We have also been playing with chalk feeding for scribbling with sidewalk chalk like Nikos' Artist Robot.
Here is the latest - lots more info and development can be found on the forums at this thread.
First is the latest AutoCAD drawing of the Basic Info and Concept of the Chalk Feeder Tube. This is version 2.2.
Here is the second test video - shot in my carport. Sorry about the vertical shoot. I was excited about showing of the the clever Propeller Beanie - I guess.
And finally here is a still photo... Lots of fun...