The plan was to make an automaton who would draw... as a beta version this one does make 'marks', but it's not really drawing as intended.

These are little 'arms'. They are going to follow grooves in a drum.

The drum is made from an old empty tube of silicone sealant. The ends are capped with core board, mounted around the centre on a pencil and washers added to the ends.

Automaton Arms

This is the key mechanism. The little arms underneath are exposed above as two pivoting levers. The main X arm swings backward and forth matching the motion of the little arm underneath. It has a hoop at the end to allow the Y actuator to fit through. The main Y arm acts at right angles to the little arm underneath. With a hinge joint it is able to move the actuator up and down through the hoop at the end of the main X arm.

Recording our drawing

Now we have to record a correct motion of the little arms underneath which will result in a drawing. I have drawn a little duck, and marked 24 spots on his outline. The next step is to wrap paper around the drum. Now mark 24 intervals on the drum. Finally as you rotate the drum to each of the 24 positions, mark where the little arms line up (given you move the actuator over the matching spot on the duck drawing). Then join the dots with a line as shown below.

Once we have a set of lines, glue this onto some suitable plastic, and cut out along the lines. Then glue the plasic onto the drum ensuring you seperate the sections enough to leave a groove for the little arms to follow.

Skipping a beat

To ensure the little arms didn't jump out of the grooves on the drum, I added little bits of plastic to the corners to 'reinforce' them.

OK... it's kind of a fuzzy duck, but it's a start.

The two main issues with this automaton are the lack of rigidity in the drawing arm, and the fact the pencil was a bit wobbly in it's holder. The ideal solution would be to machine proper rigid parts for the top half, then the motion of the little arms underneath would be reproduced with much more accuracy.