Scott Russell linkage

A Scott Russell linkage gives a theoretically linear motion by using a linkage form with three portions of the links all equal, and a rolling or sliding connection. It can be used to form a right-angle change of motion, linear-to-linear.
The linkage is named for John Scott Russell (1808–1882), although watchmaker William Freemantle had already patented it in 1803.
A different form of the linkage has been used in a front-wheel-drive vehicle with solid rear axle to control lateral movement, and with a flexing elastomeric connection instead of the rolling or sliding connection.
The linkage does not share the disadvantages of the asymmetric Panhard rod and although more compact than Watt's linkage has all the forces in one link.