The Induction Gun

This is a device that launches 2 inch long bolts of metal without moving, touching them, or making a sound.

This has been a pet project of mine for a while. The concept is that a hollow coil of wire can be energized to attract a bolt of metal towards its center, and then turned off before the it gets there so that it will continue through the center of the coil and out the other side. One coil wasn't powerful enough, so I hooked up two more coils with infrared light gates before them. A simple tunable RC delay allowed me to optimize coil timing.

So you also need some way to get a large amount of current flowing through the coils in a short time. I showed up at MotoPhoto and asked them for all the disposable camera shells they had and they happily obliged me. Inside each one is a circuit that charges a 160 uF capacitor to about 320V. I upped the capacitance by adding a few more in parallel, and then used 800V SCR's to discharge them. I predict well over 50 amps peak current.

I also built a little circuit that would time how long the projectile broke a final infrared beam. This was an easy way to calculate muzzle velocity, which was about 25 ft/sec. It's enough to shove a blunt piece of steel all the way through the side of a corrugated cardboard box, though.

A little side note, 300V shocks actually kind of tickle.

A nice shot of the gun.
A closeup of the coils. There's no need for a barrel, because the projectile floats down the center of the coils. It's also completely silent.
You can see the 3 camera circuits at the bottom of this picture
A scar on my professor's desk that may or may not have been caused by a bolt accidentally shot from the other side of the lab late at night.