THE CONTINUOUS CURRENT MOTOR 



169 



Effect of Forward Brush Shift. If the brushes are 

 shifted forward to the plane A" E" the motor will slow 

 down with an increase of load. This is due to three effects. 

 The IR a drop increases with the load and so slows the 



Fia. 103. E.M.Fs. in Conductors of a Commutating-pole Motor. 



motor down as shown before; the armature reaction in a 

 motor tends to magnetize the main field when the brushes 

 have a forward shift and so increases the counter e.m.f., 

 thus causing a speed decrease; when the brushes are in 

 the plane A" B" it is seen that the inductors marked M 



