Marble
Adding
Machine
MAKE A MECHANICAL, GRAVITY-POWERED, BINARY CALCULATOR
THAT USES WOODEN LEVERS
AND CHANNELS TO COUNT.
BY MATTHIAS WANDEL
Computers add binary numbers constantly, but we never see how. This elegant machine does the math using glass marbles.
I started building marble track machines years
ago using Lego. I experimented with all sorts of
crazy ways for the marbles to descend. One was a
rocker that shunted a stream of dropping marbles
one-by-one to alternating sides. If you cascade
three of these toggles down to the left, every marble
flips the rightmost toggle, every second marble flips
the middle toggle, and every fourth flips the leftmost. Interpret each toggle’s state as left = 0 and
right = 1, and you have a binary counter. Add more
toggles, and it can count more.
I realized I could turn the counter into an adder
by dropping marbles onto toggles other than the
rightmost. I added a marble hold-and-release shelf up
top to act as an input buffer, another underneath as an
output buffer, and a clear-register mechanism to reset
all toggles. I moved from Lego to wood, and refined
the design a few times. Here’s the latest edition.
Photograph by Garry McLeod
80 Make: Volume 20
