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A mechanical string trimmer starter is designed in collaboration with Goodwill Industries of San Antonio, so that Goodwill can employ people with limited hand-arm dexterity who would otherwise be turned away from a string trimming (landscaping) job. The power spring based mechanical string trimmer started design includes a 6.58" x 7.08" x 7.92" aluminum box that is attachable to the rear surface of the string trimmer via a custom made aluminum attachment. The design comprises of three subsystems – the energy input, energy storage, and the energy release subsystems. The device allows the operator to compress a plunger (rack) repeatedly to store the energy in a power spring and release the accumulated energy using a ratchet mechanism. The overall design, weighing 16 lbm, requires 30-40 complete plunge compression cycles, with the force required to press the rack increasing successively as the spring charges. The maximum force of 30 lbf is required to push the plunger during the final plunge cycle. The design provides a torque of over 100 in-lbf and angular frequency of 3 total to the engine's crankshaft, sufficient to start a cold engine based on the tests performed on the Shindaiwa T272 trimmer.
Campbell, Jacob; Lavorin, Jeremy; Lovell, Tasha; Marina, Joseph; Rajbhandary, Paurakh; and Wollak, Cole, "Alternative String-Trimmer Starting Device" (2011). Engineering Senior Design Reports. 29.