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Brushless DC Motor


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I prefer the AC stuff myself. The following is some information I stumbled accross whilst 'surfing the net' earleir today.


A brushless DC motor is a motor without brushes, slip rings or mechanical commutators connected to the windings. In a brushless motor, the rotor, which has permanent magnets, rotates and the stator, which has the windings, is stationary. Commutation is controlled electronically.




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The brushless DC motors I'm familiar with actually resemble AC motors! The motor body consists of a permananent magnet rotor, usually manufactured using 'rare earth' materials such as cobalt composites rather the more common ferrite based permanent magnet material. This provides an extremely intense (scary!) magnetic field that is largely uneffected by temperature / shock etc.


The rotor is usually highly balanced, supported by precision (high speed) bearings and is surrounded by a stator, usually with (wait for it.....) three phase windings!


The whole box and dice is driven by an 'inverter' controller, usually with embedded uP control with low loss / high current MosFet drivers. Older technology controllers relied on hall effect sensors to monitor rotor position and provide 'timing' for the controller, more advanced types rely on 'sensorless' control whereby the stator windings themselves provide feedback.


The performance of these motors can be astounding!. For example, samples weighing 500g producing around 1Hp at ~30,000RPM are available. These types are designed for low Voltage (ie 8-12VDC@30-80A) 'special' applications such as aeromodelling and similar.


I understand that the recent NASA Mars Rover was driven by brushless motor technology similar to the above. Hi Tech, High Performance, High Price:o





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  • 5 weeks later...
It took me awhile to notice that specs for brushless motors don't list starting current. One (perhaps not-so-obvious) benefit of electrical commutation being that the drive can use power switches (MOSFETS) rated only just above continuous running current - the downside being less starting torque...
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  • 8 years later...

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