The angle between the coupler and follower—critical for force transmission. Values near (90^\circ) are ideal; below (40^\circ) or above (140^\circ) cause poor mechanical advantage.
Solving for (\theta_3) and (\theta_4) (the coupler and follower angles) requires solving a , often handled via the Freudenstein equation: 4 bar link calculator
[ r_2 \cos\theta_2 + r_3 \cos\theta_3 = r_1 + r_4 \cos\theta_4 ] [ r_2 \sin\theta_2 + r_3 \sin\theta_3 = r_4 \sin\theta_4 ] The angle between the coupler and follower—critical for
[ K_1 \cos\theta_4 + K_2 \cos\theta_2 + K_3 = \cos(\theta_2 - \theta_4) ] 4 bar link calculator
Given link lengths and crank angle, output the angles of the coupler and follower, plus the coupler point position.
Differentiating the loop equations yields angular velocities using the known input angular velocity.