Limited Material Trebuchet Design & Manufacture

Overview

Role - Mechanical Designer | Design Engineer | Prototype Fabricator | Testing & Validation

Tools - AutoCAD, Mathematical Modeling, Hand & Power Woodworking Tools

Skills - Mechanical Design, Engineering Analysis, Design Optimization, Rapid Prototyping, Experimental Testing, Manufacturing, Design for Manufacturing (DfM), Structural Design, Team Collaboration 

Design Process

The objective of this project was to design, manufacture, and optimize a trebuchet capable of launching a standard 24 g squash ball the greatest possible distance while complying with strict material, dimensional, and weight constraints. Working in a team of three, every aspect of the design was developed within a limited material budget consisting of five wooden strips, one dowel, specified lengths of cotton and nylon string, wood glue, and a small fabric sling. The completed trebuchet also had to remain below a 1.3 kg weight limit while utilizing one, two, or three standard beverage cans as the counterweight.

To guide the design process, a mathematical model was developed to estimate projectile range based on theoretical energy transfer efficiencies. While published literature demonstrates the performance potential of advanced trebuchet mechanisms, the model highlighted the practical challenges of achieving those efficiencies under the project's material limitations and manufacturing tolerances. This analysis allowed different design concepts to be evaluated before committing to a final architecture.

Three primary configurations were investigated, including a Murlin trebuchet and a traditional swing-arm design. Although the Murlin mechanism offered higher theoretical efficiency, it introduced significantly greater mechanical complexity and a higher risk of inconsistent launches. After evaluating the trade-offs between performance, manufacturability, and reliability, the team selected a traditional swing-arm configuration capable of delivering consistent performance while remaining robust under competition conditions.

To accelerate development, a full-scale prototype was constructed using self-manufactured lumber cut from pine plywood to match the dimensions of the competition materials. Purchasing a table saw enabled rapid fabrication of equivalent stock, allowing the design to be tested and refined before the official materials were used. This iterative approach significantly reduced uncertainty during final manufacturing and provided valuable insight into launch dynamics and structural behavior.

A rigid frame was developed early in the project using double-shear dowel joints to maximize stiffness while minimizing material usage. The modular frame architecture also allowed multiple throwing arm configurations to be evaluated without redesigning the primary structure. Manufacturing of the final trebuchet was completed using hand and power tools before undergoing repeated testing to optimize sling geometry, release timing, and overall launch performance.

An additional optimization focused on maximizing the effective counterweight. Since the counterweight support structure was excluded from the overall weight limit, surplus wood and excess wood glue were strategically incorporated into the carrier assembly, increasing its mass without violating competition rules. This creative interpretation of the design constraints improved the available potential energy while maintaining compliance with all project requirements.

Results

The completed trebuchet achieved a maximum launch distance of 76.5 feet, placing 4th out of more than 60 competing teams. The final design demonstrated excellent structural rigidity, repeatable launch performance, and reliable operation throughout testing and competition.

Beyond the final competition results, the project showcased the importance of balancing theoretical performance with practical engineering considerations. Rather than pursuing the highest-efficiency concept, the design process prioritized reliability, manufacturability, and repeatability through analytical modeling, rapid prototyping, and iterative testing.

This project demonstrates the application of engineering analysis, mechanical design, rapid prototyping, manufacturing, and experimental validation to solve a constrained design challenge. By combining theoretical modeling with hands-on testing and creative optimization within strict competition rules, the team developed a high-performing mechanical system capable of competing successfully against more than 60 teams.