Drawing machine

Robotics and electronics discussion Miscellaneous
1

I’ll try to keep this simple. Think of the claw game; the one where you try and grab the stuffed animals. But what I want to do is replace the claw with high powered green laser and the stuffed animals with a piece of wood. So it’s a laser engraver.

I’m really not a hardware guy at all so that’s why I’m posting. I’m not sure if they exist or what to call them, but a server that can keep turning infinitely. Not one that just goes 360 degrees and stops. These will move the rubber bands that will be attached the box holding the laser. The box will slide along 2 metal poles (x,y) axis. But the servos my main problem right now :\

thank you :smiley:

2

You’ve hit on something really neat here, but you’re also opening up a pretty big can of worms. Just to tackle the motor question, you can use either stepper motors, or some sort of non-hobby servo motors (in general, servo just means feedback controlled).

Stepper motors have no actual feedback, but move in known increments in response to a control signal rather than rotating continuously. Most ink jet printers use stepper motors to position the print heads and advance the paper, so you can get very precise linear motion out of them.

You could also use regular DC motors, and turn them into servos with some form of feedback like a rotary optical encoder attached to the motor, or a linear optical or capacitive encoder attached to the moving head.

Now of course you’re going to need something better than rubber bands to move your laser, but you’ve got the right idea. You might search around for examples of homemade CNC (computer numerical control) machines, especially CNC routers, which are usually two degrees of freedom (x and y). CNCzone.com is a good place to start, they have a nice DIY section.

As for the laser, I haven’t played with one yet myself, but I’m not so sure that even one of the new high-power green laser pointers is going to do much of a job of engraving. I’ve seen the videos of them lighting matches and popping balloons, but you can also pop a balloon with a dull carrot (it was on Mr. Wizard!). You might be able to mark wood/paper with it, but not really remove material from the surface. You might look into a lens to focus the laser to a finer, and more powerful point.

Commercial laser cutters and engravers use infrared lasers, which transfer heat much more efficiently than visible lasers. Incidentally, desktop laser engraver/cutters start at around $7,500.

Please post any more questions, let us know how you’re proceeding, and good luck!

-Adam

3

For the laser I’ve been looking at wickedlasers.com, I’ll get one of those and then get a lense cap to make it more accurate/powerful.

As for the software: I’ll input a greyscale image and then the laser will go through pixel by pixel. The darkness of the pixel determines how long the laser will remain over one spot. The size of the pixel will most likely not be the size of the laser beam, so I’ll have the laser move around in a square (and inside the square) to make one pixel, it’s hard to describe what I’m talking about :\

Right now I know java and I’d prefer to program in that right now (I’ll be learning c(++) at UT, so I’m not ready for c just yet). I looked up the stepper motor wiki and have determined that this is what I need. Have any suggestions on where to buy stepper motors? I looked on this site but only found servos and normal DC motors. After I find out what motors I need then I can choose a motor controller.

I didn’t literally mean a rubber band lol. I meant a toothed rubber band like the ones found in scanners (or old ones atleast).

Wow thanks for the cnc link, so much information!

4

Wow, I hadn’t looked at their site in about a year, and I just watched the video of them engraving a floppy disk! Did you see they also sell a set of lens-caps, including one that focuses the laser to a fine point? Depending on how 3D you want your engravings to be though, you might not even need it!

Anyway, stepper motors are pretty cheap, you can get them from Jameco or Digikey, and you can even scrounge good ones form a color printer. The angular step size is built into the motor, so take that into account when you make your selection.

I haven’t yet seen a “hobby” stepper motor controller that I’ve really liked, but you can make your own with a dual H-Bridge and a microcontroller (higher-torque motors can take quite a bit of current, so you’ll want to size the H-bridge chip to your selected motor). Getting a stepper motor just to step is actually not as complicated as it seems at first, but the tricks get more complicated really fast. A Baby Orangutan would be a good choice, if your stepper motor can run on less than an amp.

If you’re interested in spending a little more up front to cut down on your electronics development time (like a couple of hundred dollars), Lin Engineering makes great stepper motors with integrated, daisy-chainable serial controller/drivers (RS-485, you’ll need a serial or USB converter, they sell those too). They let you do neat tricks like microstepping, acceleration control, even storing programs within the controller that execute on startup. I’ve had good experiences with these when I needed to automate something quickly for work, but I haven’t yet sprung for one for personal use. You might even look at just their standalone motor drivers to use with another motor.

Does anyone have a good “hobby” stepper motor controller to reccomend?

-Adam

5

Have you looked at the steppers and drivers from Sparkfun? (That’s a bad site to go cruising on…) Small motors (under an amp per winding), but you wouldn’t need to move much mass with that laser. Each axis would be about $30. I was looking at these for making a very small (1/2" travel each axis) lathe for making scale model parts. (Each time I do a job like that it ties up my tools, which drives me nuts.)

If you’re not too picky about accuracy, I’ve seen people use drawer slides and timing belts (like the ones from Stock Drive Products, not like the ones from NAPA). You wouldn’t get 0.0001" accuracy that way, but you also wouldn’t spend a fortune on your X-Y stage, either.

Lots of info out there for DIY CNC. It’s well worth researching before shelling out money for bits and pieces. One very important consideration is how you intend to drive the thing once you’ve got it built. Lots of options out there for this, too.

Best of luck with this!

Tom

P.S. This may or may not need mentioning, but please Please PLEASE be safe with that laser. I saw they sell a 300mW laser. That’s beyond blindness and on into making that sickening “pop” sound if the beam hits your eye. The folks from Pololu work with lasers and probably have their own set of goosebump stories. I’ve worked around a couple of high powered lasers, and would never treat them lightly. Consider building an enclosure for the thing that is opaque to the wavelengths you’re using, and interlock the door so if the door is opened, the laser goes off.

6

Oh no Tom, it definitely needed mentioning. If you want to see your part as it is being engraved you could use a sheet of red or blue transparent plastic as the lid of your safe-box, but you should test it to see how well it blocks the green laser light before relying on it to save your eyes. It looks like they also bundle protective tinted glasses with their lasers (“LaserShades,” red for green lasers, blue for red lasers), an excellent idea! The lens cap that focuses the laser to a point could also be an added safety feature, since the laser light would disperse past that point.

The last time I was looking for stepper motor drivers I was sort of put off by the one Sparkfun carries (after being spoiled by getting to work with some industrial automation stepper drivers). The price is right, but the current limit is a bit low (sufficient for most motors, I know) and you only have access to one type of stepping. Also, the interface is too simple for my taste, it doesn’t really do enough for you. If I’m going to need a microcontroller to send such basic commands as take a single step in this direction I might as well spend ten more dollars for a Baby Orangutan (which has a slightly beefier dual H-Bridge) and write my own stepping protocol.

The real killer though was the warning: [ul]“Caution: Do not connect or disconnect a motor while the driver is energized. This will cause permanent damage to the A3967 IC.”[/ul] Not just “may cause damage,” but “will cause permanent damage”. This translates in my mind to the more personal message “this thing is very fragile and you will break it Adam.”

Anyway, I didn’t mean to go on a rant, I like most of Sparkfun’s stuff, I just think there is a big hole in the hobby electronics market right now for an inexpensive but full-featured stepper motor driver (hint hint).

-Adam

7

Hahahaha! No, that warning applies for me, too. I didn’t read that far. I did see they were for low-current motors, but they do say they’re intended to drive something you’d pull out of a floppy drive. (Either they said it or I’m making that up after looking at the motor they sell with the kit.) But a good point about the Baby-O costing about the same as their controller. That would be pretty straightforward code to write, you’d get 1A per channel, and you could do all sorts of different drive schemes.

I’ve noticed most of the hobby-level stepper drivers carry that same warning: Unplugging while in use lets out the magic smoke. I guess in a way I’ve more or less made peace with that, but it’s certainly not something we’d put up with at work. (Practically everything we get in the door at work gets the “yank every cable, fiddle with every switch” test to make sure it can recover gracefully.)

Ok, I’ll jump:

I would be interested in seeing a motor driver board for a 200 oz-in or slightly larger stepper motor that could survive plugging and unplugging when under power and in motion, and doesn’t cost as much as a Gecko.

There are many many MANY DIY CNC projects that would benefit from such a beastie. One that’s still on the back-burner in my shop after too many years is a hexapod milling machine.

Back to the lasers, I liked the idea of getting laser safety glasses, matched to the laser. But all you need is for someone to open the door to the room at the wrong time, and you’re up a creek. One laser I worked on was an IR CO2 laser that was used on an optical bench with an unexpanded beam. We covered what we could, but the big fear was that someone would drop something shiny like a wrench, and have it fall through the beam. The specular reflections from that would’ve been literally blinding. If I remember right it was a 40W laser.

It’s an old joke, but the second rule of laser safety is, “Don’t look into beam with remaining eye.” I leave it to the humor impaired to figure out what the first rule of laser safety is. :wink:

Tom