I use plastic mirror, drill part way into the back by hand, sit the motor shaft into the hole and put a drop of cyno-acrilate on it. I can (almost) guarantee that you will not get it straight........ which is a good thing as the slight wobble will give you the effect you are after.
I used the tray-motor from a CDrom (the disc motor is a useless stepper motor in new models). Shift the wheel up or down so that it does not stick out. Be careful that the mirror is precisely centered. (turn the wheel using a rubber band to check, if the mirror is rectangular then all the corners should trace the same circumference)
This is supposed to be two intersecting tunnels, but it got smeared by the 1.4 seconds shutter time.a
