Brushless AC servo motors and stepper motors have long life spans, which are largely due to the lack of wearing components. Unlike brush type motors, other than the bearings, brushless AC servo motors and stepper motors have no wearing components. Additionally you do not have conductive brush dust, which, as it collects on the commutator, may short the armature. The radial and axial loading requirements of step and servo motors are based upon the shafts of the motor, which are usually far less than what the bearings are designed to handle, which provides for a healthy motor life span. However, occasionally motors do need to be repaired. Either a feedback device goes bad, or some kind of electrical mishap may cause the drive to provide too much current, which may damage the winding, or it could be as simple as the bearing grease drying up.