Brushless gear motor has some advantages as same as DC brush motor and remove brush and commeuetor to make no mechanical contacts. Magnets are rotate instead of motor coil.
Semiconductor (hall elements or hall IC) and driver board detect rotor position then changes current to the motor coil to run the brushless motor.
Technical theory of brushless gear motor is as same as DC brush motor up to BLI and Law of left hand of Fleming then. The basic characteristics are same but just different rotate magnet or coil.
Brushless motor is classified two type from the view point of construction, one is inner rotor type (magnet is located inside of coils) which has better mobility and the other is outer rotor (magnet is located outside of coils) which is better to make thinner type motors.It is necessary to choose for each application from both types of brushless motors.