Rube Goldberg Machine

Turning off a light in the most complicated way possible

For this project, my team designed and built a 10-step Rube Goldberg machine to meet the constraints of ME 270. The machine had to fit within a 30×30×30 cm cube, include both rotary and linear motion, use rigid linkages, string, and elastic components, feature at least one airborne step, and finish by turning off a battery-powered LED light.

We embraced these constraints as a challenge to design mechanisms that were not only functional but also optimized for reliability and precision. Below, I’ve highlighted some of the most technically impressive steps and the experimental analysis we performed to improve performance.

Highlighted Mechanisms

Step 1: The Cannon

The machine begins with a 3D-printed cannon that uses a rubber-band powered plunger to launch a metal marble upward into a curved ramp. This airborne step satisfied the requirement of achieving a 15 cm vertical rise while still hitting a small target with precision. Designing the ramp curvature and ensuring repeatability in launch trajectory were key engineering challenges.

Step 2: Pulley System

Triggered by a clay “parrot” weight, the pulley system transformed a simple drop into a forward push that released another marble. To ensure reliability, we designed larger pulleys with helical dividers to prevent string tangling — a small design refinement that dramatically increased system consistency.

Step 7: Four Bar Linkage

We incorporated a laser-cut acrylic four-bar linkage to transfer force between dominoes. Instead of relying on simple chain reactions, this linkage constrained motion to a predictable horizontal path, improving accuracy and showcasing mechanical design beyond basic falling objects.

Step 9: Timed Slide

The square slide was carefully designed with shallow (3°) slopes to create a step that lasted over 3 seconds — meeting the rubric’s requirement for a prolonged mechanism. Precision in angle selection was critical, as even small changes significantly affected timing.

Step 10: Mousetrap Light Switch

The finale used a mousetrap with a custom 3D-printed attachment to swing a padded wooden rod into the LED switch. The angled and padded contact surface ensured a clean strike without damaging the light, blending functionality with thoughtful engineering detail.

DOE Analysis: Optimizing the Cannon

To improve consistency of the airborne step, we conducted a Design of Experiments (DOE) analysis on the cannon. We tested three factors:

Lubrication (with or without WD-40)
Number of rubber bands (1 or 2)
Pullback distance (1 or 2 inches)

Our output variable was launch height, with a target of >15 cm while minimizing variance.

Key Findings:

Lubrication had negligible effect.
Rubber band count was the dominant factor — increasing from 1 to 2 bands created a large step change in launch height.
Pullback distance had a smaller, more tunable effect, useful for fine adjustments.

Optimized Settings:

1 rubber band, pulled back 2 inches gave the most consistent launches above 15 cm

This experiment not only satisfied the DOE requirement of the course but also reinforced how structured testing can guide design improvements in a hands-on engineering context.

Key Takeaways

Building this machine was more than just about creativity — it demanded precision in CAD modeling, tolerance analysis, and iterative testing. The DOE study in particular highlighted the importance of data-driven decision-making in design optimization. Our machine successfully combined mechanical ingenuity with analytical rigor to meet all constraints and reliably achieve its goal.

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