An Excel-based approach for designing stepped driveshafts for mobility devices and a study of its use in a design of machine elements course

The aim of this paper is to describe a new MS Excel-based approach for designing driveshafts for stiffness and fatigue strength. We analyze the efficacy of the approach in engaging students in an iterative design process and higher-level qualitative decision-making activities in an undergraduate class at Texas A&M University. Compared to conventional fixed cross-section frames and trusses, there are few tools (barring Finite Element Packages) that facilitate rapid design evaluations of stepped shafts. The approach is based on a novel use of singularity functions to obtain explicit solutions for stepped shafts under concentrated loads. This approach allows for relatively easy implementation into Excel without the need for any numerical integration or other forms of approximation. Currently, the tedious calculations involved in the design of stepped shafts prevent instructors from exploring iterative changes in driveshaft design. The Excel tool that we have developed allows instructors and students to focus on iterative decision-making. With this tool, open-ended design questions are assigned even in exams since the entire iterative process takes less than 15-20 min. Student surveys and analysis of exam answers reveal that students have gained a considerable capability to make design decisions. They also indicate areas where improvement in design thinking is needed.