Machine Design Project
Overview
This was a final project that tested for the ability to develop the fundamental physics from 1st law principals, design a gearbox, and perform a fatigue analysis.
Project Goals & Guidelines
The main goal of the project was to design a gearbox for use in low-speed vehicles (LSV) using two-motor architecture. The physics for the problem was developed and analyzed at the motor's peak power and peak speed. The motor that was used for this project had a peak power of 40hp at 4400 RPM, with a maximum speed of 7200 RPM. It was also assumed that the average platform mass of the vehicle would be 1500lbs.
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The specific goal of the gearbox was to enhance the motors to allow the vehicle to travel up to 35 mph on a flat surface while reaching top speed in less than 6 seconds and maintaining speed on a 25% grade.
Physics
The physics was the foundation for the project. First, a free-body diagram was created in order to visualize all the forces acting on the LSV. Once the forces were accounted for, they each needed to be individually solved. The general process for this is shown below. The only unknown in this energy balance was the motor force, which was solved for in order to get the required gear ratio.
Gearbox Design
Below is the final gear design. Although a compound reverted gear train was considered, a planetary gear system was chosen due to its compact nature. The gear train design consisted of avoiding interference, minimizing dimensions, and producing the required torque while continuing to meet the minimum speed for the LSV.
Fatigue Analysis
Since the shaft that connects the input motor to the gearbox will be frequently applying high torques, it was important to perform a fatigue analysis on the shaft. The failure theory of ASME Elliptic was used alongside the Marin equation in order to complete the fatigue analysis and design a shaft for infinite life.