You can't drive motors arbitrarilt slowly with standard ESCs, they rely on back EMF for commutation and slow
speed means the back EMF signal fades into the switching noise.
Since HDD motors are usually 4-wire Y connected, it might be simpler to drive them unipolar, as if a 3-phase
stepper. 3 channels from an ULN2003 or ULN2803 might be suitable if the current isn't too great.