RC Motor Turns To Kv

With so many different ratings and specs, replacing your RC car’s motor can be expensive and confusing. This article will look at one of the more confusing aspects: turns vs. Kv.

Turns in an RC motor refers to the number of times the copper wire was revolved around the armature. A lower number means higher RPM. The Kv (not kV, as in kilovolt) refers to the actual RPM value while the motor runs without a load on one volt of electricity. Higher Kv means higher RPM.

The natural assumption would be that since higher Kv and lower turn ratings on your RC motor mean more RPMs, it’s best to get one with lower turns and higher Kv. 

That’s not always the case, though, since RPM is not a good indication of torque. 

We must understand how these ratings work and what they mean before getting the perfect motor for our RC car.

Turns Vs. Kv In A Brushless RC Motor

Before we can understand the impact that turns have on Kv, we need to know what each term means and its effect on the motor’s performance. 

Turns In An RC Motor

The turns rating literally refers to the number of times the copper wire is turned or looped around the motor’s armature. Commercial brushless motors range between ten and twenty-seven turns. This impacts the resistance inside the motor, with higher turn ratings meaning higher resistance.

In practical terms, the turn rating impacts the motor in two ways:

  • Lower turns mean more rotations per minute, so faster motors have lower turn ratings.
  • Higher turn ratings mean less speed but more torque. Though a higher turn rating motor won’t run as fast as one with a lower turn rating, the high turn motor will have more torque. High turn motors are helpful in heavier RC cars or rough riding conditions.

Minipro.com created a chart showing the average RPM generated by different turn ratings. Here’s a brief summary:

  • 3.5 turns: ± 10,500 RPM
  • 8.5 turns: ± 5,000 RPM
  • 21.5 turns: ± 1,800 RPM

Remember that these are only estimates and averages since other factors can also affect the actual RPM that you get from the RC motor.

Kv In An RC Motor

First, it’s crucial to note the difference between Kv, which we discuss here, and kV, which means kilovolts. These are two completely different concepts, even though they may be written the same. 

The Kv rating in an RC motor has to do with the motor’s constant (K) velocity (v). 

In everyday English, Kv refers to the number of rotations that an unloaded motor would do per minute while running on one volt of power. 

So a 1,000 Kv motor that’s unloaded (not powering anything else) would turn 1000 times per minute if it’s connected to a 1-volt power source.

You can now multiply that by the power you provide to get the actual RPM. 

For example, on a 9V battery, the motor stated above would turn at 9,000 RPM if it’s unloaded.

Turns Vs. Kv

The one factor that both turns and Kv have in common is the RPM. We’ve seen that a motor with fewer turns will have more RPM.

Your motor’s turns and its Kv rating have a negative correlation. 

A motor with high turns will have a lower Kv rating, while a motor with a higher Kv rating will have fewer turns. 

So, if you want more speed, you should go for high Kv, low turns. For more torque and less speed, go low Kv and high turns. 

Or, you can find a sweet spot somewhere in the middle, especially if you’re a beginner. It probably won’t win you any races, but you will have the best of both worlds to play around with.

What Else Affects The Kv?

The turns rating is a significant factor that affects the overall Kv of a motor, but it’s not the only factor. 

Here’s a summary of some other factors, apart from turns, that can affect the total Kv of a brushless RC motor:

Physical Size Of The Motor

Larger objects generally take longer to complete a rotation than smaller objects when the same amount of voltage is applied. 

So a larger motor will run at lower RPM than a smaller motor. This leads to a lower Kv rating in a physically bigger motor.

The Number Of Magnetic Poles

Electromagnetism is what makes a brushless RC motor run. The number of magnetic poles inside the motor will affect the RPM. A motor with a higher pole count will have a lower Kv value if all else is equal. For example, a 2-pole motor’s Kv would be considerably higher than a 4-pole motor if they have the exact turns count and the same voltage is applied to both.

Inrunner Vs. Outrunner Motors

Inrunner motors have a rotor spinning inside the motor’s case, while with outrunners, the motor’s casing itself rotates. 

Due to the size of the motor’s casing, outrunner motors tend to run slower than inrunner motors. 

In other words, an inrunner motor would have a higher Kv rating than an outrunner motor if all the other factors were equal.

Motor Quality

This should be logical, but a higher quality motor will usually perform better than a lower quality motor. 

Motors made from high-quality materials allow electricity to flow more freely and have better magnetic properties. 

All of this leads to improved performance and longer life for your motor.

All things being equal, a higher quality RC motor tends to have a higher Kv rating than a lower quality motor. 

Obviously, higher quality motors with high turn ratings will give better torque than lower quality motors with the same turn ratings.

Motor Winding Termination

When we talk about windings, we are still talking about the turns. 

Winding termination deals with how the copper wires used for the turns are terminated or connected to the power supply. 

There are two termination methods: the WYE or STAR wind and the DELTA wind. 

WYE wind termination leads to lower Kv ratings. In contrast, using DELTA wind termination in a motor gives it a higher Kv value.

Which Is More Important? Turns Or Kv?

If you’re trying to make your RC car go faster, higher Kv is generally preferable. 

Remember, though, that Kv is based on an unloaded motor. Once there’s a load on the motor, you won’t get the same RPM as an unloaded motor. Still, on average, higher Kv means more speed.

If speed is less important than the force applied, you’d be better to focus on a higher turn motor. Higher turn counts in a motor mean it can pull more weight, move larger cars, and traverse rough terrain more easily.

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