Single Stage Gearbox

This is the final project of my Machine Design course. We were required to design a gearbox for an aircraft propeller and perform stress and fatigue analyses. I performed most of the technical work and led my team to achieve the top score in the class of 93%.

The gearbox was designed to be coupled to a 10 hp motor which operated between 1000-3000 rpm. It was required to have a 1:3 ratio, withstand torques up to 50 lbf-ft, withstand thrust loads up to 75 lbf, have at least a 1.8 safety factor, and operate for greater than 10^7 cycles. The gearbox consists of a spur gear and pinion, their respective stepped shafts, four ball bearings, retaining rings to locate the gears, and the outer housing.

The gears were custom designed for this application using an iterative approach to satisfy the desired safety factor, load, and lifespan requirements. I developed a MATLAB program, which also used an iterative approach, to determine the optimal location and diameter for the shaft steps. The program would start with a given material and generate a shaft with the minimum diameters to prevent yielding. The newly generated shaft would then be tested for the factor of safety at each critical location (each shaft step and key slot). If the test failed, then the diameter would be incremented to the next standard size and the process would repeat. Of course, the shafts could have been designed using shaft design tools in CAD software, but it was interesting to develop a better understanding of what goes on behind the scenes.