DIY laser spirograph (intro)

Simple laser show everyone can build.

DIY laser spirograph.  Cool and affordable laser show.

According to Wikipedia, spirograph is a geometric drawing toy that produces mathematical curves known as hypotrochoids  and epitrochoids.
Yes, it sounds like quite complicated scientific apparatus and, believe me, mathematical equations describing those curves look terrifying too, but it's a wonderful toy so if we leave boring science behind we'll learn that it's quite easy to build one and it's a real fun to play with.

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Well, since this device is named as "Laser spirograph", it's obviously that it employs laser to draw distant images. For home laser show any low power laser will do work; something like this green laser module from Deal Extreme.

Now let's recall few important safety rules we all must follow.
When experimenting with 10 mW and more powerful lasers always use proper laser safety goggles.
Never point laser in direction of people or animals.
When conducting show or public demonstration always project laser on non-reflective surface to avoid accidental exposure to scattered beam.
And never leave laser equipment unattended when curious kids are nearby.

Laser beam moves way we want by means of spinning mirror. Basically it's a mirror attached to the shaft of DC motor but (that's important) mirror should be mounted with tilt. Mirror's tilt results in changing of angle of reflection of laser beam when mirror spins; therefore, laser draws a circle.
Now if we add smoke to the scene (Did you turn your soldering iron OFF?) we'll get simple laser effect so-called "Time tunnel".

To get real effect of spirograph we should add one more spinning mirror. Mirrors should be aligned in such a way that laser beam reflected by first mirror stays within area of second mirror. Now by changing speed of motors we can produce huge variety of cool patterns.
There's no limitation in enhancing visual effects, as long as we maintain optical alignment; we can add more spinning mirrors,  speaker mounted mirror, beam splitter/chopper, etc.

DIY laser spirograph  -->>>  (part 1)