This design of oscillator is taken more or less from the Bob
Thomas drawing. It consists of two triangular plates, a top
plate and a bottom plate. The bottom plate has a cup in each
of its three corners facing up. In each cup sits a marble.
The top plate also has a cup in each of its corners but these
are on the underside of the plate and face down. Each cup of
the top plate sits on one of the bottom plate's marbles.
This arrangement allows the top plate to move freely over the
bottom plate, as long as the marbles remain in the cups.
Note that cups are bowl shaped causing up and down movement
of the top plate as it moves horizontally.
The top plate has a piece of aluminum on its top surface, this
aluminum having a notch in it. The bottom cone sits in this notch.
This allows the bottom tip of the cone to move horizontally and
vertically.
One more detail is that in the center of each plate is a
magnet. The magnet for the bottom plate sits on top of the
plate. The magnet for the top plates hangs under the plate.
These magnets are oriented so that they attract each other but
are spaced out due to the height of the marbles such that
they do not touch. These magnets pull the cone tip back to the
center.
Looking down at the surfaces of the plates that face each other.
On the left is the bottom plate with the marbles sitting in its
three cups. In the center is the magnet. On the right is the top
plate. Note that it is upside down as the three cups are normally
sitting on the bottom plate's marbles.
Closeup of the bottom plate. The cups are the bottoms
of pop cans turned upside down. The magnet is attached with duct tape
that runs through slots in the wood.
Top view closeup of the bottom plate. The magnet is
attached with duct tape. It is not taped to the plate. Instead it is
taped to a piece of wood that is screwed to the other side of the plate.
The next picture shows this piece of wood.
Its height is adjustable by adding cardboard disks between it and the
piece of wood that it is taped to.
Top view showing the two plates as they
would appear when sitting at the bottom of the drum. Note the piece
of wood that is screwed to the top of the top plate. The notch that
the bottom cone sits in is in a piece of aluminum that is taped to
the piece of wood.
Side view showing the top plate sitting on
the marbles which are in turn sitting on the bottom plate.
