Milk-Jug Propelled Projectile Launcher

This project required the design and fabrication of a mechanically sound launching system capable of propelling a repurposed-plastic projectile 10 metres using only the pressure generated by collapsing a standard 4-litre milk jug with one foot. The exercise demanded rigorous adherence to constraints, thoughtful material selection, and an ability to translate conceptual sketches into a functional physical prototype. The final mark—97%—reflected excellence across ideation, construction quality, system performance, and aesthetic refinement.

Problem

To engineer a stable, ground-level launching system and a fully repurposed-plastic projectile that could consistently reach the 10-metre target distance with high accuracy, while meeting strict constraints on materials, fabrication methods, and user-applied force. Constraints included: the only permissible source of energy being manual compression of a 4L milk/water jug by stepping on it; launching pad free-standing with no ground anchoring; projectile constructed strictly from repurposed plastic materials; minimal use of adhesives and tape; projectile must remain intact as a single unit throughout flight.

Approach

The design process focused on isolating the system into three primary subsystems: Energy Transfer System (converting jug collapse into coherent airflow), Nozzle Dynamics (controlling the pressure gradient and directing thrust), and Projectile Aerodynamics (designing a stable flight body from repurposed components with minimal drag).

I produced three divergent sketches examining vertical, inclined, and modular loading configurations. The final build adopted a space-station aesthetic with a rigid truss-style frame, angled intake chamber, low-friction launch rail, and optimised nozzle tube. The projectile (Version 3) was lightweight, drag-reduced, and flight-stable, formed from pool noodle segments and repurposed packaging plastics.

Methods & Tools

• Applied fluid dynamics to low-pressure pneumatic systems
• Structural design and mechanical layout under constrained materials
• Rapid prototyping methodology (sketch → model → prototype → refinement)
• Iterative testing and quantitative performance improvement
• 3D concept exploration and system architecture design
• Material selection and repurposing techniques

Outcome

• Achieved 10.2 m on second attempt, surpassing the 10-metre threshold
• Received full marks (12/12) for initial concept exploration
• Received full marks (13/13) for physical prototype
• Awarded 19/20 for achieved distance
• Awarded 38/40 for launching system impression
• Awarded 15/15 for projectile impression
• Overall Grade: 97/100 (A+)

Key Leverage

This project showcased the importance of precision in both design intent and fabrication discipline. By treating a simple constraint—a collapsing milk jug—as a controllable energy source, I demonstrated the ability to extract performance from limited inputs through careful engineering judgement. The final system's consistency and accuracy reflected a rigorous conceptual foundation and a commitment to meticulous execution.