• Brushless Motors

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    This page will provide information on how the brushless motors used in R/C models work.

    A brushless motor looks a lot like a brushed motor that has been turned inside out. The magnets are attached to the armature instead of the can and the windings are attached to the case instead of the armature. In operation your magnets spin and not your windings.

    As shown in the figures below, the rotor has permanent magnets mounted to it and is supported by a pair of ball bearings. These are the only moving parts in the motor and are also the only parts to wear out. Compare this to a brushed motor with its brush and commutator interface wear areas.

    The stator or armature is made up of a laminated stack and wound with copper windings. Magnetic sensors detect the angular position of the rotor with respect to the stator. These sensors tell the controller (ESC) which loop needs to have the current on and which ones need the current off. This allows the motor to produce a continuous torque in one direction.

    What are the Advantages?

    • Less radio interference since there is no brush arching
    • Less resistance in the windings since there is no brush to commutator interface. Additionally you can have thicker wires (lower resistance) than a brushed motor of equivalent size. Both of these result in overall lower resistance and higher efficiency and torque.
    • Lower friction loss since there is no spring/brush pressure and drag on the commutator.
    • They are efficient over a much wider range of power. Efficiencies range from 75% up to nearly 90% depending on style/brand.
    • Better cooling since the heat generating windings are against the outer case and not buried inside.
    • No springs to change, no brushes to replace, no commutator to cut.

    Sensorless or Sensored?

    The two categories of brushless motors and controllers are sensored and sensorless. These two categories refer to how the armature location is determined (sensed) and then controlled.

    A sensored motor (ie Aveox and Novak), you set the motor to a fixed timing to match your specific setup, just as you do with a brushed motor. These motors have small sensors, typically 3 at 120 degree intervals, which determine and communicate the rotational position of the armature. The controllers and motors often need to come from the same manufacture to work correctly.

    The speed controllers for sensored motors can be less expensive to manufacture since they do not need to perform any motor monitoring. The down side is that the motor is more expensive because it must have the sensors built into it. These sensors can be fragile and they take up valuable space inside the motor.

    A sensorless motor (ie Hacker, Lerner) is just as its name implies. These motors do not contain any sensors and instead leave the determination of armature position to the speed controller.

    The Sensorless controllers are more complicated since the controller has to compensate for the lack of sensors in the motor. It does this with added programming and hardware to deal with various magnetic fluxes which occur in BL Motors. Sensorless theoretically allows you to run more efficiently at all throttle settings compared to a sensored setup.