Brushed v Brushless - 4QD - Electric Motor Control

Brushed v Brushless

We’re often asked to talk about brushed v brushless motors so here goes…..[we’ll put some pictures in here in due course but for now it’s just words].

Brushed motors have been around for ages, they are;

  • Simple – put a voltage across them and off they go.
  • Cheaper.
  • Less efficient – typically around 75%.
  • Noiser, both physically and electrically.
  • Brushes will wear out over time – typically 1000 – 3000 hours.

Brushless motors on the other hand tend to be;

  • More efficient due to less friction – around 90%+.
  • Quieter, both physically and electrically.
  • Longer lasting – typically 10 000 hours.
  • Able to run at higher speeds.
  • But – they need a more sophisticated controller to make them move.

So why do brushless motors need a more complicated controller? In a brushed motor as the armature rotates, the brushes and commutator switch the voltage between the successive windings, making in effect a mechanical switch. In a brushless motor this mechanical switch is not there and thus the switching has to be done electronically by the controller. To do this switching the controller needs to know about the position and speed of the armature, it can get this information either from Hall sensors on the outside of the motor or by sensing the voltage induced in the stator coils [sensorless mode].

Multiple motors. A controller for a brushed motor does not care how many motors are connected to it so long as the overall current rating is not exceeded, our current record is a single controller driving eight motors. But this does not apply for brushless controllers, because the controller needs to know about the position of the armature a single controller can only drive a single brushless motor. Note, there are dual channel brushless controllers that can drive two motors, but the general principle that you cannot just add motors in parallel to an existing controller still holds true.

Motor types. A brushless controller needs to be told quite a lot about the motor it is working with e.g. inductance, resistance, pole pairs, threshold speed etc. This is not the case with brushed.

Regenerative braking. For a brushed motor regen braking is relatively easy and done by quite straightforward switching within the controller. But with brushless motors more sophisticated measurement and switching is required, and our experience is that regen is difficult to do well without significant investment in software.





Categories: Miscellaneous

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