[The following article and photographs are by a contributor who prefers to remain anonymous, and appear through the courtesy of the author/photographer and are Copyright © 1998 by the author/photographer.]
The Gravitram rolling ball sculpture (RBS) is located in the lobby of the OMSI (Oregon Museum of Science and Industry) in Portland, Oregon. The placard reads -- "Gravitram was created by Shabtay Levy and George Hohnstein September 20, 1973." It is fascinating for all ages.
The Gravitram is about 10 feet high and 5 feet square at its base. Compared to many RBS, it is very dense in appearance. The tracks are relatively small and positioned close together. If you stand back and observe many RBS, one can study the various potential ball paths. This is almost impossible with the Gravitram due to its density. On first glance, it appears to be a rather chaotic jumble of wire.
The tracks are constructed of brazed rod that looks about twice the thickness of a coat hanger with an apparently high copper content, similar to a welding rod. The rods of the track are held in relative position to each other with split rings made from the same material. Much of the track was made of 4 rods forming a "tube" for the ball to run inside of instead of 2 or 3 rods which the ball rolls on-top-of. The tracks are braced to each another, like a spider web, which adds to the dense appearance. It uses 8 - 1 inch steel balls.
The construction appears kind of rough as opposed to a finely finished, polished, or painted piece. It also shows some wear from 25 years of service and some repairs are visible. The 2 motors are on a timer so they only run during museum hours. On some RBS it is not uncommon to find fallen balls that have jumped the track -- the Gravitram seems to run perfectly with all balls "in play."
It has two lifting mechanisms, a Archimedean screw and a chain-hook, both of which run the full height. The very long lifting chain also drives a sprocket at the midpoint. This sprocket helps stabilize the chain and drives a large, rotating, 2-arm, ball-moving device, which grabs balls and moves them to a different location.
The Gravitram is full of surprises. It has many clever switches some of which are spring-loaded and quite ingenious. Most of the hardware such as springs, bearings, and worm gears, are custom/scratch built. A favorite feature is the cart. This is a small wagon that carries two balls down a short track. When a second ball drops into the cart, the total weight overcomes a counterweight and the cart rolls downhill. At the end-of-the-line it dumps the balls out and is pulled back up to its starting point by a string connecting the counter weight to the cart.
The Gravitram makes a nearly constant clanking from the balls moving around, there are no gongs or other special sound makers. If you're in the area, the Gravitram is a must-see! The OMSI has many other great exhibits, an IMAX theater and one of the finest scientific gift shops around.
