This is a wood and card version of a machine designed by Leonardo da Vinci. We saw a beatiful realisation of the original design, built in wood, at 'The Art of Invention' exhibition in early 2000 and I couldn't resist trying to reproduce it using card and paper on a wooden frame.

When the vertical shaft is rotated continuously the horizontal shaft turns first one way then the other. With the sizes as shown the top shaft turns approx. 240 degrees either way.

For a detailed description of the building method for gears and pinions look at the November Project. This machine uses two 63mm (2.5 in) diameter discs for the contsruction of the main wheel and pairs of 38mm (1.5 in) discs for the two pinions.

The CROWN WHEEL has a half matchstick inserted into each corrugation. Notice that pieces of matchstick are inserted round just less than half the circumference. These 'pegs' must disengage from pinion 1 before engaging pinion 2.This is the fiddly bit! This action is helped by rounding the matchstick ends with fine glasspaper. Loose ones can be glued!

The frame in the illustrated model is built from 10mm square timber. A length of plastic drinking straw, wrapped with masking tape, forms the vertcal bearing.

It's difficult to think up a model that can utilise this mechanism - but it's interesting in it's own right, and well worth making up'.

Although we have built this model with 11 year old children it's better suited to secondary pupils - a history project with a twist!!
Next month's project will be much less demanding - keep watching!