A brushed motor commutates mechanically, with brushes transferring current to a rotating commutator. A brushless motor commutates electronically, using position sensing to switch the windings. Brushed motors are simpler and cheaper to drive but wear at the brushes and generate dust and electrical noise. Brushless motors are sealed, longer lived and more efficient, and require drive electronics to function at all.

In specific circumstances. They are inexpensive, the drive is simple, and the relationship between voltage, current, speed and torque is easy to work with, which suits low-cost equipment, education and legacy machinery being maintained rather than redesigned. For new industrial designs, brushless is almost always the better choice on life, maintenance and environment grounds.

Periodic brush inspection and replacement, and attention to the commutator surface, which should be cleaned and occasionally skimmed. Brush dust is conductive and accumulates inside the motor and around it. Expect to plan brush changes as a maintenance item with a predictable interval, and rule the motor out where that access is difficult or where the dust cannot be tolerated.

A simple switching scheme that energises windings in fixed sequence based on coarse rotor position, usually from Hall-effect sensors. It is inexpensive and robust, but produces small periodic variations in output torque known as torque ripple. At speed the mechanical inertia smooths that out. At low speed and in applications requiring smooth motion or fine surface finish, the ripple becomes visible in the result.

When smooth motion at low speed matters, when the application demands fine positioning accuracy, or where torque ripple would show in the product, such as machining, printing or precision positioning. That is the rotary AC servo motor category. Where the requirement is simply controlled motion with moderate smoothness, trapezoidal brushless is cheaper and entirely adequate.

Generally not. Brush arcing is an ignition source, which excludes them from potentially explosive atmospheres without specific protection, and brush dust rules them out of cleanrooms, food production and optical or electronic assembly. Brushless motors have neither problem and are sealed, which is one of the main reasons the industrial market moved to them regardless of cost.

Brushless motors are more efficient, because there are no brush friction and contact losses and because permanent-magnet rotors avoid the rotor losses of induction machines. The difference is most noticeable in continuous duty and at part load, where it shows up as lower running cost and less heat to remove. Brush losses also increase as brushes wear and contact deteriorates, so brushed efficiency declines over the service interval.