(click to enlarge)
Click!…Whirrr…Hummm…Bang! These are the sounds of “The Flying Marbellos”: a rolling ball sculpture
with marbles and small metal “bugs” to run the show. The purpose of a rolling ball sculpture (RBS) is to
transport balls to the top of a system of tracks, where they proceed to find different and amusing paths on the
way down. Is this a silly thing to do? Yes! Do people love to watch these things for long periods of time? Yes!
Put an RBS in a public place and you can attract a crowd surrounding it. I love watching mechanical things, but
building this turned out to be even more fun.
Since I have a fascination for mechanical things, and also enjoy working with Basic Stamp microcontrollers, this
6 1/2 foot tall RBS finds some different ways of going up with the balls as well as going down. It all starts with a
motor that elevates the marbles to the top, and as they roll down they encounter switches that change paths with
every marble. The insects and spiders add a circus flair to the whole thing. A helicopter carries one marble from
a low platform to a higher one so that it can begin another journey down. An elevator carries another marble to
the top, sends it to drop through the air to a pad where it bounces up and into a basket. One marble lands into
the muzzle of a cannon, where a bug lights a torch, leans over and lights the cannon’s fuse, and then the cannon
fires the marble into the basket. Two marbles at once go down into a tube, where 90 LED lights follow the
marbles, cascading in sequence down the tube. Others follow turns, loops and spirals, jump from a ski jump and
ring bells on their way down.
Once in a while, a marble leaves the track and does not make it back on to the track. When this happens, a marble-rescuing
machine takes the marble back up and puts it back on the track. Some RBS’s are excellent at keeping all balls on the track for
extended periods of time. When marbles bounce, jump or get shot out of a cannon, this doesn’t work as predictably. The marble
rescuer keeps the machine going, despite losing its marbles now and then. It hasn’t stopped me from losing my marbles, though. I
noticed that if no marbles go onto the bottom for a while, observers start getting anxious to see it happen again, so that they can
watch the rescuer put the ball back on the track. Maybe losing your marbles is not such a bad thing.
Gravity makes the marbles come down the tracks, and 3 Basic Stamp microcontrollers help with the 21 switches, four stepper
motors, one servo and 92+ LED’s. I chose Basic Stamps because they are so easy to use. Their online manuals and resources
gave me plenty of information to learn to work with them, without my being an engineer. Coordinating the motors and moving
parts required many changes of the program to get the right “look” and the right smoothness. With the Stamps it was easy to
make changes and evaluate their effects.
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The copter's trolley
One of the big stars of the show (and certainly the biggest challenge) is the helicopter. When a ball rolls into the
cockpit of the helicopter, it flies by means of fishing line leading to a trolley above. One stepper motor, for the
“X” (horizontal) direction of travel, pulls the trolley on a track across the top of the machine. Another stepper
motor raises the copter (the “Y”, or vertical direction), so that when the two motors work together they lead it
on an arc to the upper platform. As the trolley travels from one side to the other, it also rotates the copter, so
that at the top it is facing 90° from where it started.
You might think that since you can control the speed of stepper motors, that you would have complete
flexibility in controlling motion. There are some limitations. The motors’ maximum speed of rotation is limited
because they only work properly up to a maximum speed of the steps, and then the mechanics can’t keep up
with the electronics. With a “PAUSE 1” in between steps in the program, this comes close to the top speed of
the motors I used, which have 200 steps per revolution. To get a fast enough maximum speed of motion, some
mechanical advantage is needed. Using motors with fewer steps per rotation would also increase speed but
sacrifice some smoothness in movement.