In an ideal crank projection or Scotch-yoke relation, horizontal displacement is x=r cos(theta) and the full end-to-end stroke is 2r. This calculator compares that stroke for two entered radii.
Variable Throw Traversing Bar Interactive Calculator
Enter two crank radii. Results compare ideal 2r strokes, signed difference and percentage change—not a designed radius-adjustment mechanism, traverse guide, force or machine capacity.
Equation Used
- Each output is the ideal full range of x=r cos(theta).
- The two entered radii are compared independently.
- The two cases share display phase only; no live radius-change mechanism is solved.
- Pin-slot clearance, connecting rods, traverse velocity requirements, force, torque, friction, stress, wear, stops and safety are omitted.
Ideal Crank-Projection Comparison
NASA oscillatory-flow facilities document Scotch-yoke mechanisms for precise sinusoidal piston motion, while adjustable-stroke patents show that a physical variable throw requires additional guided or eccentric adjustment hardware. This calculator evaluates only two independent x=r cos(theta) cases.
What This Calculator Represents
The tool doubles each entered radius for full end-to-end ideal stroke, subtracts the first result from the second and reports that difference relative to the first.
Ideal Two-radius Stroke Comparison
x2=r2 cos(theta); stroke2=2r2
difference=stroke2-stroke1
percentage=100(difference/stroke1)
Worked Idealized Example
For r1=60 mm and r2=95 mm, the ideal strokes are 120 mm and 190 mm. The signed difference is 70 mm, or about 58.3% relative to the first stroke.
Model Boundary
- Calculated: two ideal 2r strokes and their signed arithmetic difference.
- Illustrated: two independent crank-projection or Scotch-yoke cases sharing phase.
- Not calculated: a radius-adjustment mechanism, connecting rod, traverse guide, cam law, velocity shaping, load, torque, friction, stress, wear, capacity or safety.
Frequently Asked Questions
Does this design a variable-throw crank?
No.
Why is stroke twice radius?
The ideal projection ranges from -r to +r.
Are the inputs automatically sorted?
No.
Does it calculate traverse speed or dwell?
No.
Are forces included?
No.
Can it size a winding or production machine?
No.
References
- NASA/CR-2007-215006: Scotch-yoke mechanism used for precise sinusoidal piston movement.
- U.S. Patent 2,867,134, Adjustable stroke crank: a guided wrist-pin block moves radially along a crank.
- U.S. Patent 4,261,228, Stroke adjustment for reciprocating mechanism: changing crank eccentricity requires a defined adjustment assembly.
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