Boxer Engine (Movement 93) — Ethan Liao & Justin Xia

Concept and Ideation

We began with the idea of building a V-shaped engine. After reviewing previous EDES 210 projects, we realized that engine designs were common, especially V-type ones. To make ours distinct while still staying true to 507 Mechanical Movements, we pivoted toward a boxer engine—a horizontally opposed configuration that uses Movement #93 (Scotch Yoke) to convert rotary motion into linear motion.

We sketched out how each piston would translate back and forth along the same axis, using two mirrored Scotch Yoke mechanisms on either side of a central crank. This early sketch phase helped us visualize how to mount the pistons, attach the crank, and keep the mechanism balanced.

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Gate 1 — Sketching and Cardboard Model

Our first step was creating simple 2D drawings of the Scotch Yoke and piston arrangement in Adobe Illustrator. We iterated on the slot shape that would guide the piston movement and the circular cam that would drive it.

We cut a cardboard model to test clearances and overall motion. The model moved but showed us that the friction points and alignment tolerance would be critical when we switched to wood. This low-fidelity prototype confirmed that the Scotch Yoke movement was smooth enough to scale up.

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Gate 2 — Laser-Cut Wooden Mechanism

We cut our medium-fidelity wooden parts from OEDK plywood sheets. These included:

• The main face plates and base

• The circular cam and oval ring

• The sliding yoke and piston slots

Once assembled, the laser-cut mechanism produced even, smooth motion. We tested rotation and piston stroke by hand-turning a temporary handle. We realized that tight tolerances in wood increased friction, so later versions sanded the moving pieces more aggressively and slightly enlarged the oval track to reduce sticking.

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Gate 3 — Sliding-Lid Enclosure

Next, we built a box housing with a sliding lid to enclose the mechanism. The lid fit tightly to keep the structure aligned but had to be laser-cut multiple times to achieve proper clearances. This stage focused on aesthetic and structural integration—how to make the mechanism both functional and visually cohesive.

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Final Build — Finishing and Aesthetics

For the final model, we focused on both function and finish:

• Engraved Designs — We added line engravings and laser-etched patterns to make the box look like a race-car engine, matching the “boxer” concept.

• Vinyl Cut Decals — We cut and applied 12 in² of vinyl in racing-stripe patterns.

• Wooden Pistons — Each moving piece had wooden piston heads glued to the dowel ends to simulate real pistons.

• Metal Handles — We water-jet-cut ¼-inch aluminum handle pieces, sandblasted them for texture, and epoxy-bonded them to the dowel shafts. These handles allow users to rotate the engine manually.

After final sanding and assembly, the motion was consistent across both sides—each piston moved smoothly in opposite directions, producing the distinctive even motion of a real boxer engine.

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Challenges

• Box Fitting: We had to re-laser-cut parts several times because early box dimensions were slightly off from the moving mechanism’s width.

• Friction: The wooden Scotch Yoke required fine sanding and small geometry tweaks. We widened the slot and rounded the cam edges to reduce sticking. If we were to redo the project, we would put the dowels in bearings to make the rotations even smoother.

• Tolerance Alignment: Wood flex and moisture variation made tight fits unreliable, so we loosened tolerances for smoother operation.

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Workspace and Cleanup

We cleaned and reset our workspace after finishing the final assembly, keeping the OEDK tables clear for the next project cycle.

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Cost Breakdown

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Reflection

The final product successfully demonstrated the even, opposing motion that defines a boxer engine. The Scotch Yoke mechanism worked as intended, and the combination of wood, vinyl, and aluminum gave it both mechanical function and polished aesthetics. The project balanced technical precision with creative detailing, producing a model that’s satisfying to use and visually engaging.