Undergrads design ‘sweet’ catapults

“I think we need a higher ceiling!”

Harvard College senior Colin Saintangelo ’11, his arms outstretched, ran a victory lap around the top floor of the Hemenway Gym as his classmates cried out in astonishment.

“Forty-nine feet!”

Pole vault? Long jump? No.

Saintangelo’s four-inch-long catapult, crafted from a single piece of polycarbonate plastic, had just thrown a Tootsie Roll almost the entire length of the gym—with a ricochet off the ceiling ductwork—and launched him to the top of his class.

It was just another day in ES 51: “Computer-Aided Machine Design,” where engineering students were putting their tiny catapults to the test and competing for the longest throw.

“I made it with a very low factor of safety,” Saintangelo said, of his winning design.

“I thought it was going to break. But it was kind of like trial and error. I made three iterations, each one closer to failure. Right before it fails, that’s when it goes the farthest.”

“Next time I’ll angle it down so it doesn’t hit the ceiling,” he added.

“This assignment provides students with a hands-on design project through which they can apply the abstract concepts such as stress, strain, and stiffness that they have learned in class to the real world,” said Conor Walsh, a visiting lecturer at Harvard’s School of Engineering and Applied Sciences (SEAS), who teaches the course this semester.

The catapult project also exposes students to the methods of engineering design.

“This process involves determining design specifications, performing engineering analysis, and then iterating through prototyping and testing,” said Walsh. “Students learn that the design process is somewhat circular, so that analysis can be used to influence a design and, in turn, testing of a prototype can guide the analysis.”