Geneva Drive

Four slots, one pin — continuous rotation in, a stepping index out, with a locked dwell between indexes.

Geneva drive animation A driver crank turns continuously. Its pin engages one of four radial slots in the driven wheel and advances it one quarter turn; for the rest of the cycle the driver's circular locking boss nests in a concave arc of the wheel and holds it still. Four indexes per driver revolution. O1 O2 driver pin driver crank turns continuously radial slots (four, in the wheel) dwell restraint locking boss nests in the wheel's concave arc Geneva drive — four-slot Maltese cross O1, O2 fixed axles — moving: crank, pin, wheel
phase: indexing

The driver turns continuously, but the wheel moves only in steps. Over 90 degrees of driver rotation, the pin engages one radial slot and pushes the wheel exactly one quarter-turn — the indexing phase. For the remaining 270 degrees, the pin is outside the slots and the driver's circular locking boss nests into the wheel's concave arcs, holding it still — the dwell. The cycle then repeats with the next slot, giving four indexes per driver revolution.

Source: Geneva drive — Wikipedia. https://en.wikipedia.org/wiki/Geneva_drive