By John T. Meader Northern Stars
Planetarium, Fairfield, Maine Tools: Materials List: PLEASE NOTE: Refer to the diagram at
the top of the page as you read the following
descriptions. Paint one side of the Plexiglas flat
black. Let dry. Scrape off a few streaks of paint in a
circular motion around the Plexiglas, these will be the
clouds. Don't take off too much paint, you can always do
more later if you want more clouds. Paint the 8.25 inch plywood disk flat
black also. Let dry. Screw one of the project boxes to the
center of the plywood disk. This will be the motor box.
Drill a hole big enough for the shaft of the synchronous
motor to pass through the box cover so that the hole is
in the center of the plywood disk. Mount the motor using
the two small bolts to the inside of the box cover. Drill
a hole in the side of the motor-box for the power cord.
If the cord is attached to the synchronous motor using
wire nuts, be sure the wire nuts or connectors are inside
the motor box. Run the power cord across the face of the
plywood plate and off the side. Staple it in place to
secure the cord. Give yourself enough cord so that you
can easily reach an outlet or extension cord. Screw the second project box to one
edge of the 8.25" dia. plywood disk. This will be the
control box. Drill a hole in the outside side of this box
the correct size for mounting the potentiometer. Glue or
screw the battery holder to the inside of the motor-box.
Drill a hole through the wall of this box big enough to
pass the two small wires going to the bulb
sockets. Mount the two bulb sockets to the
plywood base on the other side of the disk from the
control box. Separate them by 3 to 5 inches. The
projector can be made with one bulb, but the cloud
motions becomes more dynamic with two bulbs. Wire them in
series to each other and the potentiometer. The
potentiometer has three terminals, use the center and the
right terminals to connect the wiring to. The connections
should be soldered at the bulb sockets and the
potentiometer; the wires can then be connected to the
battery holder using the two small wire nuts. The wiring
for the bulbs should look something like this: You might also want to purchase a knob
(Radio Shack part #274-403) for the potentiometer to make
turning it easier and to dress up the finished
product. Attaching the Plexiglas disk to the
base can be accomplished in several ways. The best way is
to use a shaft-coupler, which is a small metal sleeve
that fits over the motor's post and is held in place
using a set-screw on the side of the sleeve. The sleeve
will extend above the end of the motor post and there
will be a second set-screw for attaching another rod. We
cut a nail so that it was the correct size to pass
through a small hole in the center of the Plexiglas disk
and then fit snugly into the shaft-coupler. This method
works well; however, shaft couplers, though very simple
devices, are seldom carried by many hardware stores.
A simpler, but less effective, method
is to drill the hole in the Plexiglas slightly smaller
than the motor post, then carefully push the Plexiglas
onto the post allowing the friction to hold it in place.
It is best to use a slightly thicker piece of Plexiglas
(perhaps quarter-inch) to give more friction. This works
all right if you are very careful with the disk, but if
you are going to carry the projector around a lot, like
portable users might, it probably won't hold up as well
as the shaft-coupler. The black felt is then glued in a
strip around the edge of the plywood base so that it
stands up past the edge of the Plexiglas disk. This works
as a light baffle to stop light leaks from around the
edges of your new projector. At this point your new cloud projector
should be ready to go! Enjoy!
Northern Stars Planetarium
and Educational Services
As it appeared in "The Constellation", Vol. 29, No.
4
During the April 1995 MAPS
meeting at Raritan Valley Community College, a
mini-conference took place aimed at portable planetarium
users from New Jersey, Pennsylvania, New York, and a few
other far-flung places. I was asked to present a series
of presentations about ways to develop peripherals for
portables. While many of the special effects that I use
range from slide projectors to video, the effects that
often impressed the attendees the most were the
simplest--shadow projectors. Shadow projectors made a
strong impression on the attendees because they saw them
as very effective and very simple. Simple enough so that
they might be able to build such devices themselves--with
perhaps a little instruction. Here I would like to
present a few simple instructions for building a moving
cloud projector. This is presented with the new MAPS
members from the Portable Mini-Conference in mind.
(the glass store will cut it for you)
Fairfield, ME 04937
(207) 453-7668
info@northern-stars.com