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crank,mechanical linkage consisting of a bar attached to a pivot at one of its ends in such a way that it is capable of rotating through a complete circle about the pivot. One of the principal uses of a crank is to turn reciprocating, or back and forth, motion into rotary motion or vice versa. A bell crank is one designed to change the direction of a linear motion.
the simplest rotating part of a crank mechanism. It has a cylindrical projection, the pin, whose axis is displaced relative to the axis of rotation of the crank by a distance r, which may be fixed or variable (see Figure 1).
In a mechanical linkage or mechanism, a link that can turn about a center of rotation. The crank's center of rotation is in the pivot, usually the axis of a crankshaft, that connects the crank to an adjacent link. A crank is arranged for complete rotation (360°) about its center; however, it may only oscillate or have intermittent motion. A bell crank is frequently used to change direction of motion in a linkage (see illustration). See Linkage (mechanism)