January 7th, 2011 by bdring
This little product from egg-bot.com has been showing up all over the web lately. It is primarily designed for coloring eggs and other small sphere-ish items. For the simplicity of it, it does a fantastic job and produces some amazing results.
With the recent discussion thread on the buildlog.net DIY laser forum about making an open source rotarty attachment for lasers, this has a whole new appeal. There are even some discussions on the eggBot FAQ about using this for lasers.
On the Egg-bot website, they down play the suitability of it and mention safety issues. To be fair, it is not really too suitable to laser use because of the size limits (1.25-4.25″ Dia and 6.25 max. long) and the special interface. The cost of $195 is also a little high, but that is due to the included controller and pen motors, etc. But lets get past all that and assume we have one and we want to hack it for lasers.
The first thing that comes to mind is dumbing it down to a simple rotary attachment to run inside the laser. This would be rather simple. Lets say you want to engrave a 1 inch square logo on a little 1.5″ diameter anodized flashlight. First you would strip it down to just the basic mechanism and the rotary stepper motor. The controller and pen controls are not used. You would then plug the stepper motor directly into your Y axis stepper driver. Be sure to dail down the current to what the Egg-bot stepper can handle. You now need to create your logo image. The image will be 1 inch tall, but the width needs to be stretched/squashed to fit the work piece. Since linear surface motion is dependant on the diameter of the item, a little calculation needs to be done.
Say you have a 200step/rev stepper, a 10 microstep driver and a 1000dpi laser controller. Your new resolution will be (Motor Res * Driver Res) / (Dia * PI). In this case (200 * 10) / (1.5 * 3.14159) = 424.4 dpi. Your laser thinks 1000 steps will go an inch, but in reality it is going to go (1000/424.4 = 2.36) inches. The solution is to make squash the image narrower by that amount, so your image is 1000 pixels high by 424.4 wide. That is it. 424.4 dpi is probably a decent enough resolution for a logo, but that is going to drop quickly with as the diameter gets bigger. If your stepper driver can increase the resolution, that will help.
image credit: http://dnashopper.com
The second hack the comes to mind is letting the EggBot control things. It has a controller capable of running two small steppers. Hook the laser’s X axis up to the EggBot controller and let it do the work. That might work, but it would require some serious hacking to get the laser enable to work right. The pen control is probably the candidate to do this. You might even be able to just hook up a push button that clicks when the pen is in the drawing position. I think a really low power level on the laser would be needed.
The third hack might ditch the whole rotarty thing and keep just
the controller. Actually you can buy the controller on it’s own from
Evil Mad Science (out of stock for a while). I’ll bet you could hack the open source software to make it become the complete laser controller. It has two built in stepper drivers, a USB connection, a voltage regulator and a whole lot of other useful things. I am sure you could get it to be a cutter controller and you might be able to get it to do some simple engraving. The data transfer of the image data might be tricky with limited memory, but it is probably doable. It has hobby servo drivers which might be a good source for PWM power control.
I would love to get one for the pure hacking fun of the project, but I don’t have the time right now. If someone has a laser, has the hacking cred to tackle a project like this, I might consider a donation to the project.
About the resolution issue of image design…
The DSP controller from LightObject lets you specify the distance the laser head actually moves for each step from the controller as a means of calibrating controller space with real-world space. You can set this independently for x and y axes. So rather than design on a squashed scale, design at normal and tell the controller to squash or expand it as needed. Basically, you just lie about what the real world movement is. You could do all the calculations for various diameters or write a simple calculator. Then, just plug in the appropriate numbers at “print” time.