input (φ) = 120.0°
0°90°180°270°360°
output (θ) = 39.1°
Mechanism classification
Crank-Rocker
AD — ground5.00
AB — crank2.00
BC — coupler3.00
CD — rocker4.00
Ground orientation0°
Coupler Point Study

Place a study point anywhere on or near the coupler.

Along coupler (0 = B, 1 = C)0.50
Normal offset0.00
Geometric Solution

Click each step to see the construction on the canvas. Algebra and transpositions shown at every step.

Known Values
Start with the given measurements
Use these current link lengths and input angle before working through the geometry steps below.
Step 1
Crank Projections
Project the input crank onto x and y to locate point B (also called B′ in construction).
Step 2
Diagonal from D to B′
Use the right triangle from D to point B′ to find the diagonal length h₁ and angle θ₁.
Step 3
Oblique Triangle (Law of Cosines)
Solve ▵D–B′–C using the Law of Cosines to find θ₂.
Step 4
Final Output Angle
Combine the two sub-angles to get the rocker angle θ.