Brushless RC Motors for Radio Controlled Airplanes

Brushless RC Motors along with LiPo battery packs have leveled the playing field
between electric and nitro powered flight!

Looking for a Brushless motor?
Check out Hobby People's selection!

Most folks in our hobby once stereotyped electric RC airplanes as cheap toys or weak little parkflyers. Brushless RC motors and Lipo Packs have turned this hobby upside down making electrics the model airplane of choice! You may be wondering what makes brushless motors so much better than standard brushed motors previously used with RC airplanes.

You may be wondering why you can't use the same electronic speed controller with both types of RC airplane motors. Perhaps you're curious why brushless motors have three wires instead of two?

What the heck is the difference between inrunner and outrunner RC airplane brushless motors. Which type would be best for your next radio controlled airplane? What are the Most Popular Brushless Motor Manufacturers?

If you're interested in knowing the answers to these questions along with other basic facts regarding brushless RC motors, then read on!

Difference between Brushed and Brushless RC Motors
Advantages of Brushless Motors
Inrunner vs. Outrunner Brushless Motors

This page also addresses some of the common questions regarding brushless motors such as wiring, electronic speed controllers, Torque vs. Speed, along with the basic fundamentals of gearbox and propeller selection.

Brushed vs. Brushless RC Motors

To fully appreciate the advantages of a brushless RC motor, you need to have a basic understand of how motors work.

"How Stuff Works” has an in depth explanation of how motors work, and the graphics in the section were taken from that article. Below is a quick summary of how a canned motor works.

Standard "canned" Motor

A standard brushed motor is often referred as a canned motor. Every canned motor consists of the following parts:

Armature- The rotating portion of the motor. It consists of the poles, terminals, and the commutator.

Poles- Copper wires wound around a piece of metal forming an electromagnet. The poles are attached to the armature. Most motors have 3 or more poles

Terminal- Point at which the copper wire of a poll attaches.

Commutator- A switch on the armature that reverses the current to the poles every 1/2 rotation so that the magnetic fields of each will always maintain rotation.

Brushes- Tabs in the motor cap that are wired to the battery and make contact with the plates on the commutator as the armature rotates.

Magnets- The outer shell (or can) of the motor is lined with two permanent magnets, of opposite polarity. This non-rotating portion of the motor is also referred as the motor stator.

The battery is wired directly to the brushes. The brushes make contact with the plates of the commutator as the motor turns. There are the same number of plates on the commutator as there are poles on the armature.

When the brushes come in contact with the appropriate plates of the commutator, a particular pole (electromagnet) is charged. When a pole is charged, it is attracted to one of the magnets in the can and repelled by the other.

The commutator acts as a switch by switching the polarity of each pole every time the pole passes a magnet. When the polarity is switched, the pole is attracted to the next magnet in the can while being repelled by the one it just passed. This process repeats as long as power is supplied to the motor.

Disadvantages of Brushed Motors

The brushes and commutator wear out
The brushes and commutator must be cleaned periodically
Friction from the brushes slow the motor down
Friction from the brushes lead to shorter flight times and battery life.
Friction from the brushes cause lower power to weight ratio

How brushless motors work

Brushless RC motors work on the same principle as brushed motors, except the electromagnets(poles) are stationary and the permanent magnets are on the spinning portion of the motor.

Since the electromagnets are stationary, there is no need for brushes! The electronic speed controller(ESC) takes care of switching the voltage of the electromagnets.

It's important to know that a brushless speed controller and a brushed speed controller can not be used interchangeably. They perform completely different tasks.

The quickest way to tell the difference between a canned motor and a brushless motor is to count the number of wire leads. All brushless RC motors have 3 wires. Canned motors have 2 wires. The third wire is used for feedback. Switching any two of these wires will change the rotation of the motor.

Advantages of Brushless Motors

No brushes or commutator wear out
Don't have to worry about cleaning the brushes or commutator.
There's no Friction from brushes to slow the motor down.
Longer flight times and extended battery life due to the absence of friction from brushes.
Much higher power to weight ratio!

Inrunner vs Outrunner

There are two types of brushless RC motors for RC airplanes. The permanent magnets of inrunner brushless motors are positioned on the inside of the electromagnets.

Inrunner brushless motors are set up very similar to the canned motor explained above, except the permanent magnets and electromagnets are in opposite positions.

An outrunner brushless motor has the permanent magnets on the outside of the electromagnets. You can see in the picture to the right that the outer hub holding the permanent magnets has the output shaft attached in the center.

Inrunner Brushless Model Aircraft Motors

The faster a motor spins, the more efficient it is. Inrunner motors turn very fast and are much more efficient than outrunner motors. Inrunner brushless RC motors require a reducing gearbox between the motor and propeller of your RC airplane. For this reason, the output speed and torque of the propeller can easily be "tweaked" to facilitate different flying characteristics by using different size gears.

The downside is added parts that can and do fail. The gears get stripped, and the gearbox shafts are easily bent. It can also be an obstacle when mounting the gearbox motor combination for your RC airplane neatly, especially under a cowling.

Outrunners	Inrunners

Low RPM's, high torque Less efficient than inrunners No gearbox required Narrow prop selection Silent	High RPM's, low torque More efficient than outrunners Require a gearbox Wide prop selection Noisy

Understanding Motor Specifications

Most electric airplanes either come with a motor or the manual will tell you exactly what size motor it needs. If you're converting from a brushed motor or glow engine to a brushless RC motor, understanding what these designations mean will be important.

Voltage Constant

Kv is the "Voltage Constant". This is how many RPM's the motor turns for each volt applied. Actually, it's a tad less because even brushless motors aren't 100% efficient.

For example, if you apply 12volts to a 200Kv motor, it will turn at just under (12 x 200) 2400 RPM's.

Torque Constant

Kt is the "Torque Constant". For all motors, Kt= 1355/Kv. You'll have to ask someone smarter than me where the 1355 comes from, cause I don't have a clue! Just accept it for what it is.

In a nut shell, this means the faster the motor spins for a given voltage (Kv), the lower the output torque will be (Kv).

Outrunners generally have a lower Kv, which in turn produces more torque at a slower speed for spinning those larger props. The opposite is true with inrunners.

No Load Current

Io is the "No Load Current". This is the amount of current it takes to spin the motor with no prop.

For example, if your motor is pulling 25Amps, and the Io is 2Amps, then you really only have 23Amps turning the prop.

Terminal Resistance

Rm is the "Terminal Resistance". This is the internal resistance of the motor measured in Ohms. The higher the Rm, the less efficient the motor is.

Current and Power

The maximum current and power is what determines how large of a prop and what size plane can be used with the motor. Simply multiply the current by the battery voltage to get power.

The larger the propeller's diameter and pitch, the more current the motor will draw for a given RPM. For example, the 200Kv motor will run at 2400 RPM's regardless of whether it has a 10x6 prop or a 11x5 prop. But, the 11x5 prop will cause the motor to draw more current. Drawing too much current will destroy the motor.

Brushless Motor Manufacturers

Below is a working list of some of the more common brushless RC motor manufactures. At the bottom of each listing, there is a comments section for sharing your thoughts, experiences, or questions with each of these brands.

It seems like every day there is a new brand of brushless motor hitting the market. If you have experience with another quality manufacturer of brushless airplane motors, Add it to the list!

Working List of Popular Brushless RC Motor Manufacturers

Feel free to ask questions or add comments!

Emax Brushless Motors Emax Brushless Motors are designed and manufactured by the Chinese company Yinyan Model Tech .

There are currently four different models of Emax ...

Electrifly Brushless Motors Electrifly Brushless Motors are top-of-the line quality motors. Electrifly is a division of Great Planes Great Planes Model Manufacturing, one of the ...

E-Flite Brushless Motors E-Flite has a solid reputation for being on the leading edge of electric powered flight technology. E-flite has a wide selection of electric RC airplanes ...

AXI Outrunner Brushless Motors AXI brushless motors are very efficient high quality outrunner motors manufactured by Models Motors in the Czech Republic. Since all AXI motors are ...

Brushless Motors on eBay

Are you looking to buy a brushless motor? Brushless RC motors cost a bit more than standard brushed motors, but are well worth the extra money. Many times you can minimize that cost increase by finding good deals on eBay.

Determine what size you need by reading the specifications that come with your airplane. Brushless motor and ESC combo's are also common on eBay and can save you some cash.

Take a look at what's available by click view all at the bottom of each box below. Many of these ship from around the world, so make sure you look at the cost for shipping. But even after taking shipping costs into consideration, you can usually save quite a bit by shopping around on eBay.