Centrifugal Marble Cannon

Posted by on May 12, 2008 in Blog | Comments Off

Centrifugal Marble Cannon

How often do you get to use the words ‘Centrifugal Marble Cannon’ in a sentence? Here’s the 411.

About 6 months ago, the Make blog posed a scan from a 1963 Modern Mechanics magazine that detailed the fabrication of a cute little electric BB gun that used centrifugal force to accelerate the projectiles. Here’s how old I am:

I clearly remember reading the article in the magazine when it was originally published.

In 1963.

45 freakin’ years ago.
How cool is that?

Anyway, I loved the concept when I first saw it, and seeing the mechanism again kindled a thin, yet white hot flame of inspiration. So I scoped out the plans, redesigned the impeller assembly, simplified the trigger mechanism and chucked the barrel into the dustbin.

Then scaled it up by about 300%. The projectile of choice? Yer standard 5/8″ diameter glass marble. The motor? A surprisingly torquey 6000 RPM 1/15 hp jobbie I liberated from an early ’70′s Sears sewing Machine. I prototyped the design using a 7 1/4″ Super 8 movie film canister as the spin chamber and was firing about 250 feet with a muzzle velocity of about 100 fps. The piece you see here is has a spin chamber 8 1/4″ diameter, and while the range hasn’t improved, muzzle velocity is currently hovering in the 145-148 fps range, with a rate of fire of about 100 rounds per minute.

The performance is…gratifying.

This particular piece weighs a shade over 13 pounds, and is done in brass and copper. The spinchamber walls are lined with3 ply birch finished with an industrial strength layer of carnauba wax for friction reduction..

It’s equipped with a laser sight, geared trigger mechanism and a rock steady worm gear tilt mechanism. The magazine is likely good for about 200 rounds, and the whole thing spins on a tripod base which had previously enjoyed a long and dignified career in academia, serving as a retrort stand in the BC chemistry department.

It is a quiite startling mechanism, no shit.

Here’s some more pictures…

i’ll shoot some video later today.

$1600, shipping included.