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Motors - What does the term "Brushless Motor" mean?

Question: I see the term "Brushless" in some of the information about electric motors. What does this mean?

Answer: A tradional motor utilizes brushes to feed electricity to the armature (coils of wire) of the motor. The brushes physically brush up against the commutator (sometimes called a commutator "ring"). The commutator rotates with the armature and shaft while the brushes do not move. Various designs are used. Some commutators are split into segments and each time the brushes move over a different segment, different coils in the armature are "excited" by the electrical connection. Other designs use two or more continuous (non-segmented) commutator rings and alternate the current polarity and magnitude as the motor revolves through 360 degrees of rotation. Although simple and in spite of some very good material science work going into the composition of brushes over many decades of improvement, inevitably the brushes and commutator wear because they are in physical contact. Dust and contaminants in the air can accelerate this problem. Pitting due to electrical arcing can also occur particularly in high load, high current and/or high voltage situations. When the brushes wear down they must be replaced and eventually the commutator needs servicing as well. Often that is the end of motor because changing the commutator is an expensive process. Bottom line is that motors with brushes are wearing out from the first time they turn. It's just a matter of time. The plus side is that Brushed motors are easy to make, well understood, as common as dirt and hence generally cheap to manufacture.

A brushless motor is exactly what it purports to be... brushless! The magnets of a brushless motor rotate instead of the armature and hence the armature coils can be permanently wired up to the electrical feed. The rotating shaft is suspended in ball bearings and is never in direct contact with anything physical other than the bearings supporting the shaft. Brushless motors therefore last much longer, never need servicing (other than possibly bearings) and generally also produce more power more efficiently than a brushed motor of a similar size and weight. Unfortunately, in order to phase the current and time the excitation of the coils correctly, a brushless motor must rely on a sophisticated electronic controller made specifically for brushless motors. All of this sophistication, power, efficiency and longevity comes at a price... it costs more to make a brushless motor work properly than a brushed motor. You get more for your money but you gotta pay to get it! Bottom line here is that the brushless motor and the Lithium Polymer battery have together transformed electric model flying in a way that has not been possible before. It's not cheap but it works extremely well and for the first time we now have brushless motors, ESC's and LiPo's that when carefully matched up into a system, can give us performance and duration that was formerly only possible with glow or gas powered combustion engines.    

Article ID: 4812