Open main menu

Page:Popular Science Monthly Volume 56.djvu/425

This page has been validated.
411
WHAT MAKES THE TROLLEY CAR GO.

the bottom of the car, where it enters the wire d d at the point c. This wire d d, as will be seen, runs in both directions, and ends in the stands C C. These latter are the controlling switches, and are provided with a handle h, by means of which the current is turned on or off from the motors, and is directed through them in such a way as to make the car run in whichever direction may be desired. From the controllers C C several wires are run under the car, as shown at e e e. These wires are generally bunched into one or two cables, but they are kept separate from each other by means of strong insulating coverings. Four wires lead into each motor, and three or four into each of the boxes marked G G. If the motors were required to run in one direction only, then two wires would be sufficient to convey the current to them; but as they have to run in either direction, at least three wires are necessary, but in almost every case four are used, as the results obtained thereby are more satisfactory. The boxes G G are called rheostats, and are simply devices through which the current is run so as to reduce the speed of the car, and also for the purpose of graduating the strength of the current that passes through the motors in the act of starting. These rheostats are very seldom in use when the car is in motion, because it is a waste of power to pass the current through them. After the current has passed through the motors it enters the ironwork, and thus gets into the car wheels and finally to the track.

The lines drawn in Fig. 18 to indicate the position of the wires in the car do not show their actual position, but only the general direction they follow. From the trolley base to the first hood switch the wire, as a rule, is run along the car roof on one side of the ventilator, and the wire leading from the first to the second hood switch occupies a corresponding position on the opposite side of the roof. From the last hood switch, h, the wire is run down one corner of the car body, being either within the car body, or, if not, so covered by moldings as to not be reached by the hands of passengers. The wires d and e are generally run under the car, and are firmly secured to it by means of suitable fastenings.

The controlling switches C C are provided with one and sometimes two handles, one of which is used to regulate the speed of the car and stop and start it, while the other is for the purpose of reversing the direction in which it runs. The handle h is for the purpose of regulating the speed, and by means of k the direction of motion is changed. Before h is moved from the inactive position k is turned so that the car may run either forward or backward, as may be desired; then, when h is moved, the car will start, and by varying the position of h the speed can be changed. If it is de-