An external Geneva drive converts continuous rotation into indexed steps separated by a dwell. Explore how slot count determines the output step and the portions of driver rotation spent moving and dwelling.
External Geneva Index and Dwell Calculator
Enter slot count and constant driver speed. The worksheet reports the standard external-Geneva index angle, ideal driver engagement/dwell angles and one-revolution period; it does not predict stress, impact, backlash or service speed.
Equation Used
- One driver pin indexes a wheel with N equally spaced radial slots.
- Pin entry and exit are radial and the conventional center-distance/crank-radius relation is used.
- The locking sector holds the wheel ideally outside pin engagement.
- Clearance, pin radius, impact, elasticity, inertia, load, lubrication and wear are excluded.
The driver pin advances the slotted wheel one station at a time. Slot count sets the ideal index, engagement and dwell angles; driver speed sets the revolution period.
Driver pin, radial slots and locking sector
An external Geneva drive converts continuous driver rotation into intermittent output rotation. The crank pin enters one radial slot, indexes the wheel by one station and leaves radially; while disengaged, a mating locking sector restrains the wheel.
The animation uses the standard center distance and crank-radius relation for the selected slot count. It is an ideal kinematic map, not a tolerance or force model.
Index and dwell timing
Use the calculator to find the ideal angular split of one driver revolution. Detailed design requires chosen center distance, pin and slot dimensions, clearances, materials, inertia, load and target life.
Standard external-Geneva angles
The move and dwell driver angles sum to 360 degrees. At constant driver rpm n, one input revolution takes 60/n seconds.
Four-slot example
For N=4, each index is 90 degrees. The driver pin is engaged through 90 degrees and the wheel dwells through the remaining 270 degrees. At 60 rpm, one driver revolution takes 1.000 s.
Ideal timing is not a speed rating
Patent literature describes the pin entering and leaving radial slots and the locking element holding the wheel between indexes. It also documents acceleration, shock and wear limitations. Slot count alone does not establish a safe operating speed; loads, dimensions, materials and the motion profile also matter.
Geneva-drive questions
Does N set the output step?
Yes, for this one-pin external form the ideal step is 360/N.
Is dwell the output-wheel angle?
No. It is the portion of driver rotation during which the wheel is locked.
Does the entered rpm rate the mechanism?
No. It only converts one revolution to time.
Patent and mechanism references
- US2597950A, Intermittent driving mechanism: radial-slot indexing, locking cam and the engagement angle as supplement of index angle.
- US2625833A, Geneva mechanism: radial pin entry/exit and intermittent locking topology.
- US6183087B1, Geneva mechanism and motion picture projector: slot count, index duration and acceleration/load limitations.
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