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What Does KV Mean for Brushless Motor?
Is a higher KV rating better? Why some small KV motors better than the higher one, how does this work? Is the KV related to motor speed? A lower KV will rate faster? What's the mystery of KV? Now, let me explain to you what KV represents.
KV refers to the rpm constant of a motor - it is the number of revolutions per minute that the motor will turn when 1V (one Volt) is applied with no load attached to the motor. In summary, we call it revs per volt - but do not think you will obtain those revs when you attach a propeller; obviously the revs will be reduced because of the load.
Higher RPM motors tend to generate less torque, to get within a usable power band you have to gear down which compromises some of that RPM. Higher torque motors that are geared up for better top end. For all out speed runs the higher kV setup would be the best bet. Typically, something in the middle will provide the best drivability.
What does the KV tell us? Well, it is related to the power out from a motor, or more usefully the torque level of a motor. It is determined by the number of winds on the armature (or turns as we sometimes call it) and the strength of the magnets - you see, there are so many variables with electric motors. So KV allows us to get a handle on the torque we can expect from a particular motor.
So, we may get the answers.
Is a higher KV rating better?
No, no KV is better, but different KV can be better for certain situations. Lower KV means more torque and less top speed and High KV is the opposite.
Why some small KV motors better than the higher one, how does this work?
This one is same as the one above.
Is the KV related to motor speed?
Yes. First, let's take an example. A 2650KV 4S (14.8V) motor compare with a 2200KV 6S (22.2V) motor. Which one is faster? As KV=RPM/volt, so we can get the motor speed easily. RPM=KV*volt, so the speed of a 2650KV motor is 39220 RPM (2650Kv * 14.8v = 39220 RPM). Similarly, the 2200KV motor is 48840 RPM (2200Kv * 22.2v = 48840 RPM). In additional, a higher KV motor is faster on the same voltage as well.
A lower KV will rate faster?
The answer is NO. High KV motor would be used to give high power for short bursts in competition gliding, but the lower KV motor has more torque and is better suited to most application.
Brushless DC Motor
As a new RC enthusiast, you may not familiar with brushless DC motor. A brushless DC motor is also known as electronically commutated motor. It is a synchronous motor and powered by a DC electric source via an integrated inverter/switching power supply. Thus, it can produce an alternating current (AC) electric signal to drive the motor.
Develop
Since 1962, brushless DC motors have been in commercial use, but it appeared almost 76 years later than brushed motors. A brushless motor comes with a permanent magnet synchronous motor, uses one or more Hall Effect devices to sense the position of the rotor, a permanent magnet external rotor, three phases of driving coils, and the associated drive electronics.
Some limitations of brushed motors can be overcome by brushless motors. Brushed DC motors develop a maximum torque when stationary, linearly decreasing as velocity increases. Provide higher efficiency and a lower susceptibility of the commutator assembly to mechanical wear. These benefits come at the cost of potentially less rugged, more complex, and more expensive control electronics.
Parameters
There are two parameters indicate the performance of a brushless DC motor: motor voltage constant KV and motor torque constant Km. As my previous article mentioned, KV refers to the rpm constant of a motor - it is the number of revolutions per minute that the motor will turn when 1V (one Volt) is applied with no load attached to the motor.
Then what's about Km?
Km defines the ability of the motor to transform electrical power to mechanical power and is a valuable tool for the application engineer particularly for recommending a “best fit” replacement for a competitors motor.
Don't overlook these two parameters. Km = Kt/√Rt - where Kt is the torque sensitivity (oz.-in./amp) and Rt is the terminal resistance (ohms). As can be seen from the above equation, the lower the motor’s resistance the higher the Km will be. For beginner, it is hard to decide which motor is properly as there are so many specifications are listed. At this time, if you use the equation for calculating the motor constant, then you can make a relatively good recommendation.
What can we get benefits from brushless motor?
Brushless motors are widely used in industrial applications, computers and home electronics, as well as electric. If you’re a RC racing enthusiast, you may know that brushless motors are very popular among RCers and they are a very important company.
A brushless motor has better performance and suffers less wear than brushed motors on similar size. Although it appears relatively late to brushed motor and much more expensive, but brushless motors have displaced brushed from many applications.
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