KEVOS® MAKEOS · Power Transmission
V-Belt or Flat Belt Drive Design
How many belts does this drive need, how long are they, and what load do they put on the shafts?
Design of an open belt drive: driven pulley size and speed, belt speed, exact pitch length, wrap angle, tension ratio from the friction coefficient and groove angle (Euler), design power with service factor, centrifugal tension, tight and slack side tensions, the number of belts for an allowable tension per belt, and the resultant shaft load.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Power | kW | Power to transmit. |
| Driver speed | rpm | Speed of the driving pulley. |
| Driver pitch diameter | mm | Pitch diameter of the driving pulley. |
| Speed ratio (driver ÷ driven speed) | Driver speed ÷ driven speed (above 1 reduces speed). | |
| Centre distance | mm | Distance between shaft centres. |
| Service factor | Service factor for the driver and driven machine. | |
| Belt | choice | V-belt (wedging in a 38° groove) or flat belt. |
| Friction coefficient | Friction coefficient between belt and pulley. | |
| Belt mass per metre | kg/m | Mass per metre of one belt. |
| Allowable tight-side tension per belt | N | Allowable tight-side tension of one belt (from the belt maker’s rating). |
Method and formulas
- d₂ = d₁ × ratio; v = π d₁ n₁ ÷ 60,000; φ = asin[(d₂ − d₁) ÷ 2C]; length = 2C cos φ + π (d₁ + d₂) ÷ 2 + φ (d₂ − d₁); wrap = 180° − 2φ.
- Tension ratio e^(μ′θ), with μ′ = μ ÷ sin 19° for V-belts.
- Effective pull F_e = P × SF ÷ v; centrifugal tension T_c = m v²; belts n = ⌈F_e e^(μθ) ÷ (e^(μθ) − 1) ÷ (T_max − T_c)⌉.
- Shaft load = n √(t₁² + t₂² + 2 t₁ t₂ cos 2φ) with t = belt tension less centrifugal tension.
- Example: 7.5 kW at 1450 rpm on a 125 mm pulley needs 3 belts of 1,704.9 mm.
Limitations
- Uses an allowable tension per belt rather than the maker’s power rating tables; check with the belt catalogue.
- Open drive with two pulleys.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Design a V-belt drive for a motor and driven machine
- Check the shaft and bearing load from belt tension
- Decide whether to add a belt or enlarge the pulleys
Who it is for
- Design engineers
- Maintenance engineers
- Power transmission engineers
What you get
- Driven pulley, belt speed, length and wrap
- Tensions and number of belts
- Shaft load
Interpreting the result
- Larger pulleys raise belt speed and cut tension, often saving a belt.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2487–2536. Topic reference; no source tables or recommended settings are reproduced.
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