All projects Project 02 · Mechanical design

SUBC Submarine Drivetrain

The human-powered drivetrain for UBC's competition submarine, with 37% lighter side plates and no more slippage on the driving pinion.

Team: SUBC, UBC Submarine Design Team
Timeline: 2025 - 2026
My role: Drivetrain Engineer
Outcome: 37% lighter side plates

interactive gearbox assembly

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Longer, in-depth explanation Flip the switch for the full engineering breakdown

Quick explanation

What it is

SUBC builds human-powered submarines to race internationally. A diver inside pedals the sub through a course.
I work on the drivetrain: a 2:1 straight-bevel gearbox that turns pedalling into propeller rotation, designed for a 1.8–2.1 kN load.
FEA-guided material removal cut the side plates from 1.89 lb to 1.19 lb (37%), and a modified step-down collar stopped the driving pinion from slipping.
Modelled in SolidWorks, validated with FEA, and CNC machined in-house.

Deep dive

How the drivetrain came together

Part 1: the problem

1. Two things were wrong with the old gearbox

It was heavier than it needed to be. The whole vehicle is buoyancy-balanced, so every gram of structure is a gram that has to be offset somewhere else.
The driving pinion slipped on its shaft and drifted out of alignment, losing power at exactly the moment the pilot was pushing hardest.
Both problems lived in the same two components: the side plates that carry the bearing bores, and the collar that locates the driving pinion.

Part 2: concept & CAD

2. Generating and narrowing the side plate concepts

Generated several side plate concepts and scored them against weight, stiffness, and, critically, whether a machinist could actually fixture and cut them.
Modelled the shortlist in SolidWorks, iterating the geometry around the bearing bores and mounting interfaces where the loads concentrate.
Kept the bearing seats as the fixed reference and let everything else move, so alignment stayed correct through every revision.

Part 3: FEA optimization

3. Letting the analysis remove the material

Ran FEA on each iteration against the 1.8–2.1 kN design load and removed material from the low-stress regions the analysis highlighted.
Held the required safety factors as the hard constraint, and got the side plates from 1.89 lb down to 1.19 lb, 37% lighter.
Several concepts I liked visually didn't hold the safety factor and had to be thrown out. This was the first project where FEA changed my design rather than just confirming it.

Part 4: fixing the slippage

4. Turning a stock collar into a step-down collar

The driving pinion was slipping on its shaft and losing alignment, and nothing off the shelf fit the jump from 0.500 in to 0.375 in.
Modified a stock McMaster-Carr shaft collar into a 0.500 to 0.375 in step-down collar in SolidWorks, sized for our gearbox and for what we could machine in-house.
Made drawings so the fits were unambiguous to whoever cut the part.

Part 5: manufacturing & results

5. Cutting it and proving it

Prepared drawings for CNC machining, then installed the finished side plates into the assembly.
37% lighter side plates (1.89 → 1.19 lb) while holding the required safety factors.
Pinion slippage eliminated and alignment restored with the step-down collar.

The biggest lesson wasn't the analysis. It was how much manufacturing constrains design. Designing around what we could machine in-house changed my geometry more than any simulation did, because a part you can't fixture is a part you can't make.