Measurement of the head-to-disk stiction force in an unmodified hard drive using external Hall-effect sensors

A key parameter in the design of magnetic disk drives is the start-up motor torque needed to guarantee a spin-up. We present a detailed discussion of a method to measure motor start torque in the drive and to relate it to head-disk stiction. Our method involves controlling the total current applied to the motor during start attempts, and using externally mounted magnetic field sensors to detect disk rotation. In this way we are able to determine the torque required to cause the heads to break-free of the disks