Hiscox movement 117 is a three-crank link connection: driven crank A, driving crank B and an elevated relief crank D have their moving pins joined by a triangular link. The relief branch preserves a kinematic constraint as the direct A-B link passes a dead-centre alignment.
Three Crank Link Interactive Calculator
Choose a schematic crank radius, relief-pivot height and crank angle. Outputs report the ideal equal-phase crank angles and translation of the rigid triangular link; no forces, tolerances or ratings are calculated.
Equation Used
- Fixed pivots A, B and D form a triangle, with D above the A-B line as in movement 117.
- The three cranks have equal radius and remain parallel in the ideal congruent-triangle construction.
- The triangular link is rigid and pin joints have zero clearance.
- Forces, torque, bearing load, interference, tolerance, deflection, speed and durability are omitted.
Driven, Driving and Relief Cranks
Gardner D. Hiscox labels A as the driven crank, B as the driving crank and D as a relief crank. The three moving crank pins are connected by a triangular link, while the fixed pivots also form a triangle.
Hiscox describes the direct link transmitting motion to a crank, with the relief crank providing an additional connection through the triangular link at dead centre.
What This Explanatory Calculator Does
With three equal, parallel cranks, the moving triangle is a translated copy of the fixed-pivot triangle. All crank angles remain equal and the triangle translation is the crank-radius vector.
This is a schematic kinematic construction. Hiscox does not supply sizes, materials, speeds, tolerances or application ratings for movement 117.
Ideal Congruent-triangle Construction
delta x = r cos(theta)
delta y = r sin(theta)
The entered relief height changes the displayed fixed triangle but not the ideal translation result. Equal crank radii and a rigid moving triangle are modeling assumptions made explicit here.
Worked Schematic State
For r = 40 mm and theta = 0 degrees, all three ideal crank angles are 0 degrees and the moving triangle is translated 40 mm in x and 0 mm in y. At 90 degrees, the translation becomes 0 mm in x and 40 mm in y.
These are geometry values, not manufacturing dimensions from Hiscox.
Model Boundary
- Historical arrangement: driven crank A, driving crank B, relief crank D and triangular link connections.
- Calculated: equal ideal crank phase and two components of rigid-triangle translation.
- Not calculated: force transmission at dead centre, torque, bearing reactions, link stress, pin clearance, crank mismatch, interference, inertia, balance, speed, lubrication, fatigue, tolerances, service life or suitability.
Frequently Asked Questions
Is this a three-axle side rod?
No. Movement 117 has two lower cranks A and B plus an elevated relief crank D joined by a triangular link.
Why is D called the relief crank?
Hiscox states that it is used with the triangular connections to avoid a dead centre.
Are the displayed dimensions historical?
No. The source provides no dimensions; radius and height are user-chosen schematic values.
Why do all three angles match?
That follows from the ideal equal-radius, parallel-crank, congruent-triangle construction.
Does the model calculate torque through dead centre?
No. It shows geometry only.
Can it set manufacturing tolerances?
No. The model assumes equal radii, a rigid triangular link and clearance-free joints. It does not calculate the effects of manufacturing variation.
References
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