I probably don't need one of these and I'm not even sure what I'll use it for, but it sure is cool...
It's a plotter or CNC drawing machine that uses an H-Bot configuration in which both the X and Y steppers are stationary. The original machine is called AxiDraw and is designed & marketed by a company called Evil Mad Scientist. It sells for around $475 and has gone through several design iterations. You can also buy a Chinese version for around $250. Or, you can download the 3D print files from Thingiverse for free. You have to provide the 2 Nema 17 Steppers, 4 of the 8mm hardened steel rods, 8 of the LM8UU linear bearings, 2 GT2 timing pulleys and a length of GT2 timing belt, an Arduino, GRBL shield, and an assortment of screws and hardware. I just happen to have virtually all the other hardware and electronic pieces on hand so my cost is will probably be less than $20 for anything else I need to buy. I did have to buy the small stepper for the Z-Axis. It was about $2.75 with free shipping from aliexpress.
The 3d printer does most of the work and it's just a matter of putting it all together and watching it work. I've already printed most of the plastic parts so I'm about ready to begin assembly. If you're interested, here is a video of the machine being assembled and tested:
