KEVOS® MAKEOS · Mechanics
Traction Hoist Check (Counterweight, Rope Tension Ratio, Sheave Traction, Motor Power)
For a counterweighted lift or hoist driven by rope traction on a grooved sheave, will the ropes grip without slipping loaded and empty, and what motor power does it need?
Check of a counterweighted traction drive: the counterweight from the car mass and a share of the rated load, the rope tensions on each side with the car full and empty, increased for acceleration, their ratio, the traction the sheave can give from the groove friction and wrap (as the belt friction tool, with the groove angle), and the motor power from the largest out-of-balance load, speed and efficiency, against the motor fitted.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Car (platform) mass | kg | Mass of the car or platform, its frame and its share of the ropes. |
| Rated load | kg | Rated load. |
| Counterweight balance (share of rated load) | % | Share of the rated load the counterweight balances (40–50% is usual). |
| Acceleration or braking | m/s² | Largest acceleration or emergency braking deceleration. |
| Sheave | ||
| Rope-to-groove friction coefficient | Friction between the rope and the sheave groove. | |
| Wrap angle | ° | Angle of rope wrap on the sheave. |
| Groove included angle (0 = round seat) | ° | Included angle of a vee or undercut groove (0 for a round seat). |
| Drive | ||
| Rated speed | m/s | Rated rope speed. |
| Drive efficiency | % | Efficiency of the motor, gearing and sheave. |
| Motor power fitted | kW | Rated power of the motor. |
Method and formulas
- Counterweight = car + balance × rated load.
- Tensions = mass × g on each side, with the heavier side × (g + a) ÷ g and the lighter × (g − a) ÷ g; ratio = heavier ÷ lighter, full and empty.
- Traction available e^{μ′θ} with μ′ = μ ÷ sin (groove ÷ 2) (as the belt friction tool); motor power = largest out-of-balance × g × speed ÷ efficiency.
- Example: counterweight 850 kg; ratios 1.4332 full and 1.5689 empty against 2.5056; motor 3.5024 kW.
Limitations
- Rope and compensation weights, and car friction in the guides, are not included.
- Static and acceleration traction; buffer impact and safety gear cases are separate.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check traction on a goods lift or hoist
- Choose the counterweight balance
- Check motor power for a counterweighted drive
Who it is for
- Lifting engineers
- Design engineers
- Maintenance engineers
What you get
- Counterweight and rope tensions
- Tension ratios against the traction available
- Motor power
Interpreting the result
- Balancing about half the rated load keeps the ratio about the same full and empty, which makes the best use of the traction.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 165–168, 2473–2490. Topic reference; no source tables or recommended settings are reproduced.
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