Inventing a Better Pumpkin Hurler

by Brian Caulfield

Some dream of going to space. Others dream of climbing distant mountains. Trey Greer just wants to throw a pumpkin a half mile with a medieval siege weapon. Greer, John Poulton, and Steve Tell, engineers in NVIDIA’s Durham, North Carolina office were one of nine teams featured in the Science Channel series “Road to the Punkin Chunkin’” in 2011.

Their edge: efficient design. Greer and his team designed their trebuchet using a home-brewed pumpkin-tossing simulator, written in Python programming language, with a little help from course notes on “constrained rigid body dynamics” by Carnegie Mellon researchers.  The computer-aided design work was then done using Google Sketch Up.

All that science makes Greer’s team a serious competitor in the annual World Championship Punkin Chunkin’ contest. The event’s competitors show up in Sussex County, Delaware, after Halloween every year wielding everything from air cannons to giant slingshots. In 2010, the team – known as “First In Fright” a play on North Carolina’s state “First in Flight” motto — placed second in the trebuchet category of the competition.

While Greer is planning on entering the Punkin Chunkin’ championship this year, his team hasn’t substantially updated its design since last year. This year it’s all about Trey’s son’s team, “Imperial Pride.” Trey’s 17-year-old son, Hastings, is about to age out of the junior bracket of the WCPC, and he wants to finish strong.  “They’ve learned to weld and got 3,000 pounds of steel,” Trey says. “It’s going to be an amazing machine.”

NVIDIA's First in Fright Team
First In Fright: Susan Poulton, NVIDIA engineer John Poulton, NVIDIA engineer Trey Greer, Susan Paulsen, Rose Hoban, and NVIDIA engineer Steve Tell.

Hastings has a knack for the tricky physics involved in translating the energy generated by dropping a 4,500 pound counterweight roughly 5 feet into 300 miles-per-hour in pumpkin velocity, Trey says.  It was Hastings who invented the ‘snapping link’ mechanism used in First In Fright’s trebuchet to amplify the pumpkin’s velocity.

Trey figures his son’s team will probably throw further than his team will this year. He even has a camera crew from the Science Channel ready to document Hasting’s efforts.

Longer term, Trey is thinking about new ways to push the pumpkin-tossing envelope. “The machines never throw so far as you’d think they’re going to, based on the simulations,” he says. The solution: get a better idea of pumpkin aerodynamics. To do that, Greer says he’ll need something special. “We’re planning on building a radar to track them using a satellite dish and some Wi-Fi transceivers,” he says.

Greer’s motto, courtesy of Dr. Seuss: “it’s fun to have fun but you have to know how.”

Image: Halloween Pumpkin by Daniele Pellati

Update: what happens when you put a bowling ball in First In Fright’s trebuchet? Watch the video, below.