Moving Cloud Projector for Portables and Small Planetaria

By John T. Meader Northern Stars Planetarium, Fairfield, Maine
As it appeared in "The Constellation", Vol. 29, No. 4


Cloud Projector Diagram


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.


  • Electric Drill & Bits
  • Soldering Iron & solder
  • Screw driver
  • Pliers (with wire cutter)
  • A Saw of some kind if you are going to cut your own plywood

Materials List:

  • Flat black paint
  • 1- .25 rpm synchronous motor (surplus)
  • 1- 8 inch diameter piece of 1/8" Plexiglas
    (the glass store will cut it for you)
  • 1- 8.25" diameter piece of 1/4" plywood
  • 1- Piece of black felt
  • 2- screw base bulb sockets (Radio Shack part #272-356)
  • 2- GE #13 screw base flashlight bulbs (Radio Shack will provide equivalent)
  • 1- AA Battery holder for four batteries (Radio Shack part #270-391)
  • 1- 25 ohm Potentiometer (Radio Shack part #271-265B)
  • 2- Project Boxes (Radio Shack part #270-233)
  • 1- 6 foot AC Cord (Radio Shack part #278-1255)
  • 2 - nuts and bolts
  • 4- wire nuts (2 large, 2 small)


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:


Wiring Diagram


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
Fairfield, ME 04937
(207) 453-7668

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