Brushless motors explained: what does KV actually mean?

Anyone delving into electrically powered RC models will soon come across terms such as KV, watts, amps and ESC. Especially if you want to build your own power system, all these figures can be a bit confusing at first.

In this blog, we’ll look at some of the basic concepts behind a brushless setup.

What is a brushless motor?

A brushless motor operates without the carbon brushes found in traditional brushed motors.

Brushless motors are efficient, powerful and low-maintenance. As a result, they’re now used in virtually every category of the RC hobby.

What does KV mean?

In simple terms, a motor’s KV rating indicates how many revolutions per minute the motor theoretically aims to achieve per volt when running unloaded.

A 1000 KV motor will therefore attempt to achieve a higher speed at a given battery voltage than, for example, a 500 KV motor.

However, this does not automatically mean that a motor with a higher KV rating is also more powerful.

KV and propeller size

KV must always be considered in conjunction with the battery voltage and the load on the motor.

For aeroplanes, the general rule is:

• A lower KV is often combined with a larger propeller.
• A higher KV is often combined with a smaller propeller.

A larger propeller or one with a higher pitch can draw significantly more current. It is therefore important to follow the manufacturer’s recommendations.

What does the ESC do?

The ESC, or Electronic Speed Controller, controls the brushless motor.

The ESC must be capable of handling sufficient current for the chosen motor and propeller combination.

For example, you should not combine a setup where the motor can draw 50 amps with a controller that can handle a maximum of 30 amps.

More cells mean higher voltage

LiPo batteries are often designated by the number of cells:

• 2S: two cells in series
• 3S: three cells in series
• 4S: four cells in series
• 6S: six cells in series

The more cells there are, the higher the nominal voltage of the battery pack.

A motor operating at a higher voltage can therefore achieve a much higher speed. That is why you should not simply switch from, say, 3S to 6S without checking whether the motor and speed controller are suitable for this.

To measure is to know

When you’re putting together your own power system, a wattmeter is an extremely useful tool.

It allows you to check how much current and power the setup is actually using.

This allows you to check whether the motor, ESC and battery remain within their safe operating limits.

It’s the whole combination that counts

With an electric drive system, it’s all about the combination of:

• Motor
• KV value
• Battery voltage
• Propeller
• Speed controller
• Battery

Changing a single component can affect the rest of the setup.

Are you unsure about the right combination for your model? At Aerobertics, we’re happy to help you choose a suitable power system.