Our first step in building an RC car is to choose a suitable brushless motor. For best performance, you need to know more. What is the difference between 3000Kv and 4000Kv? This is a fairly typical problem. If you are interested in this, then the following knowledge about motors will be useful to you.
What does Kv mean?
The speed of the RC brushless motor is usually expressed by the Kv value. The unit of Kv is RPM/V, which means that for every 1V increase in voltage, the number of revolutions (RPM) of the no-load motor in one minute.
Formula: RPM = Kv X Voltage. If the maximum voltage supported by the motor is 8.4v (2s), then the speed of a 3000Kv motor at 8.4v (no load) is 25200RPM.
3000Kv vs 4000Kv, which is better?
4000Kv with higher revs is not necessarily better than 3000Kv. Because different Kv values apply to different vehicles or equipment, you need to see if it is suitable for your powertrain, such as ESC and battery, etc. In general, high Kv is used for small-scale cars, while low Kv is used for large-scale cars.
| Motor | 3000Kv | 4000Kv |
| Rotating speed | Lower | Higher |
| Torque | Higher | Lower |
| Horsepower | Smaller | Bigger |
| Size | Bigger | Smaller |
Rotating speed
The higher the Kv, the higher the motor speed. However, many people mistakenly believe that a high Kv motor provides a faster vehicle speed, which is not the case. The top speed of the vehicle depends on the combination of battery, Kv, and gear ratio (drivetrain). So with the same powertrain, replacing a higher Kv motor doesn’t necessarily result in a higher travel speed. Example: A car running 3000rpm/v 2s is about the same as a car running 2000rpm/v 3s. All choices are compromises.
Torque and Size
The size of the motor is closely related to the Kv. Generally, a wider motor provides higher torque but a lower Kv value, so can be equipped with larger tires (or propellers); while a small and long motor has a higher Kv value and a lower Kv value Torque, so suitable for small tires (or propellers). So in practice, larger motors run at lower RPMs, while smaller motors run at relatively higher RPMs.
How to choose a brushless motor?
There are many types of brushless motors on the market. The first thing you need to check is whether the size of the motor and the position of the mounting holes are suitable for the car. Kv or RPM are not the only parameters to consider when choosing a motor. In addition to it, you also need to consider torque and voltage, and so on. For example, high torque is very important for a large proportion of cars. If the motor cannot provide enough torque, the driving speed will be slower. Also, you need to pay attention to whether the motor is suitable for the powertrain, like the voltage.
In simple terms, 30k RPM is a typical range of motor speeds and is the best choice. If you want to know more about RC brushless motors, check out another article (RC Brushless Motor Size Chart). It lists the relationship between motor speed, turns, voltage, and related applications.