For active components such as micro motors the torque
depends on the control of the micromotor and its type. For
example, a synchronous motor uses the principle of a rotating
magnetic field dragging a permanent magnet at the same
speed. The torque is then a fimction of the phase angle between
field vector of the rotating field and the field vector
of the permanent magnet, the so-called load angle. One possibility
to assess a synchronous motor or a stepper motor is
to keep the rotor shaft at zero speed and let the field vector
rotate at a small speed. Then a figure torque versus phase
angle can be traced which gives the