William Gurstelle is the author of Absinthe & Flamethrowers; The Art of the Catapult; Backyard Ballistics; Building Bots; Notes from the Technology Underground; and Whoosh, Boom, Splat. He is a professional engineer who has been researching and building model catapults and ballistic devices for more than 30 years and is a contributing editor at Popular Mechanics, a columnist for Make magazine, and writes frequently for the Atlantic, Maxim, and Wired as well as other national magazines. He lives in Minneapolis, Minnesota.