132 Industrial Robotics Fundamentals Copyright Goodheart-Willcox Co., Inc. The rotor speed must be somewhat less than the synchronous speed in order to develop torque. The difference between the synchronous speed and the rotor speed is called slip. The greater the difference between the rotor speed and the synchronous speed, the more torque is produced. As the difference between the rotor speed and the synchronous speed becomes smaller, the percentage of slip decreases as well. (Pictorial) (Schematic) Field windings Armatureat at at Wound armature with brush/split-ring commutator assembly Concentrated field windings To energy source (ac or dc) To energy source (ac or dc) To energy source (ac or dc) To energy source (ac or dc) Armature Goodheart-Willcox Publisher Figure 6-13. Universal motors can operate on either ac or dc energy and are often used to power portable tools. S N Stator windings Squirrel-cage rotor Copper conductors (Schematic) Connecting plate Connecting plates Shaft (Pictorial) Copper conductors Goodheart-Willcox Publisher Figure 6-14. The components of a squirrel cage rotor on an induction motor include copper conductors, connecting plates, and a shaft.