FIG. 46.—The Bearings.
The left hand brush bears against the upper side of the commutator and is connected to a second binding post on the base of the motor. This makes it a "series" motor, that is, the armature and the field are connected in series.
FIG. 47.—Brush and Supporting Block.
The motor is now ready to run. Put a drop of oil on each bearing and make certain that the curved portion of the brushes bear firmly against the centre of the commutator on opposite sides. The armature having three poles, should start without assistance and run at high speed as soon as the current-is applied. Two cells of dry or other battery should be sufficient. The motor may be fitted with a small pulley so that its power may be utilized for driving small models.
HOW TO MAKE AN EXPERIMENTAL INDUCTION MOTOR.
A motor having a three-pole armature will run on alternating current as well as on direct current and can be operated on the 110 volt A. C. current in series with a suitable resistance. The average experimenter is probably aware of this but did you know that it can also be operated on alternating current as an induction motor and that it will then run without brushes and without current being led into the armature?
In order to make an induction motor out of an ordinary three-pole battery motor such as that shown in Figure 48 it is merely necessary to remove the brushes and bind a piece of bare copper wire around the commutator so that it short circuits the segments.
The alternating current should be led into the field coil. A step down transformer will prove very useful for producing a low voltage alternating current which may be connected directly to the field coil. If a transformer is not available, the 110 v. alternating current can be used, provided that a proper resistance such as a lamp bank, be placed in series with the motor.