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.