Patent ID: 8345379

Claim:
A disk drive device comprising: a base member; a hub configured such that a double-sided recording disk is placed thereon; a read/write head configured to read and write in each of sides of the double-sided recording disk; a bearing unit configured to relatively rotatably support the hub against the base member; a core, fixed to the base member, configured to contain a circular part and a plurality of salient poles radially extending from the circular part; a three-phase coil formed in such a manner as to wind around the plurality of salient poles; a yoke fixed to the hub; and a magnet fixed onto an inner circumference of the yoke and radially facing the plurality of salient poles, the magnet being magnetized to drive P poles (P being an even number greater than or equal to 2) circumferentially, the hub including: a first external cylinder part extending axially, the first external cylinder part being fit to a central hole of the double-sided recording disk; a seating surface on which the double-sided recording disk is placed, the seating surface connecting to the first external cylinder part and extending in a radially outward direction; a second external cylinder part connecting to the seating surface and extending axially; and an extending part connecting to the second external cylinder part and extending in a radially outward direction, wherein when a non-rotating eigenfrequency of resonance in a secondary rocking mode with the double-sided recording disk placed on the hub is defined to be F0(Hz) and a rotational frequency of the hub is defined to be N (Hz), the eigenfrequency F0 satisfies a relation F0>N·(3·P+2), and wherein the base member includes a concave part surrounding at least a lower part of the second external cylinder part, and the extending part is located axially below an upper end of an inner circumferential end of the concave part.