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This report outlines the overview of our final cart design and evaluates the design’s compliance to the project requirements, constraints, and objectives. This report also includes recommendations, future improvements and tests that to be completed after the shelter-in-place order has been rescinded in Bexar County.
Our final design saves 10.41 lbs in Fusion 360. This means that we met the major requirement of our design since the cart is 10% to 20% lighter than the original reference cart weight of 100 lbs. Our design changes include reducing the gauge of some of the parts of the cart (the main beam and gooseneck of the chassis and the handlebars). Additionally we reduced the amount of wood on the basket and chair by reducing the width or thickness of some parts or removing non-load bearing portions that withstood our loading conditions in simulations and physical testing. The major design changes include changing from a wood to a fabric chair back as well as going from a rigid wood trailer to a lighter, removable trailer on the basket. A full discussion of our design changes with pictures can be seen later in the report.
In this report, we analysed our test results to determine how well the final design met the requirements. We conducted finite element simulations that evaluated the cart’s four subsystems, tractor, chassis, basket, and chair, as well as the whole cart. The physical tests for the first prototype are discussed and the simulation results for the final prototype. Due to the COVID-19 shelter-in-place order, the Cartologists were unable to physically test the final prototype. However, based on the results from the physical testing for the first prototype and Fusion 360 simulation results for the final prototype, we were able to confidently meet the majority of our requirements. The only requirement and constraint that was not met was that the cart should cost no more than the reference cart (~$300). The final prototype has a projected cost 1.2% higher than the reference cart. However, our sponsor at Mobility Worldwide indicated that a slight cost increase is acceptable as long as it reduces weight, and/or adds a valuable feature. Additionally, the cost estimate could be lower depending on discounts from buying in bulk or from local suppliers.
We will also provide Mobility Worldwide a drawing package of our final design. With it they can build and evaluate the final prototype. Additionally, future work should include building, testing and evaluating our two options for the basket trailer, which secures items in the back of the cart, described in detail in Appendix C. The two methods are a slidable plate, or a net/fabric mesh. Both methods are presented in the report for Mobility Worldwide’s evaluation and final consideration.
Mielke, Sam; Rafferty, Hanna; and Wellford, Anne, "Final Project Report for a Lighter Mobility Cart" (2020). Engineering Senior Design Reports. 39.