Presets
Playback
Parameters
Layers
Readouts
Model check
The science
What you see
The mechanism from above. The driver (left) turns at constant speed and carries one pin; the Geneva wheel (right) has four radial slots. The pin enters a slot, turns the wheel by 90 degrees and leaves; then the driver's lock disc keeps the wheel still.
Geometry
Centre distance a = 2.43 model units and pin radius r = a / sqrt(2), so the pin enters tangentially to the slot. The pin is engaged for 90 degrees of every input turn (a quarter), and the wheel rests for the other 270 degrees.
Speed ratio
At the middle of the indexing the pin moves perpendicular to the line of centres, so omega_out / omega_in = r / (a - r) = 1 + sqrt(2) = 2.414. The ratio is zero at the entry and exit edges, so there is no shock at the start and end of the index.
Check
The curves use the exact pin-and-slot solution from the 3D page's mechanism module (copied unchanged), so both versions show identical angles. The checks compare the numerical derivative with the formula, confirm 90 degrees per turn and that the pin always lies on a slot axis.
Simplifications
Rigid parts, no backlash, friction or inertia; the real accelerations of a heavy wheel would need torque limits.