William Gurstelle is the author of Backyard Ballistics; The Art of the Catapult; Absinthe & Flamethrowers; Building Bots; Notes from the Technology Underground; Defending Your Castle, 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 Wired, the Atlantic, and Maxim as well as other national magazines.