"Marble Coaster" is a Rolling Ball Sculpture. It is great fun to see one in a public place, because they
attract quite a crowd at times. Some people will remain for extended periods to try to see everything
that is happening. This one was in the waiting room of my dental office, and attracted more than just
my patients to come see it. (It got replaced at the office by "The Flying Marbellos", "H-2-Opus", and
"Wizard's Run".) It did some time at the Solano County Fair (Best of Show) and the California State
Fair (First Award of Excellence, and Creativity Trophy).
The marbles are elevated at the back left by a pair of sawtooth-shaped ramps, that boost the marbles
up one step at a time. Then 3 mechanical switches channel the marbles onto 4 different tracks.
Tracks are made of 1/8 inch steel welding rod, and most of the connections are brazed. The 7 rpm
motor delivers a marble every 8+ seconds to the top. A pulley and counterbalance system on the
lifting mechanism makes for an easier load on the motor.
Another element is a vertical tube, with pieces of 1/4" copper tubing protruding all around it on pivot axles
made of 1/16" brass rod. As the marble travels down the tube, it hits the copper tubes and makes them tilt
upwards in a spiral pattern, making noise and visual action as the marble falls through it all. It is seen on the
upper right of the top picture.
Here the marble loads into the top of a pendulum, the arm of the pendulum angles back until the counterweight
slows it to a stop. Then it accelerates back up until at the top the marble is dumped onto another track to
continue its journey down. The marbles need to be within a narrow range of weight for this to have the right
effect. The counterbalance weight can be adjusted for different weight marbles. It needs to be set for the
heaviest marble, so that it will return to the top. For the heaviest marble the pendulum travels way out to almost
horizontal, takes its time doing so, and looks cool. If there are marbles present that are much lighter, the
pendulum only goes a little ways, does it quickly, and doesn't look as good. Between the bounce and the
pendulum, I could only use about one out of eight marbles. At 25 cents a marble, I think it is worth it for these
click to enlarge
One of the most popular features is the "bounce". A marble circles around at the upper left, drops onto a purple pad (toward
the bottom on the left), and bounces into the air and then lands in a basket (circle near the bottom of the sawtooth elevator).
The purple pad is a slice of a superball on a steel disk, the disk can be aimed by three setscrews underneath, which can direct
the path of the ball after it bounces. See the details on the construction page.
This is a great effect, but it relies on the sphericity of the marble for an accurate bounce. Glass marbles are not all accurately
spherical, so less than half of available marbles bounce reliably enough to serve the purpose.
In addition to the elements mentioned above, other elements include a spiral, chimes, spinning
rods, a loop, and a bell. The bell is actually a hole saw cutter, which is made of a steel alloy that
rings very well. The chimes were from wind chimes.
It is quite a challenge at times to bank the tracks so that the marbles don't fly off the track. I
occasionally had to resort to a 3rd rail to insure that the marble stays on on some fast curves.
A view from above