This calculator applies the ideal one-pin external-Geneva step and phase relations, then converts the index share to time at constant input speed. It does not cover other intermittent transmissions or real settling time.
Intermittent Transmission Interactive Calculator
Explore ideal external-Geneva step, index/dwell shares and geometric index time at constant driver rpm.
Equation Used
- Standard one-pin external Geneva with N equally spaced radial slots.
- Constant driver speed over one revolution.
- Ideal crank-radius/centre-distance relation a/C=sin(pi/N).
- Index time covers ideal pin engagement only and excludes post-index settling.
- No locking-disk detail, interference, clearance/backlash, acceleration/jerk, payload inertia, torque, contact stress, strength, wear, lubrication, speed limit, accuracy, controls or safety model.
The timing formula applies to a standard one-pin external Geneva. Index time is geometric pin-engagement time, not output settling time or usable process time. Cam indexers, ratchets and other intermittent drives use different relations.
Ideal external-Geneva timing
For N slots, one driver revolution advances the star by 360/N degrees. The pin is engaged over input angle 180−360/N, giving index fraction 1/2−1/N; the remainder is geometric dwell.
The drawing uses a/C=sin(pi/N) and aligns one radial direction with the pin during indexing. Its fixed slot lengths and wheel outline are schematic, and its playback speed does not represent the entered rpm.
Use as a textbook timing check
The outputs can check ideal Geneva phase arithmetic and convert it to time at constant driver rpm. They cannot select a mechanism, determine process throughput or confirm settling and positional accuracy.
Geometric engagement time
Cycle time is 60/rpm seconds. Multiplying by (N−2)/(2N) gives ideal engagement time. Dwell time can be inferred from the complementary share, but real usable dwell is reduced by settling and control margins.
Six-slot example
For N=6 and 60 rpm, star step is 60 degrees, engagement share is 33.33%, dwell share is 66.67%, and ideal geometric engagement time is 333 ms within the one-second driver cycle.
Practical timing and load limits
A working Geneva requires compatible pin, slot and locking geometry. Loads, inertia, clearance and stiffness affect acceleration, settling and positioning accuracy. The geometric engagement time does not determine a permissible speed or the time available for a process after the output settles.
Questions
Does geometric index time include settling?
No. It ends at ideal pin disengagement.
Can this formula be used for cam indexers?
No. Their phase law comes from the cam profile.
Does slot count establish safe rpm?
No. Loads, acceleration, strength, wear and accuracy must be analyzed.
References & Further Reading
- Wikipedia contributors. Geneva drive. Wikipedia
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