Brushless motors have flooded the power tool market, but few builders have an in-depth understanding of how this revision in engineering can benefit their craft. Here’s a brief overview of where brushless motors came from and what they have to offer:
Although brushless motors are new to power tools, they’ve been used in industrial and manufacturing contexts since the 1960’s. It wasn’t until 2003 that Makita began incorporating the design into the line of power tools it supplied for the defense and aerospace industries. Since then, tools equipped with brushless motors have been appreciated for their improved performance and increased durability.
Traditional brushed motors are made up of a battery, metal or carbon brushes, a ring of magnets, an armature and a commutator.
When you initiate the motor, electric current travels from the battery, through the brushes and commutator and eventually ends up in the armature, which is basically just a bundle of wound copper wire suspended on an axle. The presence of electric current in these copper windings creates an electromagnetic field around the wires that causes them to start acting like a magnet (i.e. form a magnetically charged north and south pole). The bundle of copper wire is surrounded by the poles of permanent magnets in such a way that, once magnetized, it will rotate on its axle so that its north pole moves towards the permanent magnets’ south pole and vice versa. Because the armature rotates, it’s called the rotor. The permanent magnets don’t move relative to the motor, so they’re called the stator.
In a traditional motor, this is where the commutator and brushes come in: in order to manipulate the armature’s movement so that it constantly spins as opposed to just adjusting once to the polarity of the permanent magnets, the magnetic poles of the armature need to be consistently flipped at exactly the right pace. The commutator consists of a pair of plates on the armature’s axle that provide two connections for the armature’s copper coils. The brushes are two pieces of metal or carbon that make contact with the contacts of the commutator. The brushes provide consistent electron movement from either the positive or negative side of the battery supplying electric current. The commutator spins with the electromagnetic armature while the brushes remain stationary and positioned in such a way that every time the armature rotates to adjust to the permanent magnet’s polarity, the commutator connects with the brushes so that the polarity of the armature switches, prompting another polar adjustment, prompting another switch, and so on until you’ve got a consistently rotating, battery operated motor.
The design of traditional motors lend them to a variety of issues; the armature’s central position allows for sparking, electrical noise and overheating. The brushes limit the speed of the motor as well as how many poles the armature can have, plus they’ll eventually wear out.
Brushless motors became possible when someone thought to create a spinning motion by surrounding permanent magnets with the copper coils of an electromagnetic armature as opposed to having the armature rotate in the center. In brushless motors, the permanent magnets rotate and the electromagnets remain stationery (though their charge still flips). This design allows for a small circuit board to determine the flipping currents being sent to the armature, making brushes and commutators unnecessary.
There are a number of benefits that come with this revision: the copper windings’ placement outside of the motor configuration allows for them to be made larger in proportion to the magnets, which in turn creates the possibility for more power. Their outward position also allows them to cool down more effectively. The absence of the brushes and commutators limits the drag experienced by the spinning armature, making the motor’s energy use more efficient. Additionally, the use of a circuit board enables a direct connection between the electronics and the copper windings, so energy used correlates directly to the resistance the motor faces (meaning your drill will use less energy to drill through drywall than through mahogany). This also enables greater energy efficiency.
The downside? The addition of the electronic components of the circuit board make the brushless motor more expensive to manufacture. This cost is then passed on to the consumer. However, the net gain in efficiency and durability that comes with the design makes tools with brushless motors a cost effective choice for professional builders that use their equipment daily.