Pitman Arm

A Pitman arm is a shaft that translates rotary or angular movement into linear movement, or vice versa. Pitman arms are commonly found in water pumping

windmill A windmill is a structure that converts wind power into rotational energy using vanes called windmill sail, sails or blades, specifically to mill (grinding), mill grain (gristmills), but the term is also extended to windpumps, wind turbines, and ...

s, automotive

steering Steering is a system of components, linkages, and other parts that allows a driver to control the direction of the vehicle. Introduction The most conventional steering arrangement allows a driver to turn the front wheels of a vehicle using ...

systems, and

sewing machine A sewing machine is a machine used to sew fabric and materials together with thread. Sewing machines were invented during the first Industrial Revolution to decrease the amount of manual sewing work performed in clothing companies. Since the inv ...

s. In windmills, the Pitman arm connects the driving gear to the pumping arm. It translates the rotary power from the wind blades to the up-and-down motion of the pumping arm. In automotive or truck steering systems, the Pitman arm acts as a

linkage Linkage may refer to: * ''Linkage'' (album), by J-pop singer Mami Kawada, released in 2010 *Linkage (graph theory), the maximum min-degree of any of its subgraphs *Linkage (horse), an American Thoroughbred racehorse * Linkage (hierarchical cluster ...

attached to the

steering box Steering is a system of components, linkages, and other parts that allows a driver to control the direction of the vehicle. Introduction The most conventional steering arrangement allows a driver to turn the front wheels of a vehicle using ...

(see

recirculating ball Recirculating ball, also known as recirculating ball and nut or worm and sector, is a steering mechanism commonly found in older automobiles, off-road vehicles, and some trucks. Most newer cars use the more economical rack and pinion steering ins ...

)

sector shaft Sector may refer to: Places * Sector, West Virginia, U.S. Geometry * Circular sector, the portion of a disc enclosed by two radii and a circular arc * Hyperbolic sector, a region enclosed by two radii and a hyperbolic arc * Spherical sector, a po ...

, it converts the angular

motion In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and mea ...

of the sector shaft into the

linear Linearity is the property of a mathematical relationship (''function'') that can be graphically represented as a straight line. Linearity is closely related to '' proportionality''. Examples in physics include rectilinear motion, the linear r ...

motion needed to steer the

wheel A wheel is a circular component that is intended to rotate on an axle Bearing (mechanical), bearing. The wheel is one of the key components of the wheel and axle which is one of the Simple machine, six simple machines. Wheels, in conjunction wi ...

s. The arm is supported by the sector shaft and supports the

drag link A drag link converts rotary motion from a crank arm, to a second bellcrank, usually in an automotive steering system. While the origin of the term is not clear, it pre-dates the automobile, and is described as in use in 1849 as a means of rotating ...

or center link with a

ball joint In an automobile, ball joints are spherical bearings that connect the control arms to the steering knuckles, and are used on virtually every automobile made. They bionically resemble the ball-and-socket joints found in most tetrapod animals. ...

. It transmits the motion it receives from the steering box into the drag (or center) link, causing it to move left or right to turn the wheels in the appropriate direction. The

idler arm On an automobile or truck with a conventional parallelogram steering linkage, the idler arm or idler arm assembly is a pivoting support for the steering linkage. The idler arm supports the end of the center link on the passenger's side of the ve ...

is attached between the opposite side of the center link from the Pitman arm and the vehicle's frame to hold the center or drag link at the proper height. "Pitman arm" can also refer to a component in a treadle sewing machine that connects the foot pedal to the crankshaft of the lower

flywheel A flywheel is a mechanical device which uses the conservation of angular momentum to store rotational energy; a form of kinetic energy proportional to the product of its moment of inertia and the square of its rotational speed. In particular, ass ...

. In this case, the Pitman arm works similarly to a connecting rod in an engine in which the up and down force applied at one end of the arm translates to pushing and pulling alternately on the eccentric part of the crankshaft to achieve continuous rotation of the crankshaft and flywheel. The bearing connecting the Pitman arm to the crankshaft is known as the Pitman bearing. Early Pitman arms (up until around 1905) were made of wood, whereas later Pitman arms were made of steel. Wooden Pitman arms usually employed a simple wooden bushing around a steel shaft at both ends. The later steel Pitman arms usually used a ball joint at the lower pivot point and a ball bearing for the Pitman bearing at the top. Automotive steering technologies {{Automotive-part-stub