Page:Motors and motor-driving (1902).djvu/315

Rh of arranging all the wire in a single winding, we may distribute it over the surface of a soft iron cylinder, connecting it up to the sections of the commutator. This forms a drum armature, and is used in the great majority of electric motors employed on electromobiles. Such drum armatures of course differ in proportions, but the general arrangement is the same.



Figs. 2, 5, and 6 illustrate the three main types of the two-pole electric motors. Fig. 2 shows, as already explained, a two-pole separately excited motor. This may be looked upon as a motor in which the magnet is rendered magnetic by a current from a separate battery (a few accumulator cells usually sufficing for this purpose). To all intents and purposes it may be regarded as if the separately excited