Motors with brushes and commutator are inexpensive but require a lot more maintenance than brushless motors. The brushes erode and fail, create friction, impede current and decrease efficiency. The advent of motor controllers has driven a strong and steady market shift toward brushless motors. Brushless motors require another method of current commutation. Hall devices are cheap but not very accurate, and are usually used with a position encoder increasing cost and BOM count. Resolvers are very accurate and durable but very expensive. Encoders with commutation output have become dominant because they are very accurate, already required in many cases for position feedback, and the cost is competitive.