Whippletree (mechanism)
Encyclopedia
A whippletree or whiffletree is a mechanism to distribute force evenly through linkages. The mechanism may also be referred to as an equalizer, leader bar or double tree. It consists of a bar pivoted at or near the centre, with force applied from one direction to the pivot
, and from the other direction to the tips. Several whippletrees may be used in series to distribute the force further, such as to simulate pressure over an area as when applying loading to test plane wings. Whippletrees may be used either in compression or tension. Whippletrees were also used for subtraction and addition calculations in mechanical computers.
s are the chains or straps on each side of the harness, on which the animal pulls). For these, the whippletree consists of a loose horizontal bar between the draught animal and its load. The centre of the bar is connected to the load, and the traces attach to its ends. Whippletrees are used especially when pulling a dragged load such as a plough
, harrow
, log or canal boat
or for pulling a vehicle (by the leaders in a team with more than one row of animals).
A swingletree
or singletree is a special kind of whippletree used for a horse-drawn vehicle
, and the term swingletree is sometimes used for draught whippletrees generally.
A whippletree balances the pull from each side of the animal, preventing the load from tugging alternately on each side. It also keeps a point load from pulling the traces in onto the sides of the animal.
If several animals are used abreast, further whippletrees may be used behind the first. Thus, with two animals, each will have its own whippletree, then a further whippletree will balance the loads from their two whippletrees – this arrangement is sometimes known as a double-tree, or for the leaders in a larger team, leader-bars. With three or more animals abreast, even more whippletrees are needed; some may be made asymmetrical to balance odd numbers of animals. Multiple whippletrees balance the pulls from the different animals, ensuring that each takes an equal share of the work.
s, mower
s or roller
s to a tractor
. In this case the effect is to combine several small loads to a single load at the tractor hitch (the reverse of the use for draught animals).
A series of whippletrees is used in compression in a standard windshield wiper, to distribute the point force of the sprung wiper arm evenly along the wiper blade.
s are three-dimensional designs since the tree has to use support multiple points over an area.
One widely-used practical application of such linkages was in the IBM Selectric typewriter, where they summed binary mechanical inputs to rotate and tilt the type ball. This type of computer was also used for naval gunnery
, such as the MK 56 Gun Fire Control System and sonar
fire-control system
s.
Lever
In physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to either multiply the mechanical force that can be applied to another object or resistance force , or multiply the distance and speed at which the opposite end of the rigid object travels.This leverage...
, and from the other direction to the tips. Several whippletrees may be used in series to distribute the force further, such as to simulate pressure over an area as when applying loading to test plane wings. Whippletrees may be used either in compression or tension. Whippletrees were also used for subtraction and addition calculations in mechanical computers.
Draught whippletrees
Whippletrees are used in tension to distribute forces from a point load to the traces of draught animals (the traceTrace (tack)
In transport, a trace is one of two, or more, straps, ropes or chains by which a carriage or wagon, or the like, is drawn by a harness horse or other draught animal. The once popular idiom: "kick over the traces" comes from a frisky animal kicking one or both feet outside a trace...
s are the chains or straps on each side of the harness, on which the animal pulls). For these, the whippletree consists of a loose horizontal bar between the draught animal and its load. The centre of the bar is connected to the load, and the traces attach to its ends. Whippletrees are used especially when pulling a dragged load such as a plough
Plough
The plough or plow is a tool used in farming for initial cultivation of soil in preparation for sowing seed or planting. It has been a basic instrument for most of recorded history, and represents one of the major advances in agriculture...
, harrow
Harrow (tool)
In agriculture, a harrow is an implement for breaking up and smoothing out the surface of the soil. In this way it is distinct in its effect from the plough, which is used for deeper tillage. Harrowing is often carried out on fields to follow the rough finish left by ploughing operations...
, log or canal boat
Canal boat
There are three articles associated with canal watercraft:* The Volunteer - A replica 1848 canal boat docked on the Illinois and Michigan Canal at LaSalle, Illinois* Narrowboat - a specialized craft for operation in early narrow canals...
or for pulling a vehicle (by the leaders in a team with more than one row of animals).
A swingletree
Swingletree
A swingletree or singletree is a wooden or metal bar used to balance the pull of a draught horse or other draught animal when pulling a vehicle. It is a kind of whippletree, and the term is also used sometimes for other whippletrees.It is a horizontal bar, attached or suspended in the middle,...
or singletree is a special kind of whippletree used for a horse-drawn vehicle
Horse-drawn vehicle
A horse-drawn vehicle is a mechanized piece of equipment pulled by one horse or by a team of horses. These vehicles typically had two or four wheels and were used to carry passengers and/or a load...
, and the term swingletree is sometimes used for draught whippletrees generally.
A whippletree balances the pull from each side of the animal, preventing the load from tugging alternately on each side. It also keeps a point load from pulling the traces in onto the sides of the animal.
If several animals are used abreast, further whippletrees may be used behind the first. Thus, with two animals, each will have its own whippletree, then a further whippletree will balance the loads from their two whippletrees – this arrangement is sometimes known as a double-tree, or for the leaders in a larger team, leader-bars. With three or more animals abreast, even more whippletrees are needed; some may be made asymmetrical to balance odd numbers of animals. Multiple whippletrees balance the pulls from the different animals, ensuring that each takes an equal share of the work.
Other agricultural whippletrees
Whippletrees may also be used in modern agriculture, for example to link several ganged agricultural implements such as harrowHarrow (tool)
In agriculture, a harrow is an implement for breaking up and smoothing out the surface of the soil. In this way it is distinct in its effect from the plough, which is used for deeper tillage. Harrowing is often carried out on fields to follow the rough finish left by ploughing operations...
s, mower
Mower
A mower is a machine for cutting grass or other plants that grow on the ground. Usually mowing is distinguished from reaping, which uses similar implements, but is the traditional term for harvesting grain crops, e.g...
s or roller
Roller (agricultural tool)
The roller is an agricultural tool used for flattening land or breaking up large clumps of soil, especially after ploughing. Typically, rollers are pulled by tractors or, prior to mechanisation, a team of animals such as horses or oxen....
s to a tractor
Tractor
A tractor is a vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction...
. In this case the effect is to combine several small loads to a single load at the tractor hitch (the reverse of the use for draught animals).
Windshield (windscreen) wipers
Telescopes
Some designs for large telescopes use whippletrees, to support the optical elements. The tree provides for distributed mechanical support, thereby reduces localised mechanical deflections, which in turn reduces optical distortion. Unlike the applications described above, which are two dimensional, the whippletrees in telescope mirror support cellMirror support cell
In astronomy the mirror support cell - more commonly mirror cell - is the component of a reflecting telescope which supports the mirror in place to hold optical alignment, allow collimation adjustment, and protect it from falling out...
s are three-dimensional designs since the tree has to use support multiple points over an area.
Mechanical analogue computers
Linkage-type mechanical analog computers use whippletree linkages to add and subtract quantities represented by straight-line motions. The illustration here of whippletrees for a three-animal team is very similar to a group of linkage adders and subtracters: "load" is the equivalent of the output sum/difference of the individual inputs. Inside the computer, cylinders on the knob shafts have thin metal tapes wrapped around them to convert rotary to linear motion.One widely-used practical application of such linkages was in the IBM Selectric typewriter, where they summed binary mechanical inputs to rotate and tilt the type ball. This type of computer was also used for naval gunnery
Naval artillery
Naval artillery, or naval riflery, is artillery mounted on a warship for use in naval warfare. Naval artillery has historically been used to engage either other ships, or targets on land; in the latter role it is currently termed naval gunfire fire support...
, such as the MK 56 Gun Fire Control System and sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...
fire-control system
Fire-control system
A fire-control system is a number of components working together, usually a gun data computer, a director, and radar, which is designed to assist a weapon system in hitting its target. It performs the same task as a human gunner firing a weapon, but attempts to do so faster and more...
s.
See also
- Boat trailerBoat trailerA boat trailer is a trailer designed to launch, retrieve, carry and sometimes store boats.-Commercial boat trailers:Commercial hydraulic boat trailers are used by marinas, boatyards, boat hauliers, boat dealers and boat builders...
, which uses this mechanism to evenly distribute force across the hull of the boats it carries. - Differential (mechanical device), which does for torque what each layer of a whippletree does for force.
- Draught animal
- Draught horse
- Horse collarHorse collarA horse collar is a part of a horse harness device used to distribute load around a horse's neck and shoulders when pulling a wagon or plow. The collar often supports and pads a pair of curved metal or wood pieces, called hames, to which the traces of the harness are attached...
- Horse harnessHorse harnessA horse harness is a type of horse tack that allows a horse or other equine to pull various horse-drawn vehicles such as a carriage, wagon or sleigh. Harnesses may also be used to hitch animals to other loads such as a plow or canal boat....
- Mobile (sculpture)Mobile (sculpture)A mobile is a type of kinetic sculpture constructed to take advantage of the principle of equilibrium. It consists of a number of rods, from which weighted objects or further rods hang. The objects hanging from the rods balance each other, so that the rods remain more or less horizontal...
, similar principles applied in art. - Paraglider wing, in which a load is distributed by multiple strings, but without rigid elements.
- PLate OPtimizerPLate OPtimizerPLate OPtimizer, or PLOP is a CAD program used by amateur telescope makers to design primary mirror support cells for reflecting telescopes. It was developed by telescope maker David Lewis, first described in 1999, and used to simplify calculations needed in the design of mirror support cells...
, CAD program for distribution of whippletree support elements in telescope mirror cell design - Proteus (WAM-V)Proteus (WAM-V)The MAR Proteus is an experimental watercraft developed by Marine Advanced Research. The MAR Proteus is the first vessel of the Wave Adaptive Modular Vessel-type. The vessel was developed by Ugo Conti. Because of its use of four legs connecting the superstructure to the outriggers, the ship has...
, catamaran with whippletree suspension - SwingletreeSwingletreeA swingletree or singletree is a wooden or metal bar used to balance the pull of a draught horse or other draught animal when pulling a vehicle. It is a kind of whippletree, and the term is also used sometimes for other whippletrees.It is a horizontal bar, attached or suspended in the middle,...
External links
- Photo of whippletree for draught horses by Beig Alert on Flickr (Note: this photo shows three muddled sets of whippletrees: one single, one double and one triple.)
- Photo InTheHead of a windshield wiper's whippletree by Barefoot on Flickr
- Major telescopes from Lord Rosse to about 1980
- [ftp://ftp.aao.gov.au/pub/local/will/pilot/PG_notes/pilot%20m1%20support.doc/ Support of PILOT primary mirror by Peter Gillingham 2 March 2007 ]
- Mirror Edge Support Calculator
- Archived set of images of mechanical computer.