engineering the trebuchet design process presentation
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Trebuchet: An Exploration of Ballistics
Presentation by:Panayotis Manganaris
Project in collaboration with:Jack Mangan
Chandler Owens
Understanding: what is a trebuchet?
● Create a special sort of catapult that functions on the leverage of a counterweight acting on a projectile rather than the deformation of springs or lengths of material
L-3: sling
L-2 + L-5: arm
H: ground to axle
M1: Weight
M3: Projectile
Understanding: Criteria to meet
● Design and build a trebuchet to lob a squash ball to a recommended distance of at least 30 feet
– Be competitive to enter Trebuchet Competition
● Counterweight consists of three 305-326 grams Campbell's Tomato Soup cans.
– Create apparatus to secure weight to arm.
● Lever arm + sling hook must not exceed 0.8 meters in length
– Must be delicately balanced to pass the “pencil test”
● Axle around which the arm rotates must not be above 0.4 meters from the ground
Explore: Possibilities and designs
● Possible trebuchet types
– Floating arm
– Recoiling – Dismissed due to the observation that it probably just wastes valuable energy at this scale
– Swinging arm
● Design Objectives
– Maximize the transfer of energy from the falling weight to the projectile
● Minimize friction between the arm and the axle● Balance the lever precisely through tapering
– Maximize accuracy and distance to serve as the ranged artillery in the Trebuchet Competition
Explore: What design standards work best?
● The ideal ratio of short to long arm is 1 to 4
– Likely 1-3 to1-2 in this scale
● The sling should be as long as the long arm
● Using a lubricated ball-bearing to minimize friction in the pivot
● Inertia of components is as low as possible
Swinging Arm
Floating Arm
Define: Choosing the swinging arm
● Build floating arm?
– Floating arm more efficient, more powerful
– Not compact enough to easily pass inspection (ambiguous as to where the actual “axle” is, so maybe too tall), no guarantee of high accuracy, difficult to reload and fire
● Or, build standard swinging arm?
– Less efficient, powerful (deficits likely not noticeable at this scale)
– Absolute certainty as to the location of the axle, easy to meet requirements, can be modified in prototyping to increase accuracy more easily
– Option to Introduce a guiding rail along the bottom of the platform
● Possibly increasing the accuracy of each throw
Define: Approximating the best swinging arm
● Short arm: 20cm● Long arm: 60cm● Sling length: 60cm● Weight: 0.978 kilograms● Projectile: 0.043 Kilogram● Center of gravity:
Within 10 cm of pivot on
long arm's side
Ideate: Simulations
● Very difficult to calculate precise measurements necessary to make the best swinging arm trebuchet
● virtualtrebuchet.com helped to pinpoint best measurements from approximations
● Updated Measurements after multiple virtual trials:– Short arm: 24cm
– Long arm: 56cm
– Sling length: 56cm
– Weight: 1.05 kilograms (selected and measured cans)
– Projectile: 0.043 Kilogram
– Center of gravity: 3 cm from pivot on long arm's side
Ideate: Solving structural challenges
● The two foreseeable challenges will be the mechanics of the sling and the method of attaching the weight cans to the short arm
● secure cans using nails to form stable shelf and strap in with duct tape
● Use boline knots in fishing wire to secure sling to arm and loop around release hook
Basic Pouch Idea
ReleaseHook
Sling and pouchassembly
Throwing Arm
Ideate: Blueprint● Defining Material
Requirements● 16ft of 2x4
● 3ft of 1x4
● 1m of 1/2x2 hardwood
● Light, thin cloth
● 5 large washers for ¼in. threaded metal rod
● 3 small washers
● 8 ¼in. Nuts
● 3inch screws
● Gorilla Glue
● R4AZZ mini ball bearing
Prototype: Simulating blueprint
● 9.947m = 32.6ft simulated maximum● Note: Inertia of arm and of weight must be minimal
– Keep the structure of arm as light as possible
Prototype: Building and testing
● Trebuchet was built precisely to specifications
● Tapering of arm was done by feeling
– No time to use Inventor modeling
● First Launch:http://youtu.be/NYJJEI4Yfxk
Guiding rail
Prototype: Specific construction notes
Due to the slipping of nuts against the arm surface, the method of locking nuts against each-other was used to prevent the issue from affecting accuracy.
Showing R4AZZ shielded ball bearing.
● The optimum release angle is 45 degrees– Controlled by adjusting the bend in the hook
● SlowMo Firing Archttp://youtu.be/36lDmrNJELQ
(Also under videos tab)
● Sling secured with
boline knots as
described
Refine: Release angle
Solution: Securing Weights
● Used the previously described nails and duct tape method
Solution: Distance and accuracy
● Construction successful, surpassed expectations
● Testing to compare real distances to simulated expectations, 32.6ft simulated maximum
● 33.3, 34, 30.6, 32.2 feet experimental distances
● Testing for accuracy involved aiming for a pie pan 22 feet ahead and measuring by how many feet it was missed
● margins were by 14, 16, and 28 inches with one misfire occurring during testing
– Note: the challenge was greatest with adjusting to fire only 22 feet instead of the maximum.
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