 | This article needs additional citations for verification .(January 2021) |
A bellcrank is a type of crank that changes motion through an angle. The angle can range from 0 to 360 degrees, but 90-degree and 180-degree bellcranks are most common.
The name comes from its first use, changing the vertical pull on a rope to a horizontal pull on the striker of a bell to sound it.
A typical 90-degree bellcrank consists of an L-shaped crank pivoted where the two arms of the L meet. Moving rods or cables are attached to the outer ends of the L. When one is pulled, the L rotates around the pivot point, pulling on the other rod.
A typical 180-degree bellcrank consists of a straight bar that pivots at or near its center. When one rod is pulled or pushed, the bar rotates around the pivot point, pulling or pushing on the other rod.
Changing the length of the bellcrank's arms changes the mechanical advantage of the system. Many applications do not change the direction of motion but instead amplify a force "in line", which a bellcrank 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 the motion ratio changes, and the more non-linear the motion becomes.[ citation needed ]
Bellcranks are often used in aircraft flight control systems to connect the pilot's controls to the control surfaces. For example, on light aircraft, the rudder often has a bellcrank (also called a control horn) whose pivot point is the rudder hinge. A cable connects one of the pilot's rudder pedal to one side of the bellcrank. When the pilot pushes the rudder pedal, the cable pulls the bellcrank, causing the rudder to rotate. The opposite rudder pedal is connected to the other end of the bellcrank to rotate the rudder in the opposite direction.
Bellcrank mechanisms were installed at the top of entryway stairs in multi-unit Victorian and Edwardian homes (c. 1890 to 1930), particularly in the San Francisco Bay Area, to allow residents to open and close the doors remotely so they would not need to walk down the stairs to welcome guests. [1]
Bellcranks are also seen in automotive applications, such as in the linkage connecting the throttle pedal to the carburetor or connecting the brake pedal to the master cylinder.
In vehicle suspensions, bellcranks are used in pullrod and pushrod suspensions in cars or in the Christie suspension in tanks. More vertical suspension designs such as MacPherson struts may not be feasible in some vehicle designs due to space, aerodynamic, or other design constraints; bellcranks translate the vertical motion of the wheel into horizontal motion, allowing the suspension to be mounted transversely or longitudinally within the vehicle.
Bellcranks are used in some internally geared hub assemblies to select gears. [2] [3] The motion from a Bowden cable is translated by a bellcrank to a push rod, which selects which portion of the epicyclic gears are driven by the bicycle's rear sprocket.
A bicycle brake reduces the speed of a bicycle or prevents the wheels from moving. The two main types are: rim brakes and disc brakes. Drum brakes are less common on bicycles.
A derailleur is a variable-ratio bicycle gearing system consisting of a chain, multiple sprockets of different sizes, and a mechanism to move the chain from one sprocket to another.
The crankset or chainset is the component of a bicycle drivetrain that converts the reciprocating motion of the rider's legs into rotational motion used to drive the chain or belt, which in turn drives the rear wheel. It consists of one or more sprockets, also called chainrings or chainwheels attached to the cranks, arms, or crankarms to which the pedals attach. It is connected to the rider by the pedals, to the bicycle frame by the bottom bracket, and to the rear sprocket, cassette or freewheel via the chain.
Steering is the control of the direction of motion or the components that enable its control. Steering is achieved through various arrangements, among them ailerons for airplanes, rudders for boats, cylic tilting of rotors for helicopters, and many more.
The pedal is the part of a bicycle that the rider pushes with their foot to propel the vehicle. It provides the connection between the cyclist's foot or shoe and the crank allowing the leg to turn the bottom bracket spindle and propel the bicycle's wheels. A pedal usually consists of a spindle that threads into the end of the crank, and a body on which the foot rest is attached, that is free to rotate on bearings with respect to the spindle.
Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude.
A crank is an arm attached at a right angle to a rotating shaft by which circular motion is imparted to or received from the shaft. When combined with a connecting rod, it can be used to convert circular motion into reciprocating motion, or vice versa. The arm may be a bent portion of the shaft, or a separate arm or disk attached to it. Attached to the end of the crank by a pivot is a rod, usually called a connecting rod (conrod).
In mechanical engineering, an eccentric is a circular disk solidly fixed to a rotating axle with its centre offset from that of the axle.
A fixed-gear bicycle is a bicycle that has a drivetrain with no freewheel mechanism such that the pedals always will spin together with the rear wheel. The freewheel was developed early in the history of bicycle design but the fixed-gear bicycle remained the standard track racing design. More recently the "fixie" has become a popular alternative among mainly urban cyclists, offering the advantage of simplicity compared with the standard multi-geared bicycle.
A double wishbone suspension is an independent suspension design for automobiles using two wishbone-shaped arms to locate the wheel. Each wishbone or arm has two mounting points to the chassis and one joint at the knuckle. The shock absorber and coil spring mount to the wishbones to control vertical movement. Double wishbone designs allow the engineer to carefully control the motion of the wheel throughout suspension travel, controlling such parameters as camber angle, caster angle, toe pattern, roll center height, scrub radius, scuff, and more.
In the study of mechanisms, a four-bar linkage, also called a four-bar, is the simplest closed-chain movable linkage. It consists of four bodies, called bars or links, connected in a loop by four joints. Generally, the joints are configured so the links move in parallel planes, and the assembly is called a planar four-bar linkage. Spherical and spatial four-bar linkages also exist and are used in practice.
After about 1910, the Baker valve gear was the main competitor to Walschaerts valve gear for steam locomotives in the United States. Strictly speaking it was not a valve gear but a variable expansion mechanism adapted to the Walschaerts layout replacing the expansion link and sliding die block. The Baker arrangement used more pivot bearings or pin joints, but avoided the die slip inherent to the expansion link, with the aim of lessening wear and the need for service; it could also facilitate longer valve travel.
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.
Southern valve gear was briefly popular on steam locomotives in the United States. It combines elements of the Walschaerts and Baker patterns.
In a reciprocating engine, the dead centre is the position of a piston in which it is either farthest from, or nearest to, the crankshaft. The former is known as top dead centre (TDC) while the latter is known as bottom dead centre (BDC).
Bicycle suspension is the system, or systems, used to suspend the rider and bicycle in order to insulate them from the roughness of the terrain. Bicycle suspension is used primarily on mountain bikes, but is also common on hybrid bicycles.
The Leavitt-Riedler Pumping Engine (1894) is a historic steam engine located in the former Chestnut Hill High Service Pumping Station, in Boston, Massachusetts. It has been declared a historic mechanical engineering landmark by the American Society of Mechanical Engineers. The pumping station was decommissioned in the 1970s, and turned into the Metropolitan Waterworks Museum in 2011.
A slider-crank linkage is a four-link mechanism with three revolute joints and one prismatic (sliding) joint. The rotation of the crank drives the linear movement of the slider, or the expansion of gases against a sliding piston in a cylinder can drive the rotation of the crank.