Though this silent shooter throbs with electric power, it’s based on just about the oldest ballistic principle on record—the one that helped David clobber Goliath with a sling: pick up a missile, spin it to gather force, then let go. Wham!
Not that this cannon is any giant-killer. We kept it small to be on the safer side. But it’s a great demonstration of centrifugal power, and it’ll shoot a BB 25 or 30 feet at a muzzle velocity of around 25 feet per second. This may set you thinking of the potential of a centrifugal gun whirled by a gas turbine at, say, 20,000 r.p.m. With an effective wing radius of about 6 in., you’d get a muzzle velocity of over 5000 f.p.s.— better than a high-powered rifle!
The spin mechanism is simple and cheap to build. The toy motor is mounted by soldering its lugs or bushing (or both) into a hole in the bottom of a cellophane-tape can. The rotor that’s spun by the motor shaft consists of a base plate to which is soldered a short tube, bent and slotted to allow free passage of the BB shot. This unit must turn without binding; the pickup spike must pass freely through the end slot. Bevel the opposite end of the tube flush with the top of the can cover.
The end of the magazine tube is undercut and bent so the dropping BB enters cleanly into the whirling pick-up tube. A large paper clip provides wire for the trigger. Pulling back on it releases one shot while blocking the others. This lets the rotor recover its speed between shots.