Extracting forces in specific axes

[eddychen06]

@hugtalbot When extracting forces, is it possible to get the force in a specific axis. If so, how would it be implemented with python?

[hugtalbot]

Hi @noteddeh

welcome on SOFA GH discussion 🙌 !

If you mean the forces applied to a object in collision (with constraints) with another one, this thread explains it.

If you mean the internal and external forces, this thread should be the explanation.

If by forces, you mean something else, could you detail it please?

[hugtalbot]

Hey @noteddeh
The values are rendered by arrows in the ConstantForceField.
Else if you want to access it, the forces are the python array named "forces"

Best

[eddychen06]

Just to make sure, each array in the forces array is a point/indice?

[hugtalbot]

Each array is a constraint (in your case a contact point). This contact may affect 1 point of your object or several points if you have a mapping between your mechanics and your collision representation

[SangbaekYoo]

Dear @hugtalbot,
I try to measure the force. I think that the formation of "constraint = self.rootNode.Cube.collision.MechanicalObject.constraint.value" is now different in v24.12. Should I modify many things of this example code to apply in the latest version?

[904288343]

@SangbaekYoo I have the same question. Have you solved yet?

[DanteAngio8]

Hi @hugtalbot
I have a question about extrating internal and external forces. In the discussion forum you post, it seems like we can extract internal forces through the force property in MechanicalObejct. However, since I am using Lagrangian constraint (LCPConstraintSolver), the force property is filled with zero. Right now I am able to extract the contact/collision force between two object using the method from https://www.sofa-framework.org/community/forum/topic/getting-forces-generated-by-a-collision/#post-14171, I am wondering is there a way to also extract internal forces? (eg. I want to know the force on the end point of a beam when its tip hits a wall)

[hugtalbot]

this is another topic (here we talk about contact forces when using the Lagrange multipliers constraint resolution).
If my reply does not answer you, please @DanteAngio8 open a new topic ;)

[shizi-19]

Hi Hugo, @hugtalbot @DanteAngio8 @eddychen06

Thanks for you reply and time spent!

I have checked you post "How to access the contact forces when using constraint resolution based on Lagrange multipliers #3812", but I still have issues.

Your code extracts the constraint direction at each raw of constraint output, (for example, pointID =index+2, constraint_x = index+3, and etc ).
However, if there are two DoFs that are sit under the same constraint (like you line 0 or 1 or 2), the results would be incorrect. (I checked the PointID and it saves constraint direction into itself if nbConstraint = 2.

Besides, we get one constraint force, but if we have nbConstraint = 2, which constraint direction should we multiply the force intensity (constraint force)?