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Squash-Ball-Catapult-Engineering

Design and mathematical analysis of an adjustable MDF catapult for variable range targeting.

Squash Ball Catapult Engineering Project - Group 11

This repository documents the design, mathematical analysis, and manufacture of an adjustable catapult built by Group 11 at Birmingham City University.

🎯 Project Overview

The objective was to design and build a catapult to launch squash balls at targets between 1–5 metres.

📐 Constraints

  • Materials: A single 600 x 600 x 9 mm piece of MDF.
  • Fasteners: Maximum of 30 individual semi-permanent fasteners (nuts, bolts, and washers).
  • Adjustability: The design must be "settable" for variable distances.

Final Physical Build

The final physical prototype, hand-cut from 9mm MDF.

🛠 Engineering Methodology

1. Research & Concept Selection

We researched three traditional catapult styles: the Ballista, Trebuchet, and Mangonel.

  • Morphological Analysis: We compared different sub-functions, such as power sources (elastic stretching vs. twisting) and projectile holders (slings vs. cups).

Morphological Analysis

Morphological analysis used to address feasability concerns.

  • Pugh Matrix: We evaluated three concepts against criteria like ease of manufacture and simplicity. Concept 3 was selected with a grand total of 78 points.

Pugh Matrix

Decision-making matrix used to objectively select the final design.

2. Mathematical Analysis

We conducted a series of experiments to find the spring constant ($k$) of the rubber bands using Hooke's Law: $$F = -kx$$

Hooke's Law table

Ballistic Range Calibration: Using ballistic motion equations and adjusting for drag, we developed a precise setting guide for the catapult:

Range Table

Settings required to hit targets between 1m and 5m.

💻 Technical Design

CAD Modeling (CATIA)

The catapult was modeled using CATIA, creating an assembly of five distinct parts: the base, two sides, a post, and the swing arm.

CAD Assembly

Full assembly render showcasing the adjustable release points.

Technical Drawings

  • Base Dimensions: 350mm length.
  • Swing Arm: 300mm length with a 40mm pivot width.
Side View Front View
Side Drawing Front Drawing

📈 Manufacturing & Reflection

Pivot to Hand-Cutting

Due to the laser cutter being unavailable, we generated a DXF template and cut the pieces out by hand. While this introduced potential human error in accuracy, it proved our design remained within material constraints.

Problem Solving & Results

  • Lateral Motion: We identified that the arm would throw off-center due to lateral movement. We overcame this by replacing nuts with MDF spacers to stabilize the arm.
  • Consistency: By repeating tests 3 times per distance to find a mean average, we achieved consistent target hits.

Full project available at Catapult-project.pptx