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.
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Fig.4
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
