Assumptions and a mathematical description of a system of fixed axes d-q of a shunt asynchronous commutator motor have been presented. Two constructional modifications met in practice of this motor are analyzed. The relation between parameters of the commutator winding and angular distance of brushes have been determined. In order to simplify the analysis and expression which determines the electromagnetic moment it was assumed that the stator and rotor of the motor are mutually displaced. Voltage equations have been formulated for an arbitrary shift angle of axis of commutator winding and angular distance of brushes.