Brushless Motors

Brushless motors have almost completely replaced brushed motors in the RC industry. Their superior power and efficiency make them the obvious choice for powering your RC aircraft. Here’s what you need to know to use them, and some helpful info on how they work.

Brushless Motor Benefits

Before going into how brushless motors work, here’s why they’re useful:

More Efficient – Brushless motors are much more efficient than conventional brushed motors. This efficiency has been measured to be between 85% to 95% better than brushed motors.
Less electrical energy is wasted as heat, and more is used to do useful work.
Reduced Noise – Brushless motors have fewer mechanical parts than brushed motors, so they emit less sound.
Longer Lifetime – Fewer moving parts are in mechanical contact than in brushed motors, reducing wear.
Reduced EM Interference – Brushless motors emit less energy as electromagnetic (EM) waves than brushed motors do. This contributes to their efficiency, and helps reduce radio interference.
Torque, Voltage, And RPM Linearly Related – This means that the amount of torque or RPM produced by the motor divided by the voltage put in is a constant, making it easy to predict how much power you’re going to get.
How Brushless Motors Work

On a fundamental level, an electric motor’s only job is to convert electrical energy (like that provided by a battery) into mechanical energy, like the turning of a propeller or rotor blade. There are two basic facts that allow electric motors to work:

Electric and Magnetic Fields are Related - That is, every moving charge produces a magnetic field, and magnetic fields can produce electric charge.
Magnets Interact – Magnets will align when placed near to each other. All electric motors basically consist of two magnets. One of them is permanent, the other is a coil of wire that, when charged, becomes a magnet.
The motor is designed such that the magnetic fields produced by each of the magnets are always out of alignment, causing the motor axil to rotate. This is similar to what happens when you hold a permanent magnet to a compass – the compass swings position so that it lines up with the magnets field.

With the brushed motor design, the magnetic fields are kept out of alignment by turning on the different coils of wire that surround the motor axil in succession. Metal brushes make mechanical contact with the rotating axil and the contacts with each metal coil. As the axil rotates, the brushes contact different coils. The end result is that current flows through different coils at different times, constantly changing the magnetic field and rotating the motor shaft.

It’s here that we see the main problem with the brushed design: the contact between the motor coils and the brushes causes friction, which increases with speed. The metal coils wear out over time, and are prone to sparking. They can also ionize surrounding air, creating ozone. So how can we get around these issues? The answer lies in the brushless motor design. Instead of using mechanical brushes to turn on the various wire coils, an ESC (electronic speed controller) is used instead. The ESC switches the motor coils on or off rapidly, and is synchronized to the motor axil position.

Always look for an ESC with a capacity (measured in amps) greater than that of the motor you’re pairing it with.

Field Hours:

Lake Sawyer Hawks

Brushless Motors