These new coils are connected to the commutator in the same way as the old ones were before being removed, just as if the motor was to be used in the ordinary manner.
A two-point switch will be necessary in order to complete the arrangements. The connections should be made as in Figure 49. The switch should be thrown to the right, on contact A, for starting so that the current flows through the field and through the extra coils on the armature in the ordinary way. As soon as the motor has reached its speed, throw the switch to the left so that the current flows through the field only and the motor will continue to run by induction.
HOW TO BUILD AN ELECTRIC ENGINE
An electric engine is really a form of electric motor but differs from the most common form of the latter in that the armature, instead of revolving, oscillates back and forth, like the piston of a steam or gasoline engine. Electric engines are not as efficient as electric motors from the standpoint of the amount of power delivered in proportion to the current used, but they make very interesting models and the young experimenter will derive fully as much pleasure in constructing one as from the construction of an electric motor.
FIG. 50.—The completed Engine.
Various forms of electric engines were made before the first practical electric motor was invented. They amounted to little more than curiosities however, and could only be used where the expense of electric current was not to be regarded.
The engine illustrated in Figure 50 is of the double action type. It is provided with two electromagnets arranged so that one pulls the armature forward and the other pulls it back. The motion of the armature is transmitted to the shaft by means of a connecting rod and crank. It is very simple to build and the design is such that it will operate equally well whether it is made large or small. If you do not happen to have all the necessary materials to build an engine according to the dimensions shown in the drawings, you can make it just one-half that size, and it will work equally well although it will, of course, not give as much power.
FIG. 51.—The Base.