ME 370: Chopped!
Mechanical Design I (ME 370), a staple of the MechSE design series, focuses on introducing students to machine design from a linkage and gear train perspective while incorporating a focus on user-centered design. Every semester the course challenges students with two design projects; in the fall of 2019 students were tasked with designing and fabricating vegetable slicers.
The two projects were a hand-operated vegetable slicer and a motorized vegetable slicer. This allowed students to build off what they were learning in class, focusing on linkage design in their first iteration and then incorporating gears, cams, and other elements as they developed the motor-driven device.
Students’ machines were required to slice four different fruits and vegetables that varied in hardness, texture, and shape – banana, apple, potato, and tomato – by flipping a switch. Teams were evaluated based on the consistency of their slices as well as the safety and accessibility of their design. This project built on a project earlier in the semester where they had to design a hand-driven slicer (i.e. no switch) for people with disabilities.
Other parameters required the slicer to: fit inside a 12x10x10” box; have no load-bearing elements; be constructed from simple prototyping materials like those found in the Innovation Studio; and have no user input. Turning on a switch should feed one fruit/vegetable, slice it, and collect it in a tray without user interference. Each team’s machine had to slice each food item into at least three slices in under one minute.
“The first project had the main goal of the students learning how to design for a specific user. They also had to learn how to actually assemble a mechanism and make sure you know the work is transmitted in the right direction through the right mechanism,” said Assistant Professor Aimy Wissa. “For the second project, we asked them to think about how they could make that machine driven by a motor and gearbox and a battery. Those were big goals, but then we wanted them to be designed to be versatile enough to cut a variety of vegetables.”
The biggest challenges the students faced were with perfecting the linkage design to cut through all the items as well as find the right ratio of torque and speed for their mechanisms. Ultimately, the tomatoes caused students the most problems – even over the potato and the apple. The thick skin and soft center of the tomato were tricky for perfecting the torque requirement and necessary slicing path, but despite this many groups still were successful.
“The teams did really well,” Wissa said. “As always with any team-based work, there was a part of their effort actually going to figuring out proper team dynamics. The teams that performed the best had either worked on improving their dynamics or were lucky enough to have great team dynamics from the get-go.”
The design projects are a great opportunity for students to go above and beyond with their work. Notably, a group interviewed a chef and took video of them chopping vegetables to inform their design and another group did a difficult cam-based design to challenge themselves. The main takeaways that students get from this project are enhanced understanding of machine design, intuition on balancing torque and speed, as well as learning how to develop better team dynamics.
Professors Placid Ferreira, Elizabeth Hsiao-Wecksler, Seok Kim, and Aimy Wissa were the course instructors. Teaching Assistants included Shuvankar Goswami, Minwoong Kang, Shahriar Muhammad Nahid, and Yu Chen Xu.