Fig. 242.—A Simple Electric Motor which may be made in Fifteen Minutes.
When this is finished, fasten the wire securely to the cork by binding it with thread.
Bend the two free ends (the starting and the finishing end) down at right angles and parallel to the shaft so as to form two commutator sections as shown in the upper left hand corner of Figure 242. Cut them off so that they only project about three-eighths of an inch. Bare the ends of the wire and clean them with a piece of fine emery paper or sandpaper.
The bearings are made by driving two pins into a couple of corks so that the pins cross each other as shown in the upper right-hand corner of Figure 242.
They must not be at too sharp an angle, or when the armature is placed in position, the friction of the shaft will be so great that it may not revolve.
The motor is assembled by placing the armature in the bearings and then mounting two bar magnets on either side of the armature. The magnets may be laid on small blocks of wood and should be so close to the armature that the latter just clears when it is spun around by hand. The north pole of one magnet should be next to the armature and the south pole of the other, opposite.
Connect two wires about one foot long and No. 26 B. & S. gauge in diameter to a dry cell. Bare the ends of the wires for about an inch and one half.
Take the ends of the two wires between the forefinger and thumb and bend them out, so that when the armature is revolved they can be made just to touch the ends of the wire on the armature, or the "commutator sections," as they are marked in the drawing.
Give the armature a twist so as to start it spinning, and hold the long wires in the hand so that they make contact with the commutator as it revolves.
Very light pressure should be used. If you press too hard, you will prevent the armature from revolving, while, on the other hand, if you do not press hard enough, the wires will not make good contact.