Engineering the trebuchet design process presentation
- 1. Trebuchet: An Exploration of Ballistics Presentation by: Panayotis Manganaris Project in collaboration with: Jack Mangan Chandler Owens
- 2. 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
- 3. 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
- 4. 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
- 5. 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
- 6. 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
- 7. 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
- 8. 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
- 9. 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 Release Hook Sling and pouch assembly Throwing Arm
- 10. 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
- 11. 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
- 12. 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
- 13. 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.
- 14. ● The optimum release angle is 45 degrees – Controlled by adjusting the bend in the hook ● SlowMo Firing Arc http://youtu.be/36lDmrNJELQ (Also under videos tab) ● Sling secured with boline knots as described Refine: Release angle
- 15. Solution: Securing Weights ● Used the previously described nails and duct tape method
- 16. 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