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the model is as simple as this: I'd like to apply a torque to the Rotational Flange of a Revolute Joint.
However, the torque reaction should not be applied to the Support Flange of the Revolute Joint.
The torque reaction is indeed counterbalanced elsewhere and not in the Revolute Joint itself.
A real-world example is a vehicle wheel: the torque is given by a powertrain and transferred to the wheel by a shaft, so the torque reaction is not perceived on the wheelhub but on the powertrain mounts. enter image description here

So, none of the above seems to be correct:

  • in BLUE: there is a reaction on the Revolute frame_a that there shoudn't be. The support (white circle) seems to always balance the torque applied to the flange (gray circle)) but it doesn't make sense in this case;
  • in RED: there is no reaction on Revolute frame_a but there is no speed in the 1D line and this is not ok.

So, how can apply a Torque to a Revolute Joint without being forced to sense the counterbalanced torque directly on the joint?

Here the code

DarioMangoni
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  • I’m voting to close this question because it doesn't belong here – Graviton Feb 23 '21 at 14:06
  • @Graviton I'll be glad to move it where it belongs. Can you tell me a better place? – DarioMangoni Feb 23 '21 at 14:26
  • I asume that @Graviton wants to see this issue in https://github.com/modelica/ModelicaStandardLibrary. And yes, I also wondered, why the rotational axis of the revolute joint are implemented the way they are and not symmetically. – tbeu Feb 23 '21 at 19:28
  • Now available as https://github.com/modelica/ModelicaStandardLibrary/issues/3761 – tbeu Feb 24 '21 at 15:38

1 Answers1

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I came up with this solution that requires modifying the Revolute joint.
This is a minimal library with the modified Revolute Joint and a minimal example

Basically I just required that the torque on frame_a and frame_b is equal only along two directions orthogonal to the revolute axis (before they were equal along any direction).
And the torque called 'tau' provided by the auxiliary flange is applied along revolute axis direction only to frame_b, while for frame_a along this direction the torque is imposed to be zero.

This makes much more sense to me, but I'll be glad if someone proves me wrong.

As @tbeu just saw, I also sent an issue to the Modelica Standard Library GitHub, so it might be worth to wait for some official answer.

DarioMangoni
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