Hi Modelica Community,

I am developing a simple drive train model in which, in a first step, I wanted to integrate an easy transmission block. Gears should be shiftable, inertias and losses don't matter and so I came up with this idea:

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equation
  i = ecu_bus.transmission_simple_i;

  tau_a = flange_a.tau;
  tau_b = -flange_b.tau;
  phi_a = flange_a.phi;
  phi_b = flange_b.phi;
  w_a = der(phi_a);
  w_b = der(phi_b);

  w_b = w_a / i;
  tau_b = tau_a * i;
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Unfortunately this system doesn't behave the way I want it to. If I shift a gear between two rotating inertias, the ratio of the in and output velocity is changed, but no forces act, which is simply wrong.

Can I fix this problem somehow? Or is is simply wrong to set the derivates of a physical state in a relation?

Thanks for any help !

Cheers,
T