No Batteries Required

Winter 2009

On a Friday afternoon in early December, students in Allison Okamura’s Mechanical Engineering Freshman Laboratory, working in teams of three, wound string around wooden dowels, carved foamcore with X-Acto knives, and cut pieces of balsa and plywood.

Their assignment—building a vehicle powered only by two mousetraps and six rubber bands—is the culminating project in the fall semester’s introductory mechanical engineering lab. “The mousetrap-and-rubber-band car is a classic design assignment,” Okamura says. “What makes this project interesting are the twists I’ve added.”

The “twists” can be found in the assignment’s 27 rules which, along with weight and size restrictions and a prohibition on pre-manufactured assemblies (not parts), state that the cars, when competing in a single-elimination tournament, must slalom between two two-liter soda bottles. And, as they traverse the 11-foot-long, paper-covered course, they must also lay down a continuous line from the start to finish gates. “It’s usually the most mundane things that cause the greatest frustrations,” Okamura says.

Konstantinos Bertsatos and team have stripped the wheels and axels from a toy all-terrain vehicle. The four tires sit on the lab table as Bertsatos removes auto parts from a plastic storage container. There’s a Liquid Glitter eyeliner in Starlit Black (“The package says it will make a continuous line,” Bertsatos states, looking at the tube skeptically), a red plastic Nathan’s Hot Dog fork, two CDs, a few pieces of bent aluminum, and the regulation mousetraps and rubberbands. The car, Flash Gordon, though unassembled, is predicted to be a strong contender by Jason Glasser, a first-year grad student and the lab’s teaching assistant. “It’s a great design,” Glasser says, “I especially like that they’re tilting the axel because it takes advantage of the geometry of the situation.”

On the following Monday afternoon, though, neither the tilted axel nor the Sharpie marker (which replaced the eyeliner) really mattered. Eighteen inches into the course, a piece of string wrapped around a dowel caught on the car’s frame and Flash Gordon never made it to the first soda bottle.

Last One Done, a car that Glasser thought had potential if the students could resolve some steering problems, at first appeared to work beautifully. The crowd cheered as the car, the first to successfully maneuver through the course, crossed the finish line. In the starting line excitement, though, the magic marker’s cap hadn’t been removed. No line was drawn so Last One Done was eliminated.

The winner turned out to be Awesome-O. The secret to the car’s success? Team member Nicholas Salzman explains, “We built our own practice course, calibrated the car again and again and again, and knew exactly how we needed to angle it. That’s how we did it.”