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Rigidly connected port error with Simscape Multibody Contact Forces Library

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Adding blocks from the Simscape Multibody Contact Forces Library to a new model gives the following error message:
"External Force and Torque External_Force_and_Torque_PlaB has its follower port rigidly connected to the world frame; it has no effect. You can configure this diagnostic in the Simscape Multibody Configuration Parameters dialog."


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Accepted Answer

Sebastian Castro
Sebastian Castro on 23 Jan 2018
Edited: Sebastian Castro on 7 Feb 2018
This error is due to a default setting with new Simulink models, which is incompatible with the Contact Forces Library.
To resolve this:
  1. Go to Simulation > Model Configuration Parameters
  2. In the Simscape Multibody > Diagnostics pane, change the "Rigidly constrained block" diagnostic to "warning" or "none"
For those interested the details: The Contact Forces Library blocks uses "External Force and Torque" blocks to apply contact forces/torques to both bodies in contact. If at least one of these bodies is rigidly connected to the World Frame, you will get this error based on the diagnostic setting above. This error essentially warns you that you're applying a force to a body that will not move regardless of the applied force.
- Sebastian


Jacob Valadez
Jacob Valadez on 3 Apr 2020
But then how can I apply a force to an object? Do all the bodies have to be connected to the world frame? I'm simulating a pendulum mounted in a car and I want to make the car move thought a rail. Can you tell me how I can use the force and torque block in order to make move the car and the pendulum?

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