The blue crank rotates continuously while its pin slides inside the red rocker's slot. The rocker swings about fixed pivot O₂. Crank radius and pivot spacing change the angular swing; arm length changes the travel of its tip.
At 1×, 15 rpm takes 4 seconds per cycle. Playback scale changes elapsed time only, not the motion relationship. Drawing scale stays fixed during playback.
Change blue values → use the button to return to the drawing
1 mm ≤ a < d ≤ 10,000 mm; d+a+1 mm ≤ L ≤ 10,000 mm; speed: 0.1–3,000 rpm.The pin completes the blue circle while red point B travels back and forth along an arc. The arm slows near each limit, then reverses.
O₁ and O₂ are fixed. Crank pin A slides along a straight slot through O₂. A = (a cos φ, a sin φ), O₂ = (d, 0). Rocker angle above the leftward horizontal is δ = atan2(a sin φ, d − a cos φ). Total swing is 2 asin(a/d), and B = O₂ + L(A − O₂)/|A − O₂|. The model requires a < d for full input rotation and L ≥ d + a + 1 mm to keep the pin within the arm length. Slot and rod widths are illustrative. Friction, clearance, forces, strength and collisions are not calculated.
