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Very Basic Laser Show

    The most basic. low cost laser show you can build is based on 'spyrograph' patterns generated by rotating mirrors mounted on DC motors. The information is provided here for fun and experimentation as this effect is rarely used in professional laser shows.

PARTS:

A HeNe or diode laser (you can use a laser pointer)
Two small DC motors and hardware to mount them
Two variable voltage DC power supplies for the motors (model train power supplies work well)
Two small lightweight front surface mirrors (preferably circular)
Some 5 minute epoxy glue

    You will need at least two DC motors that can rotate at speeds between 300 and 3,000 RPM and two independent DC power supplies. Model train transformers work well for this application as the more modern ones use pulse width modulation to control the speed of the trains. Switches that allows the motors to go in forward or reverse also add to be effects generated.
    Obtain two thin, round Front surface mirrors at least 25mm [1"] in diameter. Mount these on the ends of the motor shafts [epoxy works well]. When you mount then. you don't want then exactly square and true to the shafts, you want then slightly tilted so that a laser reflected from the spinning mirror will draw a small circle. If you have access to a lathe, you can fashion a mount that allows you to adjust the 'tilt' of the mirror and the size of the circle that it will draw.
    Once the mirrors are mounted and the glue has dried, place the motors on brackets so that the mirrors face each other with a short distance [25mm - 1" or less] between them. The motor/mirror assemblies should also be set up in such a way that the angle between them can be adjusted. Send the laser beam into the first mirror and start it rotating. Now adjust the angle of the first motor/mirror assembly so that the circle it is projecting falls onto the mirror of the second assembly. When this step is complete, start the second mirror spinning and adjust the angle of the second assembly so that the pattern is projected without hitting any part of the first mirror/motor assembly [see diagram].

Laser Spirograph

    By varying the speed of the mirror, you are controlling the frequency of the circle that it draws; by changing the direction you get added effects. The effect on your wall or screen is produced by spinning a circle in a circle. The 'beats' between the frequencies of the two circles control the complexity of the patterns produced.
   You can increase the complexity and range of the effects by adding a third and even a forth motor/mirror assemble with variable DC power supply. If you do add an additional assembly, you have to be sure that it deflects the bean into a very small circle so that you do not 'overfill' the last mirror in the array.
    To add yet another simple variation to your basic laser show, you can add chopping. Make a small disk that has slots or teeth around the perimeter [a miniature circular saw blade works]; you can also use a miniature DC fan. Mount this securely on a separate motor with a separate variable DC supply. You might want to choose a motor that can go quite fast for this application. If you place this in the beam before it hits the first spinning mirror, the spinning slotted or toothed disk will cause the laser to 'pulse' on and off. This causes the spyrograph to appear as a series of dashed lines. With the right combination of speeds, traveling black segments will move through the spyrograph patterns adding to the effects.
    The number of slots or teeth around the perimeter of the disk will determine how many times per revolution the laser is 'pulsed' - more teeth/slots gives more pulses. If you use a disk with triangular teeth like a circular saw, putting just the tips of the teeth into the beam will produce very short off pulses. Moving the disk so that the laser is closer to the bottoms of the teeth will produce longer off pulses adding to the effects you can produce.

 

Most of the information and ideas in the Hobby Archives have been contributed by hobbyists and experimenters. If you have any comments or ideas to share, please contact us by E-mail.

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