Flying Pumpkins

NCC physics students know how to sling 'em

Kim de Bourbon; photos by Kim and Charles de Bourbon and Marianne Atherton,

The science and the construction proved reliable as a team of Northampton Community College students tackled a project of unusual fun this fall: Using physics principles to power a pumpkin across the plains of the Pocono Plateau.

The occasion was the Last Fling Pumpkin Sling held October 18 and 19 at Pocono Raceway.

The challenge to build a pumpkin-tossing machine for the event came from Dr. Matt Connell, dean of NCC's Monroe campus. He gave a flier and a $250 budget to physics instructor Miles Harris.

"I've never seen students so excited as when I came to class and said 'Who wants to sling a pumpkin?'" Harris said. There wasn't much time -- the machine had to be designed, built and tested in three weeks.

The competition features four different classes of machines, all strictly mechanical. The group decided to build a type of catapult that was used as a weapon in the Middle Ages. It is powered only by counterweights.

"We decided on the short-arm trebuchet class," Harris said. "It was simpler and easier to build."

Nick Chiumento was the lead designer, finding photos of a machine online and sketching out a blueprint using SketchUp Make, a free 3D drawing program.

Along with Nick, Andy Atherton, Rob Fischetti, Jeff Lisk, Kimberly Maricle and Brian Wojcik spent the two weekends constructing the trebuchet out of pressure-treated 4x4 posts and plywood, putting in 77 combined hours of work.

"I was very hands-off," Harris said, other than providing his backyard for the project construction site. "The students did the bulk of the work."

The concept is simple, but the execution tricky: A long "throw arm" pivoting on a fulcrum is mounted on a stand. At the short end of the arm, attach the heaviest weights you can find, and raise that end in the air. At the long end of the arm, attach a rope with a sling at the end to hold the ammunition - a 2- to 4-pound pumpkin. Drop the weighted end, and energy is transferred to whip the long end around and fling the pumpkin.

For a counterweight the NCC team used a wooden box filled with rocks and dirt, topped with two 7-pound dumbbells, two 25-pound barbell weights, and a 60-pound bag of sand. All told, about 150 pounds on the business end of their trebuchet.

At the tossing end of the arm is a release pin made from the leg of a camp chair, lengths of nylon parachute cord, and the seat of the same camp chair, used as the pumpkin-holding sling.

In tests after construction the team estimated their best toss at about 60 feet. At the Pumpkin Sling, their throws got increasingly better: 65 feet in the practice round, followed by 71, 77 and finally 87 feet in the three official rounds.

Bigger machines that use springs or other forms of tension can toss a pumpkin thousands of feet. But for quick, consistent and reliable shots, the NCC trebuchet was a proven winner.

And it wasn't an easy day to be slinging pumpkins. As the competition began Sunday morning on the open fields outside the racetrack, contestants and spectators - most not dressed for wintry weather - were enduring 20 mph winds that made the 38-degree temperature feel like 28. Machines were throwing into the wind, shortening the distances of the tosses.

What changes might be made next year, when NCC plans to return to the contest? The team spent a lot of time looking over other machines for ideas.

"We've been talking about making it taller, so the weights can fall farther, and give us more distance," Harris said. "Ideally, the throwing arm is vertical when it releases the load."

They also would like to incorporate a way to easily adjust the angle of the toss, and to make the machine even sturdier, so they can use more weight. (The team added 50 pounds before their final toss, stretching links in the chains holding the counterweight box.)

Harris said they hope to demonstrate the trebuchet on campus, perhaps at community events. He would also like to incorporate it in the college's SMaRT program that encourages young children to pursue interests in science, math and related technology.

Check out more photos in this Flickr gallery. To see the pumpkin-slinging action, check out this YouTube video.