The vast majority of automated machine tools, including CNC mills and 3D printers, utilize a conventional Cartesian layout. That means each of the three dimensions in physical space is actuated independently. A Prusa i3 3D printer, for example, has one stepper motor for the X axis, one for the Y axis, and two steppers acting in unison for the Z axis. But other kinds of layouts are possible. The most common of those is probably the “Delta” style of robot often seen in 3D printing. If you’re working on a vertical surface, it’s possible to use a pair of steppers to triangulate an end effector. This 3D-printed whiteboard robot works in that way.
This whiteboard robot is comprised of three distinct subassemblies: the hanging end effector carriage, a stepper motor at the top left of the whiteboard, and another stepper motor at the top right. The carriage hangs between the two stepper motors on a GT2 belt. By turning the stepper motors you adjust the length of the belt between the carriage and the top corners of the white board, which lets you move the carriage to any point on the whiteboard. In practice, that only works well in the central area of the whiteboard, because a lot of tension is required to pull the carriage to the very top of the board. Reaching the sides of the board would result in too much slack on one side.
The creator of this project, Tyler Gerritsen, doesn’t provide much information on what kind of software and hardware are being used for control. But we do know how it’s working mechanically. Two pancake style NEMA 17 stepper motors are positioned at the top corners of the white board on 3D-printed mounts. The carriage is also 3D-printed and contains three retractable dry erase markers and an eraser. Only one motor is needed to switch between those, thanks to a clever spherical Geneva drive. That’s essentially a standard Geneva mechanism with the input shaft turned to be perpendicular to the output shaft. The result is a robot you can build yourself that can draw and write on a whiteboard in up to three different colors.