An internal Geneva drive turns continuous input rotation into intermittent output steps. Its pin engages a radial slot for more than half a driver revolution, giving a longer motion interval and a shorter dwell than the corresponding external form. Use slot count and completed driver turns to calculate index angle, accumulated travel and the driver-angle intervals for motion and dwell.
Internal Geneva Drive Interactive Calculator
Calculate ideal index travel and driver motion/dwell intervals for a single-pin internal Geneva from slot count and completed driver turns.
Equation Used
- One drive pin and one output index per driver revolution.
- Conventional ideal internal Geneva timing with radial slots.
- Constant driver speed only for interpreting angle fractions as time fractions.
- The animation follows ideal pin-centre geometry; the outputs do not give velocity, acceleration, loads or component dimensions.
The results give ideal timing and index travel. The drawing follows a pin-centre constraint but does not specify pin diameter, slot width or locking surfaces. It does not calculate velocity, acceleration, contact loads or strength.
Internal Geneva timing and finite centerline geometry
A single driver pin engages one radial slot during each input revolution and advances the output by one slot pitch, 360/N degrees. Unlike an external Geneva, the internal form's driven interval is longer than 180 degrees of driver rotation.
The animation uses ideal centerline geometry with crank radius a=C sin(pi/N). During engagement, the pin center lies exactly on and within the finite active radial-slot segment. The slot and wheel envelope scale from the full engaged pin-center excursion. Pin diameter, slot width and locking surfaces are not designed.
Timing exploration
The calculator compares ideal slot-count timing before detailed mechanism design. A buildable drive requires exact center distance, crank radius, pin and slot geometry, locking surfaces, clearances, materials, lubrication and dynamic load analysis.
Motion and dwell intervals
Index angle is 360/N. For a conventional internal Geneva, the driver motion interval is 180+360/N degrees and dwell is 180-360/N degrees. These add to one 360-degree driver revolution. For example, four slots give 270° motion and 90° dwell, while six slots give 240° motion and 120° dwell.
Six-slot example
With N=6, each driver turn advances the output 60 degrees. The ideal driver motion interval is 240 degrees and dwell is 120 degrees. After five completed driver turns, ideal accumulated output travel is 300 degrees.
From geometry to a working drive
Slot count fixes ideal index and timing intervals, but not safe speed, shock, torque or accuracy. The animated output angle follows the ideal pin-center/radial-slot constraint through engagement, and the pin center remains inside the finite slot and wheel envelope. It does not generate pin diameter, slot width, clearance, material ligaments or locking-surface geometry and contains no dynamic analysis.
Frequently asked questions
Why is motion longer than dwell?
For N slots, the conventional internal form has a driver motion interval of 180°+360°/N. It therefore exceeds 180°, leaving less than half a revolution for dwell.
Does Completed driver turns change the animation speed?
No. It multiplies the index angle to give accumulated output travel. The animation demonstrates one repeating input cycle, not all entered turns.
Does the diagram provide construction dimensions?
No. It illustrates pin-centre and radial-slot geometry. Pin diameter, slot width, clearances, bearings and locking surfaces need a separate design.
Can the angle intervals be used as time fractions?
Yes, if input speed is constant: divide each interval by 360°. With six slots, motion takes two-thirds and dwell one-third of each cycle.
Can this set an allowable operating speed?
No. Inertia, contact loads, clearance, stress and lubrication are not calculated.
Technical references
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