For brushed DC motors, we know that graphite brushes are necessary for robust applications that may feature forward-reverse operation or higher current loads. Typically with such applications, the motor selected will also feature ball bearings. In addition to being opportune for higher radial and axial loads, you typically will select this bearing option for start-stop operation.
Just as with precious metal brushes, sintered sleeve bearings are suitable for continuous operation. This option is typically more cost effective, but is not fitting for higher loads, ambient temperatures less than -20°C, and vacuum environments.
Moreover, the life of a brushless motor (EC), is typically dependent on the life of the bearing system within it. All standard maxon EC motors feature preloaded ball bearings. If a ball bearing is preloaded, an additional load is administered axially to the bearing to reduce the amount of excessive play, which could cause an increased amount of vibration and noise.
If you have questions past this brief summary, experienced Sales Engineers across the globe are awaiting your call. If you are unsure of who contact, please visit our website at http://www.maxonmotor.com/maxon/view/content/contact.