The equations and circle diagrams of the schrage motor

Reliable equations of performance are derived for the Schrage motor by the use of tensor calculus. From these equations the centres and radii of the circle diagrams are established. Each circle is related to a certain brush separation and a certain brush shift, which control respectively the speed and the power factor of the motor. The circle diagrams are often totally unreliable owing chiefly to wide changes in secondary resistance, a large proportion of which is brush contact resistance. The effect of this is investigated and supplemented by the calculation of two examples: in one of these the secondary resistance can be considered constant and circle diagrams can be calculated; in the other the secondary resistance is variable and the equations of performance have to be used.