Lately there has been a lot of talk in the power tool world about brushless motors. While the technology isn't new to tools, it has recently gained traction due to some high-profile releases by Makita, Milwaukee, DeWalt, and others.
"Brushless motors have been around since the 1960s, being used in industrial and manufacturing applications for [motors that drive] conveyor belts," says Christian Coulis, cordless product manager for Milwaukee Tools. However, Makita was the first company to use them in power tools. "[It was] first in our assembly division in 2003 for the defense and aerospace industries," says Wayne Hart, Makita's communications manager, "and then again in 2009 when we released a brushless three-speed impact driver."
Manufacturers claim that brushless tools have added performance and durability and that they're smarter than the average tool. So what exactly is the technology behind these new motors?
How Old-School Brushed Motors Work
A traditional brushed motor is made up of four basic parts: carbon brushes, a ring of magnets, an armature, and a commutator. The magnets and brushes are stationary, while the armature and commutator rotate together on the motor shaft within the magnets.
When the motor is energized, a charge travels from the battery, through the brushes, and into the commutator. (The brushes are spring-loaded to maintain physical with the commutator.) The commutator then passes the charge on to the armature, which is made up of copper windings (they look like bundles of copper wire). The windings are magnetized by the charge and push against the stationary ring of magnets that surround it, forcing the armature assembly to spin. The spin doesn't stop until the charge from the battery stops.
How Brushless Motors Work
A brushless motor loses the brushes and the commutator. And the locations of the magnets and windings are reversed: The magnets are on the conventional motor shaft and the copper windings of the armature are fixed and surround the shaft. Instead of brushes and a commutator, a small circuit board coordinates the energy delivery to the windings.
Because the electronics communicate directly with the stationary windings, the tool adjusts according to the task—which is why the companies market these as "smarter" tools. For example, if you're using a brushless drill to drive screws into Styrofoam, it more readily senses the lack of resistance (compared with a brushed motor) and begins to pull only what little charge it needs from the battery. If the tool then starts putting 3-inch screws into mahogany, it will adjust accordingly and draw more current. By contrast, a brushed motor will always run as fast as it can while in use.
In addition, brushless motors can be more powerful overall. Because the copper windings are on the outside of the motor configuration, there is room to make them larger. Brushless motors also don't have the friction and voltage drop that brushes create by dragging against the spinning commutator. This physical results in a continuous energy loss during the operating process.
The net gain is a tool with greater efficiency and more durable motors. So it goes without saying that every power tool will have a brushless motor in it by the end of the year, right? Not a chance, Milwaukee's Coulis says.
"While the benefits of brushless technology are vast, manufacturers encounter extreme cost barriers due to the added cost of the motor and electronics that it takes to manage the motor properly," she says. In other words, they're expensive, and so brushless motors are better suited to benefit pros who can shell out the big bucks for a tool that they're going to use every day. Brushless tools are approximately 30% more expensive to make than standard cordless tools, and the batteries to power them are typically out of reach for most DIYers. But as battery technology improves and tool design advances, buyers will start seeing more and more brushless tools at their local home center.
Brushless motors are here to stay, but it will probably be a while before the technology filters down to all power tools for weekend DIYers.