RPM of Our Motor

Estimating the RPM of a Motor at 3.7V: A Quick Calculation

When working with small motors, it’s common to wonder how the motor will perform at a voltage that differs from the manufacturer’s given specifications. In this post, we’ll explore how to estimate the RPM (rotations per minute) of a motor when operating at 3.7V, based on the motor’s performance at 3.0V and 6.0V.

The Given Motor Specifications:

• At 3.0V: 4600 RPM, 15mA

• At 6.0V: 10000 RPM, 20mA

The key here is that the speed of a motor is typically proportional to the voltage supplied. This allows us to use a simple linear relationship between voltage and RPM to estimate the motor's speed at 3.7V.

1. Understanding the Voltage-to-RPM Relationship

Since the motor's speed increases in a linear fashion with the supplied voltage, we can calculate how much the RPM changes per volt by comparing the data at 3.0V and 6.0V.

• Voltage difference: 6.0V−3.0V=3.0V6.0V−3.0V=3.0V

• RPM difference: 10000 RPM−4600 RPM=5400 RPM10000RPM−4600RPM=5400RPM

This gives us a change of:

5400 RPM3.0V=1800 RPM/V3.0V5400RPM​=1800RPM/V

For every 1V increase in voltage, the motor’s RPM increases by 1800.

2. Estimating RPM at 3.7V

Now, let’s calculate the motor’s speed at 3.7V. We already know the motor runs at 4600 RPM at 3.0V. The difference in voltage between 3.0V and 3.7V is:

3.7V−3.0V=0.7V3.7V−3.0V=0.7V

Since the RPM increases by 1800 per volt, the RPM increase for 0.7V will be:

1800 RPM/V×0.7V=1260 RPM1800RPM/V×0.7V=1260RPM

Finally, we add this increase to the base RPM at 3.0V:

4600 RPM+1260 RPM=5860 RPM4600RPM+1260RPM=5860RPM

Conclusion

At 3.7V, the motor is estimated to spin at around 5860 RPM.

Factors to Consider

While this calculation gives us a good estimate, keep in mind that real-world factors such as motor efficiency, load, and wear could affect the actual RPM. However, this method provides a quick and easy way to get a close approximation of motor performance when using a different voltage than specified.