Integral balanced-moment head positioner

A balance-moment head positioner includes a rotor assembly which rotates about a central shaft. The rotor assembly supports at the same axial location a current-carrying coil, arms for the heads, and a counterweight such that the positioner is dynamically balanced with its center of gravity at the center of rotation. The coils are arranged with legs parallel to the central shaft on diametrically opposite sides of the assembly. In addition, the positioner includes magnets and an elongated U-shaped magnetic pole member with ends facing the coils at the same axial location at the arms. Thus the torque developed when current flows through the coil, and a reactive counter-torque developed by the rotating mass coincide, substantially eliminating all torsion in the shaft, and there is no net force on the shaft.