[Illustration: FIG. 16.--RAILWAY MOTOR WITH CASING OPEN, SHOWING ARMATURE IN LOWER HALF.]
As will be noticed in Fig. 16, the motor casing is made so as to open along the central line, and the lower half is secured to the top by means of hinges, _g g_, Fig. 15, and also by a number of bolts, which are not so clearly shown. The gear wheels are also located within a casing, which (Fig. 16) is made so as to be readily opened whenever it becomes necessary. All the vital parts of the machine are entirely covered, and are not easily injured by mud or water.
The construction of the armature and commutator is well illustrated in Fig. 17, which shows this part of the machine by itself. The armature is marked _A_, the shaft _B_, and the commutator _C_. In the diagrams, Figs. 9, 10, 11, and 12, the wire coils are represented as wound upon the surface of the armature core, but, from Fig. 17, it will be noticed that they are located in grooves. A railway motor armature core, when seen without the wire coils, looks very much like a wide-faced cog wheel with extra long teeth, not very well shaped for gear teeth. In Fig. 17 the ends of the teeth are marked _D_, and the grooves within which the wire is wound are marked _E_. The coils are not wound so that their sides are on diametrically opposite sides of the armature core, but so that they may be one quarter of the circumference apart, and, as will be noticed, the wires are arranged so as to fit neatly into each other at the ends of the armature core. The bands marked _F F F F_ are provided for the purpose of holding the wire coils within the grooves. The flanges _H_ and _I_ are simply shields to prevent oil, grease, or even water, if it should pass through the bearings, from being thrown upon the commutator or armature. The pinion through which the armature imparts motion to the car-wheel axle is not shown in Fig. 17, but it is mounted upon the taper end of the shaft.
[Illustration: FIG. 17.--ARMATURE OF ELECTRIC RAILWAY MOTOR.]
An electric railway motor is a machine that is characterized by extreme simplicity (there being only one moving part), compactness, and great strength. In addition, as none of the working parts is exposed it can not be injured, no matter how much mud may accumulate upon it. One of the reasons why the electric railway motor has met with such unparalleled success is that it is a machine that can withstand the roughest kind of usage without being damaged thereby. Another reason is that an electric motor can, if called upon, develop an amount of power two or three times greater than its full-rated capacity without injury, providing the strain is not maintained too long. A steam engine or any other type of motor that has ever been used for railway propulsion if loaded beyond its capacity will come to a standstill--that is, it will be stalled--but an electric motor can not be stalled with any strain that is likely to be placed upon it. If the load is increased the motor will run slower and the current will become greater, thus increasing the pull, but the armature will continue to rotate until the current becomes so great as to burn out the insulation. A railway motor calculated to work up to twenty-five-horse power will have to develop on an average about six-or seven-horse power, but if the car runs off the track on a steep grade, and has such a heavy load that the motor is called upon to develop one-hundred-horse power for a few seconds, the machine will be equal to the occasion. This result a steam, gas, or any other type of engine can not accomplish, and it is this fact as much as anything else that has given the electric motor the control of the street-railway field.