I made a spray painting gondola, see step 11 for information. This ends up being a nice upgrade since you can only write with a marker on certain walls, but you can spray paint on any wall (brick, cement, etc.) ;). I've also added a video below
When I thought about what making something on a computer real one of the first things that came to my mind was Facebook wall posts. Wouldn't it be cool if I could post them on a real wall. Well now I can!
This robot draws posts to your virtual wall in Facebook, onto a physical wall. To do this I looked at various drawbots that used two steppers and a pen to create large drawings. You could easily do this with an Arduino, but I wanted to see what I could do with the EiBotBoard that came with my Eggbot. I also harvested the motors off the Eggbot to make this happen. Since I don't have a 3d printer yet (hint hint . . .) I made this with parts that don't need to be printed, but it could be improved on with a few 3d printer parts.
You could draw directly on the wall. Since I'm married I'm not allowed to do that though so I have mine draw on a white board mounted to the wall ;). The frame is portable so you can easily move it somewhere else, plug it in and go. It supports multiple fonts (stolen from the Eggbot Hershey Text plugin for Inkscape)
Since this drawbot basically just draws text, it doesn't have to be from Facebook, any text you want it to render would work as well.
Step 1: Drawbot Basics
The length of the string is "c". "a" is the distance from the motor down vertically to where you want to be (the Y coordinate). "b" is the distance from the motor to where you want to be (the X coordinate). Doing this calculation for both of the motors gets you the distance you want each of the two string to be to land on a certain point. You want your frame to be much bigger than the area you're drawing on, because certain places are difficult to reach if it's not. In the picture attached to this step you'll notice there are two triangles, one with A1, B1, C1 and the second with A2, B2, C2. So:
A1² + B1² = C1²
A2² + B2² = C2²
And solving for C (the length of the string) we do:
C = square root of (A² + B²)
A decent write up on this can be found here http://www.marginallyclever.com/2012/02/drawbot-overvie/