Plain-rotor rotors are differentiated by having a uniform cylindrical shape and a package of non-segmented, single-piece or laser-cut plates mounted on the shaft generally https://www.mrosupply.com/v-belts/v-belts/b-section/178346_b128_gates-rubber/ through ribs. Due to this rotor construction, the air gap is generally constant throughout the rotor circumference, with possible paths for magnetic flux also by the interpolation regions, where plates also exist, which provide greater flux dispersion.
The poles are formed by grouping the plates of the package and therefore are part of the package of plates of the rotor and are not detachable. The field coils are made of insulated copper wires and housed in slots in the sheet pack, with configuration of coils distributed around the poles at the periphery of the rotor. The coil heads are secured through a bandage or shaped steel sleeve on the coils. The cage of this type of rotor is also distributed symmetrically. This rotor configuration has high symmetry, masses evenly distributed over the entire length of the rotor, making it cylindrical, compact and reinforced. Because of these characteristics the synchronous motors with plain poles rotor are more commonly used in machines of high rotation.