KEVOS® MAKEOS · Mechanics
Windlass, Gear Hoist and Differential Pulley Effort
What effort lifts this load with a windlass, geared winch, rope block or differential chain pulley?
Effort and mechanical advantage for the handbook’s simple lifting machines: wheel and axle, a windlass driven through up to two gear pairs, a block and tackle with several parts of rope, a differential chain pulley and a Chinese (differential) windlass, with an overall efficiency.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Machine | choice | Choose the lifting machine. |
| Load to lift | N | Weight to be lifted. |
| Crank, hand-wheel or large sheave radius | mm | Wheel-and-axle wheel or crank radius; for the differential pulley and Chinese windlass, the larger sheave or drum radius. |
| Drum or small sheave radius | mm | Drum radius; for the differential pulley and Chinese windlass, the smaller sheave or drum radius. |
| Gear ratio, first pair (driven ÷ driver) | Speed reduction of the first gear pair. | |
| Gear ratio, second pair (1 = none) | Speed reduction of the second gear pair. | |
| Parts of rope supporting the load (block) | Number of rope parts carrying the moving block. | |
| Crank radius (Chinese windlass) | mm | Radius of the crank turning a Chinese windlass. |
| Overall efficiency | % | Overall efficiency from friction (differential pulleys are low, which keeps them self-sustaining). |
Method and formulas
- Wheel and axle: F = W r ÷ R. Geared windlass: F = W r ÷ (R × gear ratios).
- Block and tackle: F = W ÷ n.
- Differential pulley: F = W (R − r) ÷ 2R. Chinese windlass: F = W (R − r) ÷ 2 × crank; the load rises half the difference of the drum circumferences per turn.
- Effort with friction = ideal effort ÷ efficiency.
- Example: a 10000 N load on a differential pulley of 150 and 135 mm needs 1,428.6 N.
Limitations
- Static lifting; acceleration and rope stiffness are excluded.
- Use certified lifting equipment within its rated load.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check the hand effort on a chain block or winch
- Compare hoisting arrangements for a lift
- Estimate hook travel per turn of a hand wheel
Who it is for
- Rigging supervisors
- Maintenance fitters
- Machine designers
What you get
- Effort required
- Mechanical advantage
- Load travel per turn or per unit of effort travel
Interpreting the result
- A differential pulley with low efficiency holds the load without a brake; check that the chosen machine is self-sustaining if it must be.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 170–171. Topic reference; no source tables or recommended settings are reproduced.
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