Student designed trebuchet to be used in interscholastic competition. Built to fit within qualifying criteria, the challenge became maximizing range and accuracy in order to selectively engage and destroy enemy targets while staying out of range. Ultimately the contest was lost, but this trebuchet performed to expectations. Consistently lobbing a squash ball projectile over 30 feet and hitting within a square foot when all other parameters were the same.

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