw in N N so that they will not only be exactly opposite each other but also in line with the centers of the contact, as shown at N, Fig. 62.
(I) Wires S S are twisted around screw-eyes I J, and lead to one wire of each solenoid. The other terminals of the solenoids pass to a common binding-post or screw, T. A long No. 18 copper wire, U, leads the current from the cells to the contact.
Fig. 63 shows
how to bend U at the bottom, so as to adjust its pressure against the
contacts. A short piece, only, of the vertical wire is shown. By sliding
the bent portion one way or the other the pressure can be regulated.
(J) The iron rivets, V, W, are supported by wire loops, as explained in § 160 D, and through these, strings X X are passed. The upper ends of these strings are tied to small screw-eyes, Y, Y, which are slid upon the axles, or to wire loops. Adjust the lengths of the strings so that the lower ends of the rivets will nearly reach the bottom of the solenoids when they are at the lowest point, as shown for V.
(K) Connect two cells in series with the two binding posts. The wire, U, must touch one of the contactors in order to have the current pass.
166. Brushes and Commutators. Wire U, which admits current to the revolving contacts, M, Z, is called a brush. It scrapes against the contacts as they revolve. We may call these combined contacts a simple form of commutator, which automatically turns the current on and off.
167. Action of Electric Engine. Suppose that the current enters brush U and goes through contact Z, wires R and S to solenoid B and back to the battery by binding-post T. This will magnetize solenoid B and draw in the core. As no current can enter contact M at the same time that it enters Z, there will be no magnetism in solenoid A at the time core W is being drawn down. When W gets to the proper position, U leaves contact Z and presses against the spool until the shaft turns a little farther. In the meantime core V has been lifted. Contact M now gets current and V is drawn down.
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