Finally got the code running to draw some images...

Ran into a couple hurdles. The laser was positioned almost perfectly, then something unexpected happened... The disk warped due to the heat. And, in the process, the laser was no longer in focus, believe it or not, even though the disk is sandwitched in its case and could only warp a tiny bit... it wouldn't burn.

So I came up with an idea... Why not just move the focus of the laser back and forth? The end-result is simply that it sits at each point for a few seconds while adjusting focus between its maxima. Was pretty easy to do, the same H-Bridge chips I'm using for the steppers seem to work fine for the lens's "voice-coil." PWM, (one resistor), and done.

The images don't quite look right, however... The columns seem staggered, as though the vertical motor isn't positioning to the same point each time. I'm not sure what the reasoning for this is... maybe it has to do with my microstepping technique. There's certainly plenty of "slop" in the *rotational* axis, but that shouldn't affect the vertical (unless the rotational axis reverses direction, take a look at the "engagement" mechanism on a floppy next time you see one, they're not exactly precise).

I tried a couple different techniques. The first was obviously too hopeful, drawing in a zig-zag raster-fashion... One column down, the next up, etc. Then I tried "homing" between each column... The vertical motor/carriage reacts differently depending on which extreme is "hit". At the lower extreme, the sled's attachment to the worm-gear slips, apparently intentionally. Fine, but there's really no way for the system to know when it will reengage; it may happen in a half a turn, or a quarter-turn, etc. At the upper extreme, however, the motor itself is actually stalled, and misses steps. This seemed to me like a great place to "home", since the motor would always be at the same position (right?). Well, that may be contributing to these staggered columns, as I had run some other experiments that suggest it doesn't actually arrive at the same position each time, even after homing. (Maybe if I did *not* use microstepping during homing... hmmm...)

And, as far as the rotational motor, I tried to measure the "engagement slip" to allow for back-and-forth motion, but it was flakey. And, later, I noticed that the disk actually shifts vertically depending on which direction it's rotating (again, take a look at the floppy engagement thing, it makes sense; it's slanted). Woot!

And then there's the rubber-wheel I'm using, which might lend to some more imprecision, as well as requiring a certain amount of force on the motor's shaft... And... That amount of force is *right at* the limit for how much the stepper can drive without missing steps. Weird.

Anyways, here's the results:

This was a much-too-hopeful first-drawing attempt of the cat... If you look close, you might see one, but if you look at the actual image, you might be surprised. (You can also see the warping of the disk).

This was a test to see how much of the badness of the last image was due to image-skew... I treated it as though the vertical and horizontal were perpendicular rather'n radial... this would be a rectangle...

And, there (and here), you can see the weird jaggedness in vertical offsets...

Below is supposed to be a smiley-face, not a Pacman ghost!