Linkage Mechanisms: The 4-Bar and Beyond
Linkages convert one motion into another using only rigid links and joints — the quiet workhorses of mechanical design.
Linkages convert one motion into another — rotary to linear, continuous to oscillating — using only rigid links and joints. They are the quiet workhorses of mechanical design.
The 4-bar linkage
The 4-bar linkage (crank, coupler, rocker, ground) is the foundation. By changing link lengths you can generate an enormous range of output motions without a single gear.
- Crank-rocker for oscillating output
- Double-crank for full rotation
- Parallel-crank for exact coupling (like locomotive wheels)
Knowing when a linkage can replace a cam — and when it cannot — is what separates an elegant design from an over-engineered one.
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