Bell crank

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.

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. There is a tradeoff between range of motion, linearity of motion, and size. The greater the angle traversed by the crank, the more non-linear the motion becomes (the more the motion ratio changes).

External links

* [http://www.flying-pig.co.uk/mechanisms/pages/bellcrank.html Bell Crank]


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Look at other dictionaries:

  • Bell crank — A lever whose two arms form a right angle, or nearly a right angle, having its fulcrum at the apex of the angle. It is used in bell pulls and in changing the direction of bell wires at angles of rooms, etc., and also in machinery. [1913 Webster] …   The Collaborative International Dictionary of English

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  • bell crank — bell cranked, adj. Mach. a lever or rocker having two arms meeting at a pivot at a right angle, used for transmitting motion between two parts meeting at an angle. [1880 85] * * * …   Universalium

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