Theo Jansen's kinetic sculpture Strandbeest. A wind-driven walking machine.

An eight-bar linkage is a one degree-of-freedom mechanism that is constructed from eight links and 10 joints.[1] These linkages are rare compared to four-bar and six-bar linkages, but two well-known examples are the Peaucellier linkage and the linkage designed by Theo Jansen for his walking machines.

bars of identical colour are of equal length

There are sixteen different topologies of eight-bar linkages which are distinguished by their non-isomorphic linkage graphs. Of these 16 topologies, nine are in class (4, 4, 0, 0), five are in (5, 2, 1, 0) and two in (6, 0, 2, 0).

The Peaucellier linkage (or Peaucellier–Lipkin cell, or Peaucellier–Lipkin Inversor) is an eight-bar linkage constructed from hinged joints that traces a pure straight line from a rotary input. It is named after Charles-Nicolas Peaucellier (1832–1913), a French army officer, and Yom Tov Lipman Lipkin (1846–1876), a Lithuanian Jew and son of the famed Rabbi Israel Salanter.[3][4]

This linkage clearly consists of eight bars when the ground frame is counted as a bar. The Chebychev–Grübler–Kutzbach criterion shows that an eight-bar linkage must have ten single degree-of-freedom joints, while the Peaucellier linkage appears to have only six hinged joints. This is resolved by noting that four of the hinged joints each connect three bars. This is considered to be a special case of two joints that are located in the same place. Thus, six plus four provides the 10 one degree-of-freedom joints.

The Peaucellier linkage is a (4, 4, 0, 0) eight-bar linkage, which means four of the bars have two joints and four bars have three joints.

Animation of one leg of Theo Jansen's Strandbeest