Stepper motors

Drawing pen

Adjustable high-current stepper controllers

Pulleys

Drawing board

« At far left is MAKE publisher Dale Dougherty and his drawbot portrait; here’s Melvin with his.

24V and 5V power supply

MAKE controller

MAKE Controller could put out, so I ordered some Interinar microstepping motor controllers that could be adjusted to output the power the steppers needed.

Holding the paper down turned out to be somewhat tricky — we needed a separate base and springs to hold it stable. We added legs to the contraption, and John Blunt, our woodworking neighbor, made a beautiful oak base with clipboard clips to keep the drawing paper secure.

The drawbot process starts with a photo taken by my MacBook Pro’s iSight camera. Any image would work, but using the iSight removes the inconvenient step of importing photos to the computer. Then you save the image as a .bmp file, and drop the file into our Launch Drawbot program. Launch Drawbot converts the color image into a simple black-and-white bitmap using Peter Selinger’s mkbitmap utility, and then converts the resulting bitmap into a vector graphic representation using Selinger’s Potrace. Mkbitmap and Potrace are both open source, available on sourceforge.net.

Launch Drawbot shows you a preview of the drawing before you start, so you can get an idea of how it will work. You can also adjust the size of the dark areas, where the contrast edges are drawn,

and how thick the fill lines are. The better the image going in, the better the drawing coming out will be, and we discovered that filtering the image before generating the vectors is critical to reducing the line count, which reduces drawing time. We didn’t want to wait 8 hours for our pictures.

Once the actual drawing starts, the program sends packets of data over Ethernet to tell the drawbot which coordinates to go to. As soon as you command the drawbot to begin, it puts the pen down on the paper and starts drawing. It draws an outline of all the areas first, and then goes back and fills in the shading.

Everybody who worked on the drawbot agreed that no matter how much you suffer from OCD, it’s spellbinding to watch and can maintain your attention for hours on end. Feel free to download the code for the project, play with it, and make it better. It’s under the GPL license, which means you’re free to use it as long as you release your changes under the same.

For more, go to makezine.com/11/drawbot.

Bre Pettis produces Weekend Projects and other MAKE Video Podcasts on the MAKE blog at makezine.com/blog.

Make: 37