Calculator
Example Data Table
| Motor RPM | Motor Pulley | Driven Pulley | Center Distance | Slip | Estimated Driven RPM |
|---|---|---|---|---|---|
| 1750 | 4 in | 8 in | 24 in | 2% | 848.49 RPM |
| 1450 | 90 mm | 180 mm | 600 mm | 3% | 703.25 RPM |
| 1800 | 6 in | 3 in | 18 in | 1% | 3,564 RPM |
Formula Used
Pitch diameter: pulley diameter + belt thickness.
Driven RPM: motor RPM × motor pitch diameter ÷ driven pitch diameter × (1 − slip ÷ 100).
Reduction ratio: driven pitch diameter ÷ motor pitch diameter.
Motor torque: power in watts ÷ angular speed in radians per second.
Driven torque: usable output power ÷ driven angular speed.
Belt speed: π × motor pitch diameter × motor RPM ÷ 60.
Open belt length: 2C + π ÷ 2 × (D + d) + (D − d)² ÷ 4C.
Here, C is center distance. D and d are pitch diameters.
How to Use This Calculator
- Enter the motor speed in RPM.
- Enter motor and driven pulley diameters.
- Add belt thickness if you want pitch diameter correction.
- Enter center distance between the two shafts.
- Select the length unit used by your pulley data.
- Enter motor power, efficiency, service factor, and slip.
- Add a target RPM if you want the matching driven pulley size.
- Press Calculate and review the result above the form.
- Use the CSV or PDF button to save the calculation.
About Electric Motor Pulley Drives
An electric motor pulley drive links a motor shaft to a driven shaft. The belt carries motion between the two pulleys. A small motor pulley and a larger driven pulley reduce speed. The same setup raises torque at the driven shaft. A larger motor pulley and a smaller driven pulley increase speed. This calculator helps you compare those choices before parts are ordered. Recheck all values after installation. Record the final setup for future maintenance and troubleshooting.
Why Pitch Diameter Matters
Real belts do not ride at the outside edge of the pulley. They bend around a pitch line inside the belt. For quick design work, adding belt thickness to pulley diameter gives a useful pitch estimate. This improves speed, belt length, and ratio checks. It also makes small pulley comparisons more realistic.
What The Results Mean
Driven RPM shows the final shaft speed after slip is applied. Speed ratio shows how much the drive changes speed. Belt speed helps you judge whether a belt is running too slowly or too fast. Input torque is motor shaft torque. Output torque estimates the driven shaft torque after efficiency losses. Design power multiplies motor power by the service factor. Use it when the machine starts often or sees shock loads.
Good Setup Practice
Use measured pulley diameters when possible. Keep the center distance larger than half the diameter difference. This gives a valid open belt path. Check the wrap angle on the smaller pulley. Low wrap can cause slip and heat. Also check belt maker limits for speed, minimum pulley size, and power rating. This page gives planning values. Final selection should follow the belt supplier chart and the machine safety rules.
Useful Design Notes
Small changes in pulley size can create large speed changes. Always confirm the desired driven RPM. Then compare the required driven pulley diameter with available stock sizes. If the calculated size is not sold, choose the nearest size and recalculate. Keep guards, alignment, shaft load, and tension in mind. A quiet drive usually has correct alignment, proper tension, and enough belt contact.
FAQs
What does this calculator estimate?
It estimates driven RPM, pulley ratio, belt length, belt speed, torque, wrap angle, and required driven pulley size for a target speed.
Why is belt thickness included?
Belt thickness helps estimate pitch diameter. The belt rides around a pitch line, not only the pulley outside diameter.
What is pulley reduction ratio?
It is the driven pitch diameter divided by the motor pitch diameter. A higher value means lower driven speed and higher torque.
How does belt slip affect RPM?
Slip lowers the driven shaft speed. A two percent slip means the calculated driven RPM is reduced by two percent.
Can this be used for V-belts?
Yes, it can support early V-belt planning. Final belt choice should follow the belt maker rating chart.
What is service factor?
Service factor adds a margin for shock, frequent starts, long use, or uneven loads. It raises the design power value.
Why is center distance important?
Center distance controls belt length and wrap angle. A short center distance can reduce contact and increase slip risk.
Is the torque result exact?
No. It is an estimate from power, speed, and efficiency. Real torque also depends on belt tension and machine load.