I've finally got my message printed. The kit I'm using is the mDrawbot. You get the parts and instructions for four different drawing machines. The one I was playing with yesterday was a drawing turtle. Today I've switched to a robot drawing arm, which works a lot more reliably. There is also an "eggbot" for drawing on eggs and a dangling string based one that lets you draw huge pictures on an easel.
The kit is part of the MakeBlock family which are based on sturdy aluminium parts which you bolt together. It reminds me of Meccano of old, but with much stronger elements that you could use as the basis of proper devices. You can even get a laser attachment for the plotter that you can use in place of a pen to perform laser engraving and cut thin paper.