Cordless Hammer Drills & Impact Drivers: Comparison Test
Cordless drills and impact drivers already bore more holes and drive more screws per battery charge than we once thought possible. But there's always room for improvement, the big development in cordless tools has been brushless motors.
All cordless tool motors consist of an outer stationary magnet surrounding an inner spinning magnet. In a traditional motor, the outer magnet is a conventional type and the inner is an electromagnet with energized windings of copper wire. A brushless motor reverses that—it has an outer electromagnet and an inner conventional magnet. This setup does away with the carbon brushes used to convey electric current to the electro magnet; instead it uses a microprocessor circuit.
Without brush friction and electrical resistance losses, the brushless motor is highly efficient and does more work per unit of current than ordinary motors. It's analogous to a better engine helping a car get more mpg. In our test of brushless impact drivers and rotary hammers, we drove screws, bored holes, and came away amazed and the tools' capacity. Here's our report.