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 pool ball.
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 pool balls.
This arrangement allows the top plate to move freely over the
bottom plate, as long as the pool balls 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 pool balls 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 pool balls 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 pool balls.
On the left is the bottom plate, turned upside
down so as to show its under surface. On the right is the top surface
of the top plate. The dark mess in its center is a bunch of duct
that holds the piece of wood that holds the aluminum that has the
notch in it. The three pool balls are sitting on the table
in between the two plates.
Almost side view of the bottom plate with
the pool balls sitting in the three cups. The magnet is visible
in the center. The cups were made of Christmas tree balls that
normally hang on Christmas trees. These were bought in a craft
store. They come as two plastic half spheres which people can
join together after filling them with various decorative things.
I simply used a hack saw to cut them to the needed size.
Close-up of a pool ball sitting in its cup.
Note that it is not a snug fit, allowing the pool ball to
move around in the cup.
The cup without the pool ball so that you can see
that it is bowl shaped.
Side view showing the top plate sitting on
the pool balls which are in turn sitting on the bottom plate.
A gap can just be made out between the two magnets.
Top/Side view showing the two plates as they
would appear when sitting at the bottom of the drum.
Other details
Currently I have 4.5 inch magnets attached to the oscillator and
the gap between them is very small. The strength of these magnets
are such that they hold the oscillator too rigidly centered. It
is designed such that I can experiment with different sized
gaps between the magnets.
