Two-Stage Spur Gearbox

3.57:1overall gear ratio

Objectives

Collaborate in a five-person team to design a compact gearbox for a hill-climb vehicle
Convert the motor’s 2 N·m input torque into the torque required by the drivetrain
Design the gears and shafts for a five-year operating life with 99% reliability

Developed a two-stage, three-shaft configuration using 18-tooth pinions, 34-tooth gears, a 1.5 mm module, and a 10 mm face width
Designed stepped AISI 4130 steel shafts and evaluated shoulders, keyways, bearing seats, and retaining-ring grooves as potential failure points
Created bending-moment and torque diagrams for the input, intermediate, and output shafts
Calculated a corrected endurance limit of 336.5 MPa using Marin factors and evaluated 21 critical shaft locations using the DE-Gerber fatigue criterion
Designed a 3D-printable housing before assembling and testing the drivetrain prototype

Achieved the target 3.57:1 gear ratio and increased torque from 2 N·m at the input to 7.14 N·m at the output
Verified that every evaluated shaft location exceeded the required fatigue safety factor, with a minimum factor of safety of 1.139
Confirmed gear safety factors above 1.5 and demonstrated that the proposed gearbox was mechanically feasible
Produced and tested a functional prototype integrating the gears, shafts, bearings, and housing

PROJECT INDEX