MechanicalMar 2026
Two-Stage Spur Gearbox Design
Kinematic Analysis Lead — MECH3110 Group Project
A group machine design project at UNSW to design replacement gears for a broken gearbox synchronising a motorised bridge with a free-rolling cart. The cart reaches the gap in 1.425 seconds on a 15° ramp. Once both start moving, neither can stop, so the bridge had to be in position first try.
- Led kinematic analysis: back-solved from cart timing to fix required bridge speed at 118.67 mm/s and target gear ratio at 1.417
- Searched 733 integer tooth combinations to find counts satisfying the ratio within the centre-distance constraint and landed on 54/46 and 70/58
- Verified all four gears against AGMA bending and contact stress limits; Gear 5 bending was tightest at 11.4% below allowable, justified against the 1.2 design factor
- Shaft fatigue FOS of 5.5 at critical shoulder; undercut fillet reduced stress concentration factor from 2.2 to 1.8
Tech Stack
AGMA Gear AnalysisSolidWorksKinematic SynthesisShaft Fatigue AnalysisGeometric Tolerancing
Gallery
Challenges
- Finding integer tooth counts across 733 combinations that satisfy both the gear ratio and geometric constraints
- Specifying shaft tolerances, surface finish, and fillet radii to meet SKF bearing requirements and preserve fatigue strength
- Identifying Gear 5 bending as the critical margin and justifying the design factor
Outcomes
- Gear ratio of 1.417 achieved with 54/46 and 70/58 tooth combinations across two stages
- All four gears pass AGMA bending and contact stress checks with design factor of 1.2
- Shaft fatigue FOS of 5.5 at critical shoulder; undercut fillet reduced stress concentration factor from 2.2 to 1.8