A bell crank is a type of crank that changes motion around a 90 degree angle. The name comes from its first use, changing the vertical pull on a rope to a horizontal pull on the striker of a bell, used for calling servants in upper class British households. A crank is a bent portion of an axle, or shaft, or an arm keyed at right angles to the end of a shaft, by which motion is imparted to or received from it; also used to change circular into reciprocating motion, or reciprocating into circular motion. ... A bell is a simple sound-making device. ...
The bell crank consists of an "L" shaped crank pivoted where the two arms of the L meet. Moving rods (or ropes) are attached to the ends of the L arms. When one is pulled, the L rotates around the pivot point, pulling on the other arm.
Changing the length of the arms changes the mechanical advantage of the system. Many applications do not change the direction of motion, but instead to amplify a force "in line", which a bell crank can do in a limited space. In physics and engineering, mechanical advantage (MA) is the factor by which a machine multiplies the force put into it. ...
The crank, instead of being made up as described above, may be formed by bending the shaft to the required shape, as sometimes in the handle of a winch.
Crank is also the name given to a labour machine used in prisons as a means of punishment (see Tread-Mill).
"Crank" or "crank-sided" is a nautical term used of a ship which by reason of her build or from want of balance is liable to overturn.
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