The three main sections of an excavator are the undercarriage, the house and the arm. The undercarriage includes tracks, track frame, and final drives, which have a hydraulic motor and gearing providing the drive to the individual tracks. Undercarriage can also have blade similar to that of a bulldozer. The house includes the operator cab, counterweight, engine, fuel and hydraulic oil tanks. The house attaches to the undercarriage by way of a center pin. High pressure oil is supplied to the tracks' hydraulic motors through a hydraulic swivel at the axis of the pin, allowing the machine to slew 360° unhindered and thus provides the left-and-right movement. The arm provides the up-and-down and closer-and-further (or digging movement) movements. Arm consist typically of boom, stick and bucket with three joints between them and the house.
The boom attaches to the house and provides the up-and-down movement. It can be one of several different configurations:
Most common are mono booms; these have no movement apart from straight up and down.
Some others have a knuckle boom which can also move left and right in line with the machine.