Put a drop of oil on the bearings, make sure that the brushes bear firmly but not tightly against the commutator, connect the battery and your motor is ready to run. It will spin at a high rate of speed.
FIG. 19.—The completed Motor.
SIMPLEX MOTOR WITH THREE-POLE ARMATURE.
The form of "Simplex" motor which has just been described has only one drawback which prevents it from being a first class motor in every respect, namely, the armature has only two poles and the motor is therefore not self-starting, but must be given a twist with the fingers in order to start it rotating. A Two-pole armature is the easiest for the young experimenter to make and that is the reason that it has been described first.
All large power motors are provided with armatures having a large number of poles so as to be self-starting and to give as steady a pull as possible.
The Armature—The method of making a three-pole armature is practically the same as that of making one having only two poles. Three strips of tin, one-half an inch by one and one-half inches are necessary. They are purposely made a little longer than is actually required in order to form the armature and are cut to length after the finish of the bending operations.
FIG. 20.—Details of the Three-pole Armature.
Mark a line carefully across the center of each strip. Then bend them into the shape shown in Figure 20, taking care to keep the shape symmetrical so that all three pieces are exactly alike. The bend in the center which must fit over the shaft is most easily made by bending the strips over a knitting-needle and then bending them back the required amount.