A power-operated digging machine consisting of a lower frame and crawlers, a machinery frame, and a gantry supporting a boom which in turn supports a dipper handle and dipper (see illustration). Dipper sizes range from 1 to 180 yd³ (0.7 to 137 m³). The machines are powered by on-board diesel engines or by electric motors. Diesel-powered machines utilize a series of clutches and brakes that allow the operator to control various motions. Electric motor machines generally have individual motors for each motion, but occasionally clutches and brakes are used allowing one motor to drive two motions.