Arm (Stick)

The arm, also known as the stick or dipper, is a pivotal structural member in excavator work equipment assemblies. It functions as the intermediate linkage between the boom and the attachment (typically a bucket), translating hydraulic cylinder force into controlled linear and rotational motion. Its primary role is to provide the necessary reach, leverage, and force application for digging, lifting, and material placement tasks. The component's geometry, pin connections, and structural integrity directly influence the machine's digging depth, breakout force, and overall operational envelope.

The arm operates on lever and linkage principles. It is connected to the boom via a pivot pin at its proximal end and to the bucket via another pivot pin at its distal end. One or more hydraulic cylinders (the arm cylinder) are mounted between the boom and the arm. When hydraulic pressure is applied to extend or retract this cylinder, it exerts a force on the arm, causing it to rotate about its boom connection pin. This rotation moves the attached bucket in an arc, enabling the digging (crowd) and dumping motions. The mechanical advantage is determined by the cylinder mounting points and the arm's geometry.