<P> The squirrel - cage rotor consists of laminated steel in the core with evenly spaced bars of copper or aluminum placed axially around the periphery, permanently shorted at the ends by the end rings . This simple and rugged construction makes it the favorite for most applications . The assembly has a twist: the bars are slanted, or skewed, to reduce magnetic hum and slot harmonics and to reduce the tendency of locking . Housed in the stator, the rotor and stator teeth can lock when they are in equal number and the magnets position themselves equally apart, opposing rotation in both directions . Bearings at each end mount the rotor in its housing, with one end of the shaft protruding to allow the attachment of the load . In some motors, there is an extension at the non-driving end for speed sensors or other electronic controls . The generated torque forces motion through the rotor to the load . </P> <P> The rotor is a cylindrical core made of steel lamination with slots to hold the wires for its 3 - phase windings which are evenly spaced at 120 electrical degrees apart and connected in a' Y' configuration . The rotor winding terminals are brought out and attached to the three slips rings with brushes, on the shaft of the rotor . Brushes on the slip rings allow for external three - phase resistors to be connected in series to the rotor windings for providing speed control . The external resistances become a part of the rotor circuit to produce a large torque when starting the motor . As the motor speeds up, the resistances can be reduced to zero . </P> <P> The rotor is a large magnet with poles constructed of steel lamination projecting out of the rotor's core . The poles are supplied by direct current or magnetized by permanent magnets . The armature with a three - phase winding is attached to three slip rings with brushes riding on them and mounted on the shaft . The field winding is wound on the rotor which produces the magnetic field and the armature winding is on the stator where voltage is induced . Direct current (DC), from an external exciter or from a diode bridge mounted on the rotor shaft, produces a magnetic field and energizes the rotating field windings and alternating current energizes the armature windings simultaneously . </P> <P> The cylindrical shaped rotor is made of a solid steel shaft with slots running along the outside length of the cylinder for holding the field windings of the rotor which are laminated copper bars inserted into the slots and is secured by wedges . The slots are insulated from the windings and are held at the end of the rotor by slip rings . An external direct current (DC) source is connected to the concentrically mounted slip rings with brushes running along the rings . The brushes make electrical contact with the rotating slip rings . DC current is also supplied through brushless excitation from a rectifier mounted on the machine shaft that converts alternating current to direct current . </P>

Difference between cylindrical rotor and salient pole rotor