Use the Arkkio Torque Calculation node to define globally available torque variables for the selected domains, which is the air gap. Compared with the 
Force Calculation feature, the 
Arkkio Torque Calculation requires a much coarser mesh for the same accuracy. For a theoretical discussion, see the section 
Computing Forces and Torques.
 
    Enter a Torque name, which is then appended to global variables. This feature also gives access to the azimuthal and radial force density and magnetic flux density. The computed torque is made available as a global scalar variable with name 
<name>.Tark_<torque name>, where 
<name> is the 
Name of the physics interface.
 
    The Arkkio Torque Calculation node has to be used together with 
Continuity, 
Sector Symmetry, or 
Arkkio Extra Circular Boundaries features. The 
Arkkio parameters and 
Number of sectors default to be automatically retrieved in most cases. Otherwise, 
User defined options are available.