KEVOS® MAKEOS · Power Transmission
Open Belt Drive Geometry
What speed, wrap and pitch length follow from this pulley layout?
Calculate ideal speed ratio and exact geometric belt pitch length for two circular pulleys in an open drive.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Driver pitch diameter | mm | Effective pitch diameter, not pulley outside diameter. |
| Driven pitch diameter | mm | Effective pitch diameter on the output shaft. |
| Centre distance | mm | Distance between the parallel shaft axes. |
| Driver speed | rpm | Input pulley speed. |
Method and formulas
- Let r and R be smaller and larger pitch radii, C the centres and a = asin((R−r)/C).
- Exact ideal pitch length = 2 × sqrt(C²−(R−r)²) + π × (R+r) + 2 × a × (R−r).
- Small-pulley wrap = 180° − 2a in degrees. Output RPM = input RPM × driver diameter / driven diameter.
- Belt speed (m/s) = π × driver diameter × RPM / 60000. Example 100/200 mm at 500 mm centres gives about 1476.243 mm pitch length and 750 rpm output from 1500 rpm.
Limitations
- Open, coplanar, no-slip drive only; no idlers, belt stretch or crossed drive.
- Pitch length is not necessarily the manufacturer’s outside or datum length. No power rating is calculated.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- pulley ratio
- belt length
- belt speed
Who it is for
- Designers
- Maintenance technicians
What you get
- Geometric pitch length
- Small-pulley wrap
- Ideal output speed
- Belt speed
Interpreting the result
- Select a catalogue belt and recheck centres, tension, wrap and supplier service factors.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2484–2487. Topic reference; no source tables or recommended settings are reproduced.
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