Relation between Minimal Speed and Rotational Inertia of Stable PM Maglev Bearing Rotator

The authors’ former works demonstrated that a passive magnetic (PM) rotator supported merely by PM bearings has a minimal speed, above which it can stabilize its equilibrium, under the function of a so-called Gyro-effect. It is unclear, however, by which factors is this minimal speed determined. To investigate the effect of rotor inertia on minimal speed, three same rotors made of different materials were manufactured: rotor A was made of plastic and its rotary inertia is 6.293×10-5 (kg·m2); rotor B was made of aluminum and its inertia is 1.074×10-4 (kg·m2); rotor C was made of steel and its inertia is 2.081×10-4 (kg·m2).The rotors were tested in a model with PM bearings and the maximal eccentric distance of the rotors was measured. In case the maximal eccentric distance of the rotor was smaller than the gap between the rotor and the stator, the rotor could be considered being suspended. In such way the minimal speed for stable levitation of the rotor A, B and C was obtained to be 4597, 3030 and 2222 rpm respectively. It concluded that the minimal speed increases with the square of decreasing inertia according to a formula: [y=1/(a+bx+cx2), here y: minimal speed, with unit rad/s; x: rotational inertia, with unit kg·m2; a, b, c are constants: a=3.5367×10-5,b= 39.1012,c=-8.8726×104].