Historical treadle mechanisms connect a rocking footboard to a flywheel crank through a pitman rod. This calculator reports selected crank stroke, entered pitman length, their ratio and the simple in-line closure margin L-r. It does not predict treadle travel, spring return, flywheel speed, power or machine performance.
Spring-Return Treadle to Pulley · Selected Crank Ledger
Explore selected crank stroke, pitman length, length ratio and ideal in-line closure margin.
Equation Used
- r is the selected crank-pin radius.
- L is the selected centre-to-centre pitman length.
- The 2r result is crank-pin diametral stroke, not footboard travel.
- The closure margin L-r refers only to an ideal in-line crank-slider condition.
- Treadle pivot geometry, offsets, spring, flywheel, belt, cadence, forces and losses are excluded.
Former recommended minimum-pitman and side-angle-risk claims are removed; the candidate reports entered length and an exact in-line closure margin.
Selected crank-and-pitman ledger
A crank pin at radius r has a diametral stroke of 2r. The entered pitman length L is compared directly with r: an ideal in-line crank-slider can close through a full revolution only when L is at least r. The dimensionless length ratio is L/r.
What the calculator determines
Use it to compare selected crank radius and pitman length values. Actual treadle motion requires the treadle pivot, attachment point, offsets, spring, flywheel, belt and machine load.
Exact selected relationships
Selected crank stroke S=2r; selected rod ratio lambda=L/r; ideal in-line closure margin=L-r.
Selected-input example
At r=28 mm and L=112 mm, the selected crank stroke is 56 mm, the ratio is 4.00 and the ideal in-line closure margin is 84 mm. These values do not establish footboard travel or machine speed.
Not a treadle-performance model
The ledger omits treadle lever ratio and arc, joint offsets, spring stiffness and preload, flywheel inertia, belt ratio and slip, operator cadence, torque, losses and downstream machine load.
Questions
Is 2r the treadle travel?
No. It is only the crank pin's diametral stroke; footboard travel depends on the rest of the linkage.
Is L=4r a required minimum?
No. That unsupported recommendation has been removed.
Does a positive closure margin prove a real treadle will work?
No. It only clears one geometric condition for an ideal in-line crank-slider.
References & Further Reading
- Wikipedia contributors. Treadle. Wikipedia
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