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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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superman on 9 Sep 2020
Dear, sir. I am doing biped walking simulation by Matlab2017b。 When i use four sphere to plane contact models on flat foot of the biped robot, the biped flied off the ground at the beginning of simulation, as shown in the attachment. The robot mass is 74 kg. The contact sphere radius is 0.01 m. The contact stiffness and damping are 90000 and 4000. Could you give me some advices? Thanks very much. I am looking forward to your reply.

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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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More Answers (4)

Ramkumar Natarajan
Ramkumar Natarajan on 5 Sep 2020
In the newer versions of Simulink, the setting is in Modeling > Model Settings instead of Simulation > Model Configuration Parameters


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