David Mandala shows the Gocupi that at Linaro Connect. The cool thing (beyond that is was made by a couple of guys from the DallasMakerSpace) is that it is a real project that uses an ARM embedded computer and it could do more if it had a more powerful ARM embedded computer.
It is also a contraption more commonly referred to as a ‘drawbot’ or ‘polargraph’. The gocupi is a robot that suspends a pen or marker between two stepper motors and draws on a vertical surface. Each stepper motor has a spool attached to it’s shaft which is wound with a thin braided line, and these spools move simultaneously to control the position of the pen that hangs between them.
The positioning is all accomplished by using a polar coordinate for each point on a path for each stepper motor. To determine how the pen should move from one point to the next the gocupi calculates the velocity and acceleration based on a number of factors, the most notably being the position on the drawing surface. The gocupi knows lines near the edge of the page drawn at high speed have a tendency to produce an unintended line or may cause the pen to bounce off of the surface creating dots and dashes instead of a line. This is all taken into consideration for each transition of the pen from on point on a path to the next. To further put that process into perspective, it is not uncommon for a drawing to consists of 800,000 points (or more) and take 45 minutes to an hour for the gocupi to draw.
Find out more about it at: http://gocupi.com/