Editing Trebuchet (section)

== Basic design ==
[[File:Trebuchet2.png|thumb|Side view of counterweight trebuchet, with a detail of the counterweight release mechanism]]

The trebuchet is a [[compound machine]] that makes use of the [[mechanical advantage]] of a [[lever]] to throw a projectile. They are typically large constructions, with the length of the beam as much as {{convert|15|m|-1|sp=us}}, with some purported to be even larger.{{sfn|Saimre|2007|p=66}}

A trebuchet consists primarily of a long beam attached by an [[axle]] suspended high above the ground by a stout frame and base, such that the beam can rotate vertically through a wide arc (typically over 180°). A [[sling (weapon)|sling]] is attached to one end of the beam to hold the projectile. The projectile is thrown when the beam is quickly rotated by applying [[force]] to the opposite end of the beam. The [[mechanical advantage]] is primarily obtained by having the projectile section of the beam much longer than the opposite section where the force is applied – usually four to six times longer.{{sfn|Saimre|2007|p=65}}

[[File:Mangonneau4.png|thumb|left|Example sling-release mechanism that automatically launches projectile at desired point of arm swing]]

The difference between counterweight and traction trebuchets is what force they use. Counterweight trebuchets use gravity; [[potential energy]] is stored by slowly raising an extremely heavy box (typically filled with stones, sand, or lead) attached to the shorter end of the beam (typically on a hinged connection), and releasing it on command.

Traction trebuchets use [[human power]]; on command, men pull ropes attached to the shorter end of the trebuchet beam. The difficulties of coordinating the pull of many men together repeatedly and predictably makes counterweight trebuchets preferable for the larger machines, though they are more complicated to engineer.{{sfn|Saimre|2007|p=64}} The trebuchet had further modifications to allow an increase to its range, by creating a slot for the sling and projectile to sit underneath the trebuchet, enabling the sling to be lengthened and thus extending the range, an alteration in the trajectory, or the release point to be changed.{{sfn|Chevedden|1995|p=3}} Further increasing their complexity is that either [[winch]]es or [[treadwheel]]s, aided by [[block and tackle]], are typically required to raise the more massive counterweights. So while counterweight trebuchets require significantly fewer men to operate than traction trebuchets, they require significantly more time to reload. In a long siege, reload time may not be a critical concern.

When the trebuchet is operated, the force causes [[rotational acceleration]] of the beam around the axle (the [[:wikt:fulcrum|fulcrum]] of the lever). These factors multiply the acceleration transmitted to the throwing portion of the beam and its attached sling. The sling starts rotating with the beam, but rotates farther (typically about 360°) and therefore faster, transmitting this increased speed to the projectile. The length of the sling increases the mechanical advantage, and also changes the [[trajectory]] so that, at the time of release from the sling, the projectile is traveling in the desired [[Ballistics|speed and angle]] to give it the range to hit the target. Adjusting the sling's release point is the primary means of fine-tuning the range, as the rest of the trebuchet's actions are difficult to adjust after construction.

The rotation speed of the throwing beam increases smoothly, starting slow but building up quickly. After the projectile is released, the arm continues to rotate, allowed to smoothly slow down on its own accord and come to rest at the end of the rotation. This is unlike the violent sudden stop inherent in the action of other catapult designs such as the [[Onager (weapon)|onager]], which must absorb most of the launching energy into their own frame, and must be heavily built and reinforced as a result. This key difference makes the trebuchet much more durable, allowing for larger and more powerful machines.<ref>{{cite book |last1=Denny |first1=Mark |title=Ingenium : five machines that changed the world |date=2007 |publisher=Johns Hopkins University Press |isbn=978-0801898464 |pages=66–70}}</ref>

A trebuchet projectile can be almost anything, even debris, [[Animal carcass|rotting carcasses]], or [[Early thermal weapons|incendiaries]], but is typically a large stone. Dense stone, or even metal, specially worked to be round and smooth, gives the best range and predictability. When attempting to breach enemy walls, it is important to use materials that will not shatter on impact; projectiles were sometimes brought from distant quarries to get the desired properties.{{sfn|Saimre|2007|p=73}}