In the Fall of 2013 four students in the ENGR2210 Principles of Engineering course at Olin College built a cannon to shoot marshmallows. Forrest Bourke, Saarth Mehrota, Michael Searing and Elliott Wyse chose the project to meet the course objectives of teamwork, communication and design development.
Four servo motors control the marshmallow loading, the launching, and two axes of movement. An Arduino Uno board controls the mechanism. The system was designed in SolidWorks and built primarily using the college's fabrication resources.
http://confectionerycannon.com/index.html
The students programmed the system using Python and Arduino C, and the programming is available now as open source code on GitHub. The sprinkler valve that acts as the launch release is controlled by a 2N7000 MOSFET transistors and runs on 24V AC.
Material selection is discussed on the website - the students says they chose acrylic for most of the structural pieces over acetal because of the cost benefit. The design tradeoff was that the acrylic wasn't too strong and was often brittle. Acrylic does have the benefit of being easy to lasercut and gives the finished product a great visual.
The Confectionery Cannon is a great example of the accomplishments that dedicated students can create in three months. The team has built an incredible website to showcase the project outlining the components and design. Design requirements are met with a fun, 'because we can' attitude.
Reloading the marshmallows is my favorite part of this project. An acrylic finger allows the marshmallow to drop into the barrel and then an aluminum hatch clamps down and seals the tube. According to the website the reloading sequence takes around a second, and is faster than the regulator can recharge the pneumatic system.