Title of case study	Project-based Learning (the trebuchet project)
School/Subject:	CoSE/Mechanical Engineering
Lecturer(s):	Paul Prentice
Course:	Engineering Skills 1 (ENG1026)
Student Level:	1st year UG
Class size:	150
Location:	Online / distance (students work in groups in their own time) & on campus/in person (students present the final product in person)

 

Brief summary

First year engineering students individually virtually designed a prototype of a trebuchet, for presenting and receiving feedback. Within groups, students combined the best elements of their individual trebuchets to develop a group design. These were ‘nested’ for laser-cutting, and physical models constructed, for testing and optimizing. A shoot-off competition identified the champion trebuchet (range and accuracy), and students submitted individual reports (which had to include an analysis component).

 

Objectives

The first year Engineering Skills Design Build & Test exercise was the first significant student-led project that our students encountered on their degree program. It may also have been the first time they design a complex object in Autodesk Fusion (Computer Aided Drawing), as an essential engineering skill, and perhaps the first time they’ve been given an open-ended opportunity to research and develop a model (without following instructions or a manual).

Other intended learning outcomes associated with the project include design for laser-cutting, consideration of tolerances and assembly practice (problem solving and ‘bodging’ it, when necessary), working within material constraints (compressed cardboard), team working, and scientific report writing (often a first experience).

For me, the selection of the ‘target object’ for a project such as this was critical. It should be something relatable/accessible and engaging, but represent a genuine design challenge, whilst also having scope for real engineering analysis (appropriate to first year engineering students). The trebuchet fits these requirements very well, with the added advantage of being readily tested in a competition-style scenario.

 

What is done?

In terms of teaching methods, the individual presentations were a flipped classroom approach, with students presenting their own research-based designs and receiving feedback. This was also an opportunity to emphasise some key principles, for example, first and foremost, would the design be a functioning trebuchet (and if not, why not)? The limitations of the build-material they will be using for the team and physical build phases of the project; how can these limitations be mitigated via engineering of the designs? What about the sling component, (which isn’t suited to designing, in Fusion) and counterweight material? Can an analysis component be planned for and incorporated into the design?

The students were put into groups of three or four, but no more than that to ensure no freeriding issues could hinder the students’ chances at being successful. Firstly, the students were tasked with creating a group trebuchet in the Autodesk Fusion program, while using the help of the CAD support team if needed. After finishing their design in the program and usually a week before the submission required it, the students would send the model and its parts to the demonstrator to check it for any major issues. The demonstrator then laser-cut the parts for the groups, leaving the students to assemble their model themselves. The students would use various methods, like drilling and filing, to not only assemble the model, but also to test whether it conforms to the predefined criteria. This initial build-in session took place in labs with workshop facilities, after which the students again worked on further building and testing within their own groups, in their free time. The main scoring deliverable was the individual report, which were marked by the demonstrators and moderated by the lecturer. The assembled trebuchets were finally tested in the competition itself, with the first team winning a laser-cut trophy, designed by the CAD support team.

The project involved CAD technical support team for Autodesk Fusion, and up to six EWF (Extended Work Force) demonstrators for mentoring, laser cutting, running the build sessions and report marking. The only material used for the trebuchets was cardboard, with each team allocated four sheets. This has proved to be an excellent build material choice for its cheapness, accessibility and added challenge to the students of make the trebuchet resilient and robust. All these supplies and resources were supplied by the University.

 

What works well?

The choice of the trebuchet; there are many (many!) YouTube clips of enthusiasts building, testing and optimising every conceivable type of trebuchet. There is also a small body of scientific literature available on the topic, so students could access ‘research–style’ journal papers and scientific knowledge, methods and maths. There are so many options for analysis and different directions to explore for optimising performance, so students could also experience ‘scientific method’ (logic-based processes, statistical significance, treating experimental uncertainties, etc.).

For the first couple of years, the project was run with Perspex as the primary build material. During COVID however, Perspex became hard to source as it was under demand for screens and personal protective equipment, and so we switched to compressed cardboard. This was a more challenging material to build a dynamic, fast-moving and energetic structure from with less inertia meaning stability was an issue, and parts subject to strain during operation requiring reinforcement. Of course, cardboard was also more sustainable (and cheaper!) than Perspex, which could be impressed upon the students.

 

Benefits

Students

Staff

It is a fun project for them, particularly the competition time. The students are already doing engineering in their first year, as they have to figure out the measurements, weights and physics of the trebuchet to work efficiently. Such project-based learning is core to what engineering truly is in practice. Students get support in the materials they are offered, for instance, YouTube video guides, articles, blogs, CAD support for the Fusion program and feedback from the lecturer. The project itself is also a test of the students’ creativity. The Fusion program and its use in the project is a highly valuable skill, because the program is a well-known and popular one in the field of engineering. The team that wins receives a prize, making them more motivated to complete the trebuchet efficiently, and the winning team can also put their win on a CV or LinkedIn. It is beneficial that the students don’t know each other beforehand, because they all feel more motivated to contribute to the group. If some members of a group don’t work together efficiently, the ones voicing their concerns are given the option to join other teams or to work on the project on their own.

This method of learning is very enjoyable for the lecturer as well. Thanks to the queries the students send to the lecturer, and the competition itself, this leads to an element of bonding between the lecturer and the students. This is very important if the lecturer is in an advisory position, as the students can recognise them and feel more at ease in trusting them about their issues.

 

Challenges            

Students

Staff

In the groups, sometimes one student takes the lead and doesn’t let others to be equally as active. There is the potential for freeriding by some students, which is also difficult to ascertain as the students work on the project outside the contact hours. Though if students report this issue, they are given the choice to join another group or keep working on their own. Some students might have difficulties understanding and mastering the Fusion program, but they have access to technicians from CAD if needed. Also, they have to learn how to operate Fusion as a key program of their degree.

As the lecturer responds to the students’ emails and queries alone, it can be quite time-consuming as each group have their own issues needing addressed.

 

What did you learn?

It would be amazing if students were able to construct full-scale trebuchets. However, the resources and skills needed for this are beyond the scope of a first-year project, (maybe as a final year project!?).

Although cardboard as the build material works well, as described previously, it does rule out a number of advanced trebuchet designs. The ‘violent’ action of the flywheel or murlin trebuchets, for example, means they’re not really feasible.

Another important thing to remember is that course coordinators should not change too often, if such project-based learning method is to succeed. It takes a few years (at least) to get the projects running smoothly – and there’s always room for further improvements!

 

What advice would you give to others?

I would want to first point out that this particular course/project offers possibly unique scope to select a topic that is likely to appeal to students, whilst meeting the engineering skills intended learning outcomes. There’s a freedom associated with this project that isn’t available with engineering maths, for example, or other core technical courses on the programme.

And it’s hardly a revelation to suggest that student-engagement is fundamental to the successful delivery of any course – and this one more than most. Students need (and are expected to) invest their own time into every phase of the project (individual and team designs, finishing the build and optimising performance). I think the shoot-off competitions work well for motivating students not to fail and/or compel them to produce the best performing trebuchet they can.

More generally, I don’t allow myself to think of any of the courses I teach as complete/finished. Even if it’s not new content; something updated, a new demo, online resource. Courses should be living evolving things, including this one. This year, all teams will be using blue-tack balls as projectiles, and I’ll be making dart-board style targets. An easily changed projectile mass could also be a great analysis topic.