What is "hysteresis drag torque" on PM motors?

Altair Forum User

Submitted by Joe on Tue, 04/24/2012 - 18:49 

With respect to the Motion BLDC block: Is 'Rotor shaft Coulomb Friction Magnitude' equal to 'Hysteresis Drag Torque'? The spec sheet has a value called 'Hysteresis Drag Torque' that has the same units (Nm) as Rotor shaft coulomb friction.

Altair Forum User

Submitted by Duco Pulle on Tue, 04/24/2012 - 21:39.

When you rotate a permanent magnet motor there will be magnetic field reversals in the stator and with such reversals there will be hysteresis loss, which appears as a 'hysteresis drag torque'. This is very small and typically on the order of the Coulomb friction torque. However, the rotor friction is typically independent of rotor speed, but the hysteresis drag is proportional to speed so can become more of a factor at high (>5000) RPMs.