![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Watts_Linkage.gif/640px-Watts_Linkage.gif&w=640&q=50)
Watt's linkage
Four-bar straight-line mechanism / From Wikipedia, the free encyclopedia
A Watt's linkage is a type of mechanical linkage invented by James Watt in which the central moving point of the linkage is constrained to travel a nearly straight path. Watt's described the linkage in his patent specification of 1784 for the Watt steam engine.
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Watts_Linkage.gif/640px-Watts_Linkage.gif)
Dimensions (unit lengths a, b):
Link 3: a + a
Links 2 & 4: b
Vertical distance between ground joints ≈ 2aHorizontal distance between ground joints ≈ 2b
Thus, link 1 (total distance between ground joints):
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/0/0a/The_Kinematics_of_Machinery_Fig_1.png/640px-The_Kinematics_of_Machinery_Fig_1.png)
Today it is used in automobile suspensions, where it is key to a suspension's kinematics, i.e., its motion properties, constraining the vehicle axle's movement to nearly vertical travel while also limiting horizontal motion.