This revision restores the documented three-circle selector: a slotted pinion shifts along its shaft to engage one of three concentric pin circles and obtain one of three speed changes.
Structural checks before adding an actuator
The actuator mounting points in pin-wheel and slotted pinion mechanism should be treated as structural load points. Pin size, clevis width, bracket stiffness, and alignment can matter as much as the actuator force rating.
When comparing a cylinder to an electric actuator, convert the discussion into stroke, force, speed, duty cycle, and installed length. Matching one specification is not enough.
Pin joints should be reviewed under load, not just assembled by eye. Small bracket offsets can create bending moments that are not obvious until the actuator is near full load or the mechanism reaches one end of travel.
- Keep side load out of the actuator rod by guiding the moving member separately.
- Verify pin diameter, clevis width, bracket stiffness, and alignment under load.
- Check that deflection will not change the actuator load path during operation.
For FIRGELLI actuator projects, compare product families through the FIRGELLI actuator families and use the linear actuator replacement finder when replacing an actuator from another manufacturer. The selection should stay tied to real stroke, force, and mounting dimensions.
Three-Circle Pin-Wheel Speed Selector
Select the 12-, 18- or 24-pin circle, declare the slotted-pinion slot count and input speed, and compare the three ideal indexing ratios. Counts are transparent educational geometry, not a design specification.
Equation Used
- Three declared concentric pin circles contain 12, 18 and 24 equally spaced pins.
- The selected circle alone engages the slotted pinion.
- One passing pin advances one pinion slot in the ideal indexing model.
- The slotted pinion rotates opposite the pin wheel.
- Pin and slot profiles, clearance, contact ratio, load, friction, wear, manufacturing tolerances and shifting dynamics are excluded.
Restores the documented three-circle speed selector and removes unsupported performance, tolerance and application claims.
Three pin circles provide three selectable speed changes
Movement 208 in 507 Mechanical Movements describes three circles of equally spaced pins on the face of a pin wheel. Shifting the slotted pinion along its shaft brings it into contact with one circle or another, producing three changes of speed.
Hiscox later describes the same pin wheel and slotted pinion and again identifies shifting the pinion along its shaft as the means of changing speed.
A historical selectable rotary transmission
The source establishes continuous rotary transmission and three selectable speed changes. It does not provide a named machine, load rating, speed limit, material, clearance or service schedule, so this revision does not invent them.
An ideal declared indexing ratio
If the selected circle has N equally spaced pins and the pinion has S equally spaced slots, one pin-wheel revolution presents N pins and advances the pinion through N slots. The ideal output/input speed magnitude is therefore N/S; external engagement reverses direction.
This count identity does not establish workable pin shape, slot shape, center distance, contact stress or efficiency.
Compare the three declared pin circles
With a six-slot pinion and a 30 rpm pin wheel, the declared 12-, 18- and 24-pin circles give ideal output speeds of 60, 90 and 120 rpm respectively, in the opposite direction.
What the historical source does and does not establish
The three selectable pin circles and sliding pinion are documented. The former page's flour-mill case study, impact limits, debris tolerance, exact clearances, wear diagnostics, fatigue life and manufacturing tolerances were unsupported and are removed.
A practical design requires a complete tooth or slot profile, interference check, strength analysis, materials, lubrication and a safe shifting arrangement.
Pin-wheel selector questions
Is this a Geneva intermittent drive?
No. The cited mechanism provides continuous rotary motion with three selectable speed changes.
How is the speed changed?
The slotted pinion is shifted along its shaft to contact a different pin circle.
Are 12, 18 and 24 historical dimensions?
No. They are declared educational counts used to make the three choices explicit.
Pin wheel and slotted pinion references
- 507 Mechanical Movements, movement 208: three equal-spacing pin circles and a shaft-shifted slotted pinion provide three speed changes.
- G. D. Hiscox, Mechanical Movements, movement 926: speed change by shifting the pinion along its shaft.
- Internet Archive scan, Hiscox movement 926: searchable scan record of the illustrated mechanism.
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