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Four-Bar Linkage

The Grashof condition (shortest + longest ≤ the other two) decides whether any link can fully rotate. The transmission angle tells you how well force passes to the output — keep it above about 40° or the linkage binds.

Ground link r1

Input crank r2

Coupler r3

Output rocker r4

Crank angle θ2 (°)

Grashof

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Type

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Output angle θ4

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Coupler angle θ3

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Transmission angle

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“No closure” means the linkage cannot physically assemble at that crank angle — a non-Grashof linkage only works over a limited range.

A helper, not a substitute for engineering judgment. Verify against the governing standard.