Gearbox Design
In the course MECH 323: Machine Design at Queen's University, I worked with a group of students to design and prototype a shifting gearbox for both hill climb and top-speed competition events.
Collaborators: Maxime Lamadeleine, Julianna Psaltakis, Conrad Bierman, Duncan MacLaren
This project focused on designing and prototyping a custom gearbox assembly to be integrated into a pre-constructed vehicle, optimized for two conflicting events: a hill climb requiring high torque, and a top-speed run requiring high angular velocity. Because optimizing for one event reduces performance in the other, the team engineered a one-stage shifting gearbox capable of switching between gear ratios tailored for each event.
Figure 1 - SolidWorks full gearbox model
Approach
Using free-body diagrams, Python simulations, and material analysis, the team determined the torque, angular velocity, and gear ratios required for each event.
For the hill climb, the gearbox produced 4.23 Nm torque with an 11:5 gear ratio; for top speed, it achieved a 2:5 ratio, yielding an average velocity of 2.2 m/s.
Gears and shafts were designed to withstand bending and contact fatigue, with safety factors ≥1.9, indicating robust performance.
The housing was CAD-modeled and 3D-printed in ABS plastic, optimized for printing efficiency (5h 37m build time) while maintaining structural integrity.
A full assembly included 9 parts, designed to be friction-fit, with tolerances adjusted through post-processing (sanding) for smooth gear meshing.
Figure 2 - SolidWorks models of the motor (left) and shifting (right) shaft components. Indications of retaining rings, shoulders, keyways, and the 14 critical points labelled in red.
Performance & Lessons Learned
The design scored 21/24 in the evaluation matrix (theoretical) for meeting dimensional, performance, and sustainability requirements.
During actual testing, the gearbox scored 18/24, with performance limited by casing dimension errors and lower-than-expected speed outcomes.
Despite underperformance in competition, the gearbox was mechanically robust and validated the design process.
The project demonstrated the importance of trade-off analysis in engineering design, balancing torque and speed in a shifting system. Future improvements include refining tolerances, recalibrating resistance assumptions in simulations, and adjusting gear ratios for more reliable real-world performance.