mr-rob:
I thought about doing something similar back at my old job when we did an autopsy on a laser barcode scanner. Then my coworker told me he trashed the mirror-servo assembly.
Sorry to hear you where turned off from the project because of your coworkers carelessness. However, I think my projector demonstrates very well that you certainly don't need specialized parts if you are crafty. In fact, my mirror array is extremely crudely built, and it still works great for my purposes. I used a computer fan, a VHS tape reel, a large bottle cap, and 6 square mirrors that I bought at a local arts and crafts store (25 mirrors for $2). All of those parts are held together with hot glue.
I have been meaning to share my story of how I constructed the mirror assemble since my first post.
Here it goes, for those that are interested...
How I constructed my mirror assembly:
I started with a brushless computer fan. Not all fans are the same; I made the mistake of buying a new one with a 3rd wire for speed monitoring. I eventually discovered that it had very poor low speed torque and was unable to accelerate my mirrors to any descent speed. Additionally, its speed monitoring wire was also useless to me because it pulsed a signal twice during a single rotation, leavening me guessing at the phase of rotation. I ended up using a fan from and 10+ years old computer power supply.
Then I used a reel from a VHS tape. I snapped off the transparent side leaving me with a shape of a disc on top of a cylinder. I applied hot glue to the bottom of the cylinder and attached it to the top of the fan. While the glue was still hot, I spun the disc with my fingers and made tiny adjustments to its position until it was nearly perfectly centered on the motor. I than took a bottle cap ( 4.5 cm wide, 2 cm tall), and hot glued it upside down to the top of the VHS reel. Again, I made adjustments to center it while the glue was still hot.
I am not sure if this next step was necessary, or even helpful. I wanted to add mass to the outer edges of the disc, so I hot glued 9 pennies on the underside along the edge. In theory, adding this mass would help in two ways. First, it would minimize the any oscillations that might occur at high rotation speeds. And second, the increased rotational inertia would help to maintain a more constant rotation speed. To ensure balanced placement, I aligned the pennies along 9 raised ridges that where present in the shape of the reel.
Before attaching the mirrors, I glued the motor down on top of the project case. I also mounted the laser into position and aimed it to where the mirrors would be. I took a sheet of paper, drew 6 lines, each about 5 cm apart, and taped it to a wall about 10 feet away. With the laser on, I applied hot glue along the bottom edge of a mirror and placed it onto the top of the reel. I then applied glue to the back of the mirror and the rim on the bottle cap. At this point the mirror was now redirecting the laser to a point on the wall above the paper. I pulled the top of the mirror away from the rim of the bottle cap until I lowered the beam to the top line on the paper. I made sure to apply enough hot glue to form a bridge across the gap between the back of the mirror and the bottle cap. I held the mirror in position until the hot glue hardened. I repeated this for the next 5 mirrors, aiming each at the corresponding drawn line and using the ridges in the reel as a guide to ensure good spacing. I made sure to number the mirrors with pencil so as to keep track of which mirror was supposed to be aimed at which line.
With all 6 mirrors attached, the platform was now balanced enough to spin at low speeds. I powered the motor intermittently to maintain a slow speed and watched as 6 horizontal lines were projected onto the wall. It was now apparent that the mirrors where not as well aligned with the lines drawn on the paper as I wanted. Some were too high, and others too low. To make adjustments, I used a micro torch to reheat the glue bridge for a misaligned mirror. Only a second of heat was enough to make the glue soft again. If the mirror was one that was too low, I would apply some force to the front of the mirror to squeeze the glue and angle it more upwards. While the glue was still slightly malleable, I powered up the motor. Again 6 lines where projected, but because the glue of one mirror was soft and slightly elastic, its height would vary with rotation speed. I then carefully controlled the speed of the motor, with a push button, to pull the misaligned mirror into alignment. Once aligned, I maintained speed for as long as necessary as for the glue to re-harden. The result, one perfectly aligned mirror. I repeated for a couple others that were not well aligned.
At this point, all mirrors were attached and aligned, but at high speeds, balancing issues caused a very noticeable vibration. I made a key observation at this point. At low speeds the projected lines were in alignment, but at higher speeds, some lines would shift up, while other shifted down. This was due to tilting of the platform caused by the balance issue. I realized that the shifting lines where telling me exactly how the center of mass was misaligned. A downward shifting line corresponded to a mirror which was tilting downward which corresponded to too much mass on that side of the platform. To correct the balance issue, I simply added a small amount of mass to the opposite side. After some repetitions of making adjustments and retesting, I managed to produce a well balanced platform capable of over 1500 RPM without noticeable vibration.
So there it is. Why did I share all this? I would like to see others make attempts at this type of project. As I predicted before even starting, building the mirrors assembly was one of the most, if not the most, challenging stages of the project. My first attempt was a success, but only after many hours of frustration and a lot of luck. My second attempt (described above) went much more smoothly, most due to using improved techniques. Several people, both here and on YouTube, have expressed interest in building their own. My hope is that if they choose to attempt it, and they read my story, they will save themselves a lot of time and frustration. Even if they are on the fence about attempting it, maybe my story with encourage them to give it a try.