BB8 plotter

I played around with the idea of the sphero rig of Shacksandbeans, thing:1266810
and gave BB8 a good time with it.
Wheel diameter 5 to 6 cm, any wheel you like will do. The pen should be able to move freely in the vertical direction. The pen holder can be adapted to the pen diameter. The pressure on the paper is just caused by its own weight.