Mechanical & Aerospace
Four-Bar Linkage Lab
The four-bar is the building block of mechanisms — wiper arms, oil pumps, suspension. Drag the ground, crank, coupler and rocker lengths and the mechanism animates, solved by loop closure at every crank angle. Grashof's law (shortest + longest ≤ the other two) decides whether the crank can rotate a full 360° (a crank-rocker) or only rock back and forth, and the dashed line is the coupler curve traced by a point on the floating link.
Crank-rocker
Mechanism
Full 360°
Crank rotates?
Yes
Grashof S+L≤P+Q
Grashof's law (S + L ≤ P + Q) decides whether the crank can spin all the way round. Make the crank the shortest link and you get a crank-rocker — the basis of windscreen wipers and oil pumps; the dashed trail is the coupler curve.
How to use this simulation
The four-bar is the building block of mechanisms — wiper arms, oil pumps, suspension. Drag the ground, crank, coupler and rocker lengths and the mechanism animates, solved by loop closure at every crank angle. Grashof's law (shortest + longest ≤ the other two) decides whether the crank can rotate a full 360° (a crank-rocker) or only rock back and forth, and the dashed line is the coupler curve traced by a point on the floating link.
Everything runs in your browser — no sign-up, no download. Change a value and the result updates instantly, so you can build a feel for how each input shapes the outcome. It pairs with Crameleon's practice exams and step sheets when you want to go from intuition to working the problems.