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Basic Trebuchet Design Tips

A trebuchet is a French name for a medieval war machine that was used to fling projectiles, including boulders, dead horses, and diseased bodies into or over castle walls to soften the defenses in preparation for invasion.

Here are Villiard de Honnecourt's (c. 1250) instructions for building a trebuchet: "If you want to make the strong engine which is called a trebuchet, pay close attention here. Here is the base as it rests on the ground. Here in front are the two windlasses and the double rope with which one draws back the beam ("verge") as you can see on the other page. There is a great weight to pull back, for the counter-poise is very heavy, being a hopper full of earth which is two 'large toises' long and nine feet across and twelve feet deep. ("il i a une huge plainne de terre ki .II. grans toizes a de lonc et .VIIII. pies de le, et .XII. Pies de parfont") Remember the arc of the arrow ("le fleke") when discharged and take great care, because it must be placed against the stanchion in front. "
The above translation is from "War in the Middle Ages" by Philippe Contamine

Problem Statement: You will form a team to design and build a trebuchet.

A successful design will launch a projectile (a tennis ball) which will impact a designated target with a high degree of accuracy. Your design should include provisions for adjusting the range of the impact point.

Object
Design guidelines
Material
Counterweight 75 to 100 times heavier than projectile should be adjustable
Arm angle should be about 45 degrees when cocked; upper part of arm should be 3 to 5 times longer than the lower end pvc pipe
Base and framework must be heavy enough to support arm and counterweight and for precision, yet light enough to have a high material efficiency pvc pipe
Sling or rope should be slightly shorter than upper part of the throwing arm (for starters, that is); too short will release the projectile too early, higher trajectory; too long will drag the ground, lower trajectory any material
Sling release pin a more hooked prong will hold the sling loop longer than a straighter one. ie a prong less hooked or in line with beam gives an earlier release, higher trajectory;a prong more hooked or forward-pointing gives a later release, flatter trajectory metal or other material
Projectile a heavier projectile tends to pull the loop off the prong earlier than a lighter projectile does. heavy projectile gives earlier release, higher trajectory; light projectile gives later release, flatter trajectory tennis ball-provided
Trigger you need some way to release the projectile in a repeatable way any material
Trough the projectile needs to slide down some type of guide; friction will be important here any material
*Base wheels-optional wheels added to the base may increase distance; repeatability(? ) any material

Testing: You are expected to accurately predict the distance that a projectile will be hurled based on your Working Model. A target location will be given (between 30 and 50 ft), and you will have to adjust your trebuchet to cause the projectile to accurately impact the target. See the Grading Criteria sheet for details.

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