Jack Hansen
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Whipper trebuchet

A three-link launch mechanism developed through nonlinear dynamics, structural checks, detailed design and physical testing.

Year
2023
Role
Dynamics, simulation and detailed design
Tools
Python, SciPy, Pymunk, SolidWorks
Assembly drawing and bill of materials for the whipper trebuchet
Complete SolidWorks assembly and 26-item bill of materials

Model

Geometry, inertia and release timing are tightly coupled in a whipper trebuchet. I built a first-principles multibody model in Python, using SciPy and Pymunk to select arm ratios, counterweight mass and release configuration before committing to hardware.

3 linksCoupled nonlinear mechanism
30 lbModelled counterweight
>200 ftPredicted still-air range
Trebuchet dynamics model with links, centres of mass and generalized coordinates
Multibody definition used by the Python model

Complete document

Dynamics and design calculations

Five-page derivation, multibody model and structural calculations.

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Detailed design

Loads from the dynamic model informed shaft bending, arm stress and deflection checks. The final SolidWorks package included the full assembly, exploded views, component drawings and a 26-item bill of materials, with adjustment preserved at the most sensitive interfaces.

Exploded technical drawing of the trebuchet arm assembly
Exploded arm assembly and release components

Complete document

Complete drawing package

Assembly, bill of materials, component drawings and exploded views.

Open PDFDownload

Physical test

The manufactured mechanism was tested with tennis-ball projectiles. Friction, flexibility and release behaviour exposed the limits of the clean numerical model and provided a basis for calibration.

Completed whipper trebuchet outdoors before testing
Completed mechanism prepared for testing
Trebuchet test footage
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