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.
By A. G. McCLURE
An exceedingly simple and inexpensive motor that may be used in operating small toys can be constructed as follows: First procure a good permanent magnet, about 5 in. long and about 1 1/2 in. between the inside edges at the open end. This magnet should be at least 1/2 in. thick, and if it cannot be had in one piece, two or more may be placed side by side, like poles being placed together. The writer was unable to procure ready-made magnets, so one was formed and magnetized. Obtain a piece of tungsten or some other good-grade steel, 1/2 in. by 1/2in., and about 11 in. long. Bend this piece into the form of a U, with the inner edges 1% in. apart. Square off both ends and drill two small holes in the outside surface of each end, at AA, about % in. from the end. Tap these holes for small machine screws. Drill the hole B with a small drill, about 1 1/6 in., in the center of the lower portion of the U and ream it out. The piece should now be clamped with a good pair of blacksmith's tongs, - a block of iron being placed between the ends to keep the pressure of the tongs from drawing them together - heated to a cherry red and then plunged into a bath of oil. It can then be magnetized by placing it in contact with a permanent magnet.
Next obtain a piece of 1/8- in.brass, about 1/2in. wide and 5 1/2 in. long. Drill two holes in each end of the piece to match those drilled in the ends of the magnet, also one in the center, and tap it for a 1/8-in. machine screw. Now bend this piece into the form shown. Provide a machine screw, S, for the hole C and drill a small tapered hole in the end of the screw.
Obtain a small quantity of soft sheet iron and cut a sufficient number of pieces similar to that shown at D to make a pile 1/2 in. high. Cut two pieces of the same size from some thin sheet brass. Now place all of these pieces in a pile, the brass pieces being on the outside, and clamp them securely, then drill the two small holes, E and F. Place two small copper rivets in these holes and rivet the heads down before removing the clamp. Drill a 1/8-in. hole, G, through this piece, the armature, for the shaft to pass through. Procure a piece of %-in. steel rod, about 6 in. long. Sharpen one end so that it will enter the hole B, then cut the other end off and sharpen it so that it will enter the opening made in the end of the screw S. The armature may now be soldered to this shaft, its left-hand surface being flush with the ends of the magnet.
Ill: Detail of Armature Laminations, and Completed Parts Assembled, but without Armature Windings
A small commutator, H, should now be made as follows: Obtain a piece of thin brass tubing about % in. in diameter. Turn down a piece of hard rubber so that the tube will fit tightly on it. Drill a hole in this piece of rubber of such a size that it will have to be forced on the steel shaft. Saw two longitudinal slots in the brass tube diametrically opposite each other and then bind these two pieces in place on the piece of rubber with some heavy linen thread wrapped around each end. The armature is now ready to wind. Get a small quantity of No. 22 gauge cotton-covered wire, solder one end to one of the segments of the commutator, then wind one end of the armature full and cross over and wind the other end full, soldering the end of the wire to the second commutator segment. Make sure to wind both ends of the armature in the same direction so the current in both parts of the winding produces magnetizing effects in the same direction. Insulate the winding from the core and the different layers from each other with a good quality of thin writing paper.
Two small brushes should now be made from some thin spring brass and mounted on the brass piece as shown. These brushes should be insulated from the piece of brass and two small binding posts should be provided for making connections to them. The position of the commutator and brushes should be such that the brushes move from one segment to the other when the ends of the armature are directly in line with the ends of the permanent magnet.
A small pulley should be mounted upon the shaft to be used in transmitting the power. The whole device may be mounted in a horizontal position on a wooden base as shown, and the motor is complete.