3421A Oriental Motor Sensorimotor

The Oriental Motor / Seiberco Sensorimotor Brushless 2-Phase, Permanent Magnet Synchronomous Motors is driven with a sinusoidal current wave form, so some people refer to it as an AC motor. The stator has 24 salient poles, individually wound. The rotor carries 18 hard magnetic magnets, (SmCo, or Nd-Fe-B), therefore, the motor has 9 electrical cycles per mechanical revolution compared to the typical hybrid stepper with 50 electrical cycles and the typical BLDC with 2 to 4 cycles per revolutions.

The magnetic macrostructure (stator flux pattern due to PMMMF) indicates three diagonal axes of symmetry, dividing the motor into six elementary "motors operating in series". Therefore, the motor can be completely evaluated by the analysis of the torque components acting on four consecutive stator poles. This plot was made using a Linear Finite Element Analysis Program. As in other PM BLDC motors, as well as in hybrid steppers the cogging or detent torque on the shaft is the sum of the elementary torque components due to PM's only. They tend to be quite high and need to be meticulously balanced. The periodicity of those components is twice the frequency of the electrical cycles since the direction of the torque is a function of the absolute flux in the airgap. The magnitude is approximately seven times the rated output torque of the motor.