The original steam engines used pistons that were powered in only one direction. As the piston pulled down, it pulled on a chain link over a curved rocker similar to the nodding donkeys seen in oil fields. When James Watt realised that he could dramatically increase the power and efficiency of the engine by powering the piston in both directions he set out to find a simple way of using the straight line motion of the piston to drive the circular motion of a drive shaft.
The Watt Linkage, shown here, is the solution he came up with. This mechanism is still widely used. The straight line motion is at the centre whole in the blue bar. It is not absolutely straight though in a mechanical situation it is probably straighter than the tolerances of the bearings. The figure of eight dotted line shows how the centre point moves over its full range of movement, not just the straight area.

I think we need a downloadable, make-able version of this nifty mech!

No iFrame ‘;
print ‘
Using HTML 5 ‘;

print ‘
Using Flash’;

Hopefully this animation will work in all sorts of browser windows from Windows machines, Linux boxes to iPhones and iPads. Let me know how it’s looking for you.

Make your own Watt Linkage here.