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Linkages are an essential part of many mechanisms. They can be used to change direction, alter speed and change the timing of moving parts.
In the hammering man example two linked linkages are used to convert the small linear movement of the drive shaft (bottom left) into first a rotational body movement and secondly a fast hammer movement. Compare the speed of the hammer with the speed of the drive shaft!
The basic 4 bar linkage. All four bars make up a parallelogram. Two, equal length orange shafts and the distance between the joints on the red moving bar and yellow fixed bar being equal. The movement of the top arrange shaft exactly shadows the movement of the lower orange bar.
By changing these lengths and the lengths of the other bars different movements can be achieved.
Different Lengths. This time, two different lengths of bar, the two long bars, yellow and red are the same length as before.
Look at the tip of the red shaft, notice how it moves smoothly until the last second then flips to the right. The same effect is used in the Motley Man in my book Paper Automata to make him look up at the last moment of his bow.
Quite an extreme arrangement this! With the two long bars crossing over each other. A more extreme 'kick' in the orange bar this time at the end of the green bar's travel. Looks like a likely mechanism for a model!


Anonymous (not verified)

Hey Rob, how do you do the hammering man?

Anonymous (not verified)

I would be interested in knowing that too.

Anonymous (not verified)


Anonymous (not verified)

My name Daniel joe kimberley and I am 10 and this site is super cool!!!!

John H (not verified)

Hello Rob,

I'm looking for a mechanism for rocking the legs in my frog and crab clocks.   I'm sure that a Scotch Yoke setup would work, similar to what you used in Nessie, but I'm wondering if there's an alternative solution.


John Hutchinson

Hi John, Looks like a fun project! I think I would probably use a rotating disk and a couple of pushrods rather than the scotch yoke. The bearings are easier. - RI

Anonymous (not verified)

Perf for my homework thanks xxxxxxxxxxxx

Anonymous (not verified)

hey rob just wondering how you attach the mechanism to the hand crank cheers Jake

You would attach the linkage at the bottom left of the image to a crank.- RI