Geneva indexer: plan view (2D)

A Geneva drive converts continuous rotation into intermittent indexing. A pin on the drive crank enters a radial slot of the cross, turns it by one step (90 degrees for four slots) and leaves, while the cross stays locked during the rest of the revolution. With tangential entry the follower speed starts and ends at zero, so there is no impact. For n slots the velocity ratio is (lambda cos f - lambda^2) / (1 + lambda^2 - 2 lambda cos f) with lambda = sin(pi/n).

What this 2D view adds

• A plan view with the crank, pin path and slot centre-lines.
• Follower angle, velocity ratio and acceleration ratio against drive angle with a live marker; the acceleration step at engagement is the reason fast indexers use cams instead.

Honest simplifications

Ideal rigid parts: no clearance, friction, backlash or locking-arc wear. Shares its kinematics module with the 3D page.