Sizing the Components of Existing Machinery to Gradually Develop Machine Design Expertise

Typical design (sizing) projects in a Machine Design course tend to rely on abstractions of the machine; that is, situations in which the student must imagine the system, perhaps with the aid of a 2D schematic, and conduct the sizing calculations in a completely theoretical and abstract fashion. This skill is certainly a requirement of an experienced machine designer; however, novices may be outmatched when exposed to this level of expertise at an early stage in their development. This article suggests that the sizing projects should be based on existing machinery that is available in the university, and that is accessible for inspection and exploration by students. The sizing results are then compared to the existing machine to determine the reasonableness of the calculations. This approach “conditionalizes” knowledge and provides students with an intermediate design experience before undertaking a major machine design experience in their capstone course. Furthermore, based on the “backwards design” planning framework for designing courses, the paper suggests that the project should be approached gradually – in phases – from the first day of class, and extending throughout the semester, to provide quality feedback to students throughout the entire process, thus increasing the potential of achieving expertise. The phases were also synchronized with the material presented in class, and with the exams, to further strengthen the knowledge acquired by the students. The project specifically addressed the sizing of components of an existing SAE Baja race car gearbox (size the shafts, keys, gears, and bearings). Phases 1 and 2 of the project asked students to calculate/estimate the external loads acting on the input and output shafts of the gearbox. In these first two phases students were able to start experiencing a typical real-world situation in which, unlike textbook problems, the loads acting on the system were unknown and had to be determined. It required searching the internet, consulting textbooks, inspecting the Baja, and making assumptions. In the last phases, the students compared the results of their sizing calculations to the existing components and applied critical thinking skills (discern the true from the false and be able to explain it) to explain differences in the sizes of the components. This study is based on the literature on expertise, and the learning processes that support its development. A survey of skills, given as a preand post-survey to students, validates the strength of using this scheme. The survey results were further validated by direct assessment of the written reports.