A standard external Geneva drive converts continuous driver rotation into one indexed output step followed by a locked dwell. A driver pin enters successive radial slots, while a concentric locking surface restrains the output wheel between engagements.
Uniform Intermittent Motion Interactive Calculator
Choose three to twelve radial slots, enter a number of complete driver turns and set an inspection position for the schematic. The numerical results are ideal angular calculation for a standard one-pin external Geneva drive—not a speed, acceleration, force or design-rating model.
Equation Used
- The model is a standard external Geneva drive with one driver pin and N equally spaced radial slots.
- Each complete driver turn advances the output by exactly one ideal step of 360/N degrees.
- Radial entry and exit give an engaged driver sweep equal to the supplement of the output step; the remainder is dwell.
- During engagement the animation enforces C/r=1/sin(pi/N) and places the pin center on the active finite radial slot centerline; the locking mark is explicitly schematic.
- Dimensions, clearance, pin and slot width, interference, locking profile, contact stress, impact, backlash, friction, inertia, torque, speed limits, wear, strength and safety are omitted.
Driver Pin, Radial Slots and Dwell Lock
U.S. Patent 2,597,950 describes the conventional Geneva arrangement: a pin carried in a circular path enters successive equally spaced radial slots, indexes the wheel during part of the driver revolution and leaves the wheel stationary for the remainder. A concentric locking surface can restrain the wheel while the pin is disengaged.
During engagement the animation applies C/r=1/sin(pi/N), aligns the pin center with the active finite radial slot and uses the pin-to-wheel-center direction for output orientation. The green dwell-lock mark is schematic because its production profile and clearance are not calculated.
What This Calculator Represents
For a standard one-pin external Geneva drive, N equally spaced slots give an output step of 360/N degrees. Radial pin entry and departure make the engaged driver rotation the supplement of that step; the rest of the driver revolution is dwell.
The entered complete-turn count simply multiplies the ideal step. The inspection-position control changes only the displayed point in a cycle.
Standard External Geneva Angular calculation
engaged driver sweep = 180° - step
driver dwell sweep = 180° + step
ideal dwell share = dwell sweep / 360° × 100%
accumulated ideal travel = complete driver turns × step
Worked Angular Example
With four slots, each complete driver turn advances the output by 90°. Radial entry and exit occupy 90° of driver rotation, leaving a 270° dwell, or 75% of the cycle. Three complete driver turns therefore correspond to 270° of accumulated ideal output travel.
Assumptions and Limits
- Calculated: ideal angular step, accumulated step travel, dwell sweep and dwell share.
- Illustrated: a generic external Geneva driver pin, radial slots and locking surface.
- Not calculated: exact position law, velocity, acceleration, jerk, pin/slot impact, clearance, contact stress, torque, inertia, friction, interference, dimensions, fatigue, wear, manufacturing tolerance, operating limit or safety.
Frequently Asked Questions
Does each complete driver turn produce one step?
Yes, for the modeled one-pin standard arrangement.
Can the index-to-dwell ratio be set independently?
Not in this standard geometry; it follows from slot count.
Why is the minimum three slots?
The two-slot limit is geometrically degenerate for the standard external construction and is excluded here.
Is the animation an exact velocity trace?
No. It is an explanatory engagement sequence.
Does accumulated travel give the output's final wrapped angle?
No. It is an unwrapped sum of ideal steps.
Can this calculator size a Geneva mechanism?
No.
References
- U.S. Patent 2,597,950, Intermittent driving mechanism: conventional Geneva radial slots, circular pin path, stationary remainder and the supplement relation for driver indexing sweep.
- U.S. Patent 2,625,833, Geneva mechanism: single pin, equally spaced radial slots and an arcuate locking rib.
- U.S. Patent 3,443,455, Intermittent motion device: indexed output motion as 360 degrees divided by the number of stops.
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
