The Launch: On Our Way to a Trebuchet – SCOPES-DF
Leadership Cohort

The Launch: On Our Way to a Trebuchet

An important element to any PBL (Project Based Learning) is the kickoff. This is the time to capture the interest of students  and enthusiasm for the upcoming project. What better way to launch a spring project on catapults and trebuchets than encouraging students at STEM High School in Chattanooga, Tennessee to take aim at a teacher, launching rubber balls from giant rubber tubing slingshots! The students, in groups of 4, had one chance to hit their target. They had a great time, not even realizing the collaboration and critical thinking that were taking place as groups strategized, made adjustments and encouraged other groups.

The Kick Off

“One of the ways STEM School decided to introduce the catapult PBL to us was by showing us how the Newton’s forces worked by allowing us to launch rubber balls at one of our teachers.. We used this to help us understand how to build our first catapult with pencils.” – Sky B. and Heather C.


After a successful launch, the real work began for students, but to get to this point required a well coordinated effort from content area teachers, fab lab instructors and the guidance of Fab Foundation partners. The catapult unit supports the study of quadratic functions and Newton’s Laws as students research, design and build either trebuchets or catapults. Digital fabrication is incorporated using design software, a laser cutter and a 3D carving machine or “Carvy”. The benefit of  digital fabrication is that it allows for multiple iterations in prototyping, and enables students to make adjustments to their launching device with better precision. Our ninth graders at STEM School Chattanooga had largely not had much experience using digital fabrication tools, so the challenge was to not only  create an engaging academic unit but also to provide instruction in fab tools.


“When we first began working on our catapult, we designed a prototype out of cardboard. After testing its ability, we made some minor changes in TinkerCad and then began working in the Fab Lab to carve out our second model on the Carvey. In the beginning, our design did not work out as planned because we forgot to add tabs on the pieces, causing our pieces to pop out and chip in some areas. After fixing our mistake, we reviewed our design and moved onto the laser cutter and ShopBot. Following the advice we were told, we were able to successfully cut out and assemble our final catapult before the competition. The most challenging catapult to build for us was definitely the ShopBot model, because it involved a much more complicated design program and it was much larger. Overall, this project allowed us to learn about the mechanics of catapults, different machines in the Fab Lab, and get hands on experience with designing and creating prototypes.” Grace T. and Lauren B.


Another Iteration

“The catapult PBL was my favorite of this year. I really liked the integration of the fablab and how we got to use all of the fabrication machines along with their respective design programs. My favorite was the Carvy because it was quick and easy to set up. You can use about any material you would need. One thing I didn’t like about this PBL was the fact that it was the last PBL of the year and the skills we learned could have been easily implemented in previous projects. Other than that it was great as we also got to talk to professors from MIT about our design process.” -Grant E.


This is a project that could easily be completed in a math or science class, but at STEM School Chattanooga, we embrace cross curricular PBL’s and among the  9th grade teachers our attitude is to “go big or go home”! The benefit of including all core classes in the unit is encouraging students to build connections between the math and science as well as  consider the historical purpose and construction of these devices.The culmination of the month long project was a celebratory series of challenges, where students tested their devices for accuracy and precision.


After the completion of the challenge, we brought together several student  groups for a design review discussion. Each had varying success so it was interesting to hear their perspective of the project. We have never had small group debriefs at the end of our PBL’s, but we realized the power in allowing teams to present and and provide feedback to each other in a smaller , less intimidating  setting than in a large whole group gathering.


As we celebrate the success of the unit, we have already begun reflecting in order to refine and improve the experience and student outcome. In order to capture the interest of our diverse student population, we have considered offering choice in the type of launching device. For instance, rather than just research and design a medieval trebuchet, students interested in sports could research and design a free throw  or t shirt launcher. This was a lengthy project with many moving parts, so we created a pacing guide to help students stay on track throughout each iteration.. Next year, we would add a series of challenges at each stage to ensure that students really test their prototype for accuracy and precision, and adjust their design based on the results of the challenge.

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