Thu, 30 Sep 2010
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!
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Comments (7)

  • Anonymous May 16, 2011 at 9:19 am

    Hey Rob, how do you do the

    Hey Rob, how do you do the hammering man?

  • Anonymous October 31, 2011 at 2:13 am

    I would be interested in

    I would be interested in knowing that too.

  • Anonymous January 5, 2012 at 9:42 am



  • Anonymous November 26, 2012 at 4:19 pm

    My name Daniel joe kimberley

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

  • John H January 4, 2013 at 5:31 pm

    Hello Rob,
    I’m looking for a

    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 February 6, 2014 at 6:47 pm

    Perf for my homework thanks
    Perf for my homework thanks xxxxxxxxxxxx

  • Anonymous May 4, 2016 at 11:30 pm

    hey rob just wondering how

    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

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