Hiscox’s double-pawl ratchet wheel uses two curved pawls on a moving lever. One drives the wheel during one handle stroke and the other drives it during the return stroke. The wheel therefore advances in the same direction on both strokes. This is a different arrangement from a single drive pawl plus a fixed holding pawl.
Double-pawl Ratchet Wheel Interactive Calculator
Rock the handle through two driving strokes. Compare tooth count, angular advance and average wheel speed while the curved pawls alternately engage the same ratchet wheel.
Equation Used
- One tooth advanced on each handle stroke.
- Two strokes per complete handle cycle.
- Rigid pawls and ideal tooth contact; no load rating.
Normalized one-tooth-per-stroke demonstration. Tooth-count changes rebuild lever geometry. No strength, safety-rating or spring-dynamics calculation.
Two strokes, the same wheel direction
The blue and gold pawls share the moving pin of a lever, whose frame pivot is at the right. As the handle rocks, one pawl remains against a tooth’s radial driving face while the other rides over the tooth ramps. Their roles reverse at the end of the stroke.
The animation uses a normalized one-tooth-per-stroke geometry with the pawl plates mounted in front of the wheel and projecting toes reaching back to its teeth. This axial offset keeps the curved plates clear of the wheel body. Pawl lengths remain fixed, the handle pin follows a circle about its frame pivot, and the active pawl closes its pin-to-tooth linkage. The returning pawl follows the actual displayed tooth boundary. Ideal spring seating is assumed at a tooth drop.
Changing tooth count rebuilds the illustrative lever sweep and pawl seating geometry to retain one tooth per stroke. It does not represent swapping a wheel into an otherwise unchanged manufactured assembly.
Compare tooth count and operating rate
Use the tooth-count slider to compare the angular advance of each handle stroke. Use the complete-cycle rate to compare average wheel speed. One complete cycle means an outward handle stroke and its return.
This is a kinematic explanation of the two-driving-pawl arrangement. It does not size teeth, springs, pins or bearings and does not establish a hoist or restraint load rating.
One tooth on each half-cycle
For N teeth, tooth pitch and advance per modeled handle stroke are 360/N degrees. Two such strokes form a complete handle cycle, so cycle advance is 720/N degrees. At n complete cycles per minute, mean wheel speed is 2n/N rpm. Entered cycle period is 60/n seconds.
Both pawls drive: each handle stroke advances one tooth, and the return stroke adds another tooth of rotation in the same direction.
Example: 12 teeth and 12 handle cycles per minute
Each half-stroke advances the wheel by 30°. A complete handle cycle advances it by 60°, so six cycles produce one wheel revolution. At 12 complete cycles per minute, average wheel speed is 2 rpm.
The instantaneous speed varies through each stroke and falls to zero at handle reversal. The animation does not claim perfectly uniform output speed.
Illustrative geometry, not a rated ratchet
The wheel has asymmetric radial driving faces and sloping return faces. One pawl at a time carries the ideal drive reaction. Two pawls do not automatically double tooth strength or provide a specified safety rating.
Clearance, spring dynamics, impact, tooth rounding, friction and wear are omitted. The return pawl is shown seating ideally when it passes a tooth edge. Playback timing is adjusted for inspection and labeled separately from the entered cycle period.
Double-pawl ratchet questions
Is one pawl just a holding pawl?
Not in this illustrated mechanism. Both pawls take turns driving the wheel.
Does adding a second pawl halve the tooth pitch?
No. In this model each half-stroke advances one full tooth. A half-pitch staggered detent is a different arrangement.
Why does the lever sweep change with tooth count?
The normalized geometry is rebuilt to keep both pawls correctly seated at reversal and retain one tooth per stroke.
Can I use the calculator for a load rating?
No. The outputs are angular travel, mean speed and cycle timing only.
Historical construction reference
Gardner D. Hiscox, Mechanical Movements, Powers and Devices, printed page 254, figure 1001 (PDF page 264), shows the two curved pawls and lever driving on alternate strokes. The animation uses an explicitly normalized construction to demonstrate that operation.
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