Slotless spindle motor for disc drive

A disc drive data storage system, comprising:

• a housing;
• a central axis;
• a stationary member which is fixed with respect to the housing and coaxial with the central axis;
• a rotatable member which is rotatable about the central axis with respect to the stationary member;
• at least one data storage disc attached to and coaxial with the rotatable member;
• an actuator mounted to the housing;
• a head carried by the actuator for communicating with the data storage disc;
• an upper ball bearing assembly interconnecting the stationary member and the rotatable member;
• a lower ball bearing assembly interconnecting the stationary member and the rotatable member;
• at least one rotor magnet attached to the rotatable member;
• a back-iron supported by the stationary member;
• and
• a stator winding which is attached to the back-iron and has a slotless structure, wherein the rotor magnet, back-iron and stator winding have a common axial position along the central axis and have non-overlapping radial positions relative to the central axis and wherein the stator winding is magnetically coupled to the rotor magnet for rotating the rotatable member about the central axis and thereby moving the attached data storage disc relative to the head.