54 



ELEMENTS OF ELECTRICAL ENGINEERING. 



pass from the armature coils to the commutator bars. The 

 brushes are carried by two insulated metal studs fixed to an arm 

 which is supported upon the projecting end of one of the bearings. 

 This arm may be turned about the axis of the armature at will, 

 and clamped so as to hold the brushes in any desired position. 



Fig. 41. 



The brushes of direct-current dynamos are always carried upon 

 a supporting arm or frame which may be turned about the axis 

 of the armature at will. This adjustable brush support is called 

 a rocker-arm or rocker-frame. 



Fig. 42 is a general view of a multipolar dynamo manufac- 

 tured by the Fort Wayne Electric Works. The field yoke, that 

 is, the external ring of the field magnet, is cast in two parts which 

 are bolted together, and the upper part of the field may be lifted 

 off when it is desired to remove the armature. Fig. 43 is a 

 view of the field structure and base, with the armature and all 

 field windings removed. One of the laminated structures which 

 constitutes a combined field magnet core and pole piece, is shown 

 in Fig. 44. These pole pieces are set into the mould and cast- 

 welded to the field ring. An enlarged area of pole face is ob- 

 tained by the use of an open frame of cast iron, shown in Fig. 



