Step 1: How it works
Like I already pointed out, in each motor there is a circular mirror. These mirrors are from disposable dental mirrors, because they are already rounded, have a nice size and are easy to work with. The mirrors are glued in a coaxial way with the motor, but they have a small tilt. When the laser strikes the spinning surface of the tilt mirror, it is reflected forming a circle. If this circle is projected into another spinning tilt mirror it will form a variety of shapes, depending on the motors velocity and other factors. Adding a third motor just opens the possibility to even more complex shapes.
If you want to see it in a more scientific way, the resulting shape is the plot on polar coordinates of the following equation: f(r,ø) = A sen (x* ø) + B sen (y* ø) + C sen (z* ø). Were “A”, “B” and “C” are the amplitude that is the mean of how much the mirror is tilt, and “x”, “y” and “z” are the velocity of each motor and the offset between them.
So to be able to change the shape that is plotted you need to change the amplitude, the offset or the velocity. I can’t think of a simple way to change the amplitude, you couldn’t control the offset unless you used stepped motors and that is out of my reach. So what I did was to change the velocity of each motor.