Excavators are heavy construction equipment primarily consisting of a boom, dipper (or stick), bucket, and cab on a rotating platform known as the "house".
The modern excavator's house sits atop an undercarriage with tracks or wheels, being an evolution of the steam shovel (which itself evolved into the power shovel when steam was replaced by diesel and electric power). All excavation-related movement and functions of a hydraulic excavator are accomplished through the use of hydraulic fluid, with hydraulic cylinders and hydraulic motors, which replaced winches, chains, and steel ropes (utilized by dragline excavators). Another principle change was the direction of the digging action, with modern excavators pulling their buckets toward them like a dragline rather than pushing them away to fill them the way the first powered shovels did.
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