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Gear Ratio and RPM
The relationship between gear ratio and RPM is straightforward: output speed equals input speed divided by the gear ratio. A 3:1 gear ratio reduces a 3600 RPM motor to 1200 RPM at the output shaft while tripling the available torque. This speed-torque tradeoff is the fundamental purpose of gear systems.
RPM conversion is critical for matching motors to loads. Electric motors operate most efficiently at their rated speed, but loads often require different speeds. Gearboxes bridge this gap, allowing a high-speed motor to drive a low-speed, high-torque application efficiently.
RPM Conversion Formula
Motor Speed Reference
| Motor Type | Speed (RPM) | 3:1 Output | 10:1 Output |
|---|---|---|---|
| 2-pole AC (60Hz) | 3600 | 1200 | 360 |
| 4-pole AC | 1800 | 600 | 180 |
| DC servo | 3000 | 1000 | 300 |
Frequently Asked Questions
How do I choose the right gear ratio?
Divide the motor RPM by the desired output RPM. If your motor runs at 1800 RPM and you need 300 RPM, you need a 6:1 ratio. Also verify that the motor's torque multiplied by the gear ratio provides enough output torque for your load, accounting for gear efficiency losses.
Can I use gears to increase speed?
Yes, by making the driving gear larger than the driven gear (ratio less than 1:1), you get speed multiplication. However, output torque decreases proportionally. This is called overdrive and is used in vehicle transmissions for fuel-efficient highway cruising.