This information is part of the Modelica Standard Library maintained by the Modelica Association.

This is a model of an ideal stiff coupling: One device connected to the coupling is turning clockwise (looking at the shaft end), the other device connected to the coupling is turning counter-clockwise (looking at the shaft end). The torque at flange_b has the same magnitude as the torque at flange_a but opposite sign. This is achieved by using an ideal gear with ratio = -1.

Variable w represents the angular velocity of flange_a and tau represents the torque transferred from flange_a to flange_b.

This behaviour is essential when coupling electric machines. The usage is demonstrated in the example Modelica.Electrical.Machines.Examples.DCMachines.DCPM_Drive.