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Engineering Kit

Four bar linkage calculator

A free online four bar linkage calculator and simulator. Enter the four link lengths and the mechanism animates through its full cycle, tracing the coupler curve, so you can see whether the crank rotates fully before you commit to the geometry.

Try the live demo
Four bar linkage schematic with the ground link, crank, coupler and rocker labelled, and the coupler curve traced as a dashed loop.

Try it in your browser

Drive the inputs and watch the geometry redraw in real time. The preview deliberately stops short of the numbers: transmission angle, coupler curves and crank-rocker geometry all stay in the Android app.

Four bar linkage demo

Change the four link lengths and watch the mechanism cycle and trace its coupler curve.

200 mm
60 mm
200 mm
160 mm

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What the four bar linkage calculator works out

Four Bar Linkage is deliberately narrow: it solves one sizing problem completely, with the assumptions written down next to the result.

Crank-rocker check
whether the shortest link can fully rotate as a crank.
Transmission angle
through the cycle, including the worst-case value that governs force transmission.
Coupler curve
traced by any point on the coupler, for path-following mechanisms.
Dead-centre positions
the crank angles where the rocker reverses, and the resulting rocker swing.
Link feasibility
whether the four lengths can assemble at all.

Typical jobs

100% offline

Four Bar Linkage for Android

The Android app reports the crank-rocker check, the transmission angle range, the rocker swing and the coupler coordinates through the cycle, and animates the mechanism offline. No account, no sign-in, no data connection.

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