Switches are a set of copper bars insulated from each other and arranged on a circular surface fixed to the shaft. https://www.mrosupply.com/popular_products/34-hp-56c-motors/ The coils of the armature winding are connected in series, forming a closed winding, the terminals of these coils being soldered to the bars, where only two coils of the winding are indicated. As the coils rotate integrally with the rotor, stationary brushes, in relation to the commutator fixed in the housing and pressed by springs against the bars, make the electrical connection between the external and internal terminals of the armature.
The rotors are cylindrical in shape and house the winding of armature made by coils distributed in grooves. On the rotor shaft and externally to the cylindrical structure of the armature the switch is fixed. It is in the armature winding that the electric voltage associated with the conversion is induced. The term armature is used for circuits that have the highest electrical power of rotating electric machines. In the synchronous machines, which like to the continuous ones have two circuits with distinct and well defined functions, the field circuit is in the rotor and the one of the armature in the stator; in the group of induction machines there is no difference between the field and the armature.