If you want to crash a local parade of human-powered vehicles and soak unsuspecting onlookers in water or vaporized hot dogs, a pink camouflage tank is a pretty good craft to do it in. At least that's what 30-year-old Philadelphia gearhead Vin Marshall thought when he persuaded nine of his friends to build the 2,000-pound replica, complete with a functioning pneumatic cannon.

Martin Montesano had been captivated since childhood by enormous walking machines like the ones in The Empire Strikes Back. A few real-life versions have been built before, but they never lived up to his vision. He wanted his to be huge.

Playing the harp isn’t the most high-tech pastime—unless, like Stephen Hobley, you use lasers in place of the strings. Though not the first home-built laser harp, Hobley’s creation is unquestionably the coolest. Played by disrupting the laser beams with his hands, it can produce just about any sound. Better yet, it’s also a fully functioning controller for a version of Guitar Hero.

Stuntman Ray Baumann is accustomed to vehicles that soar through the air, vaulting over rows of cars. But the Australian’s latest ride makes its bones on the ground. It’s the Monster Motorbike from Hell, a 10-foot-tall, 15-ton beast that drags vans around racetracks and flattens sedans as if they were soda cans.

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I admit it: Im completely addicted to Battlestar Galactica. And after watching countless episodes, I was convinced I could bank and spin a Viper, the shows signature spaceship, like a pro. So to prove it, some friends and I built a full-cockpit flight simulator to enable total immersion in the BSG universe.

Citizens of Philadelphia, beware: You may see a grown man whizzing by you on a skateboard, doing 20 mph. That would be PopSci staff photographer John Carnett, and in case you dont get a good look, its a souped-up, motorized board he built from the ground up.