what is the principle of brushless motor,how it works?

Answer 1

A conventional DC electric motor has a fixed magnet and a rotating wire armature. Power is fed to the rotating armature (a series of wire coils) via brushes and a commutator. The purpose of the commutator is to switch power with the correct polarity to the correct windings to make the armature rotate.

In the brushless DC motor, the armature is replaced by a rotating fixed magnet and the fixed magnet replaced by a series of windings or coils. Current of the correct polarity to cause the armature to rotate is fed to the correct windings (coils) using solid state switches and a position sensor. All brushes are eliminated and the electronics allows for accurate positional and speed control.

Answer 2

You didn't say what kind of brushless motor. The most common is the AC induction motor. The field coils induce a current in the armature (like a transformer) which creates the magnetic field in the armature. The interaction of that and the field coil's magnetic field turn the motor. All big motors are 3 phase induction motors, including in diesel trains engines.

Answer 3

Do a Google search for "step motor". A motor with noisy brushes is a Universal motor that the brushes hit the coil and causes noise. A Step motor is brushless and more quiet and rotates in steps.