Abstract: A power tool is provided including a brushless motor having a stator defining a plurality of phases and a rotor. A power unit is provided including power switches operable to deliver power to the motor. A primary controller is interfaced with the power unit to output drive signals to drive the phases of the motor over a series of sectors of the rotor rotation. The primary controller measures a back-electromotive force voltage of the motor and transitions motor commutation from the present sector to the next sector based in relation to the back-EMF voltage. A second controller is provided to receive at least one of the drive signals, calculate a speed and/or direction of rotation of the motor from the drive signals, and take corrective action to cut off supply of power to the motor if it detects an overspeed condition or incorrect direction of rotation.

Abstract: A power tool is provided including a brushless motor having a stator defining a plurality of phases and a rotor. A power unit is provided including power switches operable to deliver power to the motor. A primary controller is interfaced with the power unit to output drive signals to drive the phases of the motor over a series of sectors of the rotor rotation. The primary controller measures a back-electromotive force voltage of the motor and transitions motor commutation from the present sector to the next sector based in relation to the back-EMF voltage. A second controller is provided to receive at least one of the drive signals, calculate a speed and/or direction of rotation of the motor from the drive signals, and take corrective action to cut off supply of power to the motor if it detects an overspeed condition or incorrect direction of rotation.