The armature is wound with three or four layers of wire of the same size.
The commutator is made out of a circular piece of hard wood or fiber, fitted with segments cut out of thin sheet-copper. The segments may be fastened to the core with thick shellac or some melted sealing-wax. The ends may be bound down tightly by wrapping with silk thread.
The brushes are cut out of thin sheet-copper similar to that used for the commutator segments.
The bearings are strips of heavy sheet-brass bent into the shape shown. They are mounted by passing a nail through the holes in the ends and through the holes, A and B, in the field and then riveting the ends over.
Assemble the motor as shown in Figure 255. If desirable, a small pulley may be fitted to the shaft and the motor used to run small mechanical toys. If it is properly constructed, two or three dry cells will furnish sufficient current to run the motor at high speed.
CHAPTER XVII DYNAMOS
There is perhaps no other electrical device entering into the young experimenter’s domain requiring the careful workmanship and tool facilities that the dynamo does. In order to construct a practical working dynamo it would be necessary to have at hand a lathe for turning the castings.
Rather than describe a machine which comparatively few of my readers would be able to build, I have explained below how it is possible to so alter an old telephone magneto that it may be made to serve as a small dynamo. Telephone magnetos, also sometimes called hand generators, are used in many telephone systems to supply the current which rings the telephone bell at the other end. The magneto is placed in a small box on the telephone, only the handle being exposed. In order to make a call the handle is given several brisk turns before raising the receiver. When the handle is turned the moving parts of the generator revolve and produce a current of electricity which goes forth over the line and rings the bell at the other end.
