Struggling with FixingBox for Constraining Mechanical Model in SOFA

[sodasoda520]

Hi

I am a beginner in using SOFA and I am currently learning how to add fixed constraints to a mechanical model in my simulation. I have been trying to use FixingBox, but I haven't been able to get it to work as expected. I followed some tutorials and tried to use FixingBox to apply fixed constraints to certain areas of my model, but the model still moves freely in the simulation instead of being fixed.

Here is the code snippet I am using:

from stlib.scene import Scene
from fixingbox import FixingBox

def createScene(rootNode):
    scene = Scene(rootNode, gravity=[0.0, -9810.0, 0.0], plugins=["SofaSparseSolver"])
    rootNode.dt = 0.01

    # Graphic modelling of the legends associated to the servomotors
    scene.Config.createObject("MeshSTLLoader", name="loader", filename="data/mesh/blueprint.stl")
    scene.Config.createObject("OglModel", src="@loader")

    elasticbody = rootNode.createChild("ElasticBody")
    elasticbody.createObject('GIDMeshLoader',
                             name='loader',
                             filename="data/mesh/tripod_high.gidmsh")
    elasticbody.createObject('TetrahedronSetTopologyContainer',
                             src='@loader',
                             name='container')
    elasticbody.createObject("MechanicalObject",
                             name="dofs",
                             position=elasticbody.loader.position,
                             rotation=[90.0, 0.0, 0.0],
                             showObject=True,
                             showObjectScale=5.0)
    elasticbody.createObject("UniformMass", totalMass=0.032)
    elasticbody.createObject("EulerImplicitSolver")
    elasticbody.createObject("SparseLDLSolver")
    elasticbody.createObject("TetrahedronFEMForceField",
                             youngModulus=800,
                             poissonRatio=0.45)

    # Visual model
    visual = elasticbody.createChild("Visual")
    visual.createObject("MeshSTLLoader",
                        name="loader",
                        filename="data/mesh/tripod_mid.stl",
                        rotation=[90, 0, 0])
    visual.createObject("OglModel",
                        src="@loader",
                        name="renderer",
                        color=[1.0, 1.0, 1.0, 0.5])

    visual.createObject("BarycentricMapping",
                        input=elasticbody.dofs.getLinkPath(),
                        output=visual.renderer.getLinkPath())

    # Adding FixingBox to constrain part of the mechanical model
    fix = FixingBox(rootNode,
                    elasticbody.ElasticMaterialObject,
                    translation=[0, 0, 0],
                    scale=[30., 30., 30.])
    fix.BoxROI.drawBoxes = True

As shown above, I used FixingBox at the end of the code to apply fixed constraints to certain areas of the model. However, no matter how I adjust the translation and scale parameters, the object in the simulation is still not fixed.

I have a few questions:

What is the correct usage of FixingBox? Am I making a mistake somewhere?
Are there other methods available in SOFA to apply fixed constraints to a mechanical model?
Is there a better way to apply fixed constraints to specific areas of a mechanical model in SOFA?
I would greatly appreciate any help or guidance from the community. Thank you very much!

[epernod]

Hi,

you can use a SelectEngine like BoxROI, SphereROI, etc.. to select the area of points you want to fix and then give the input to your FixedConstraint.
You can check an example here: https://github.com/sofa-framework/sofa/blob/master/examples/Component/Engine/Select/BoxROI.scn

Best regards

[sodasoda520]

thank you for your patience for such a small question

[hugtalbot]

Hi @sodasoda520
you should also consider reading the associated documentation : https://sofa-framework.github.io/doc/components/engine/select/roi-selection/

[sodasoda520]

Thanks @hugtalbot
I am working on a project where I rigidify a part of a deformable object to connect it with an end effector. After successfully completing the rigidification of the control part, I encounter the following errors when running the animation and pressing the Shift key:
[ERROR] [MechanicalObject(MousePosition)] Invalid vOp operation 1 (null(V_DERIV),0(0),null(V_DERIV),40)
[ERROR] [MechanicalObject(MappedMousePosition)] Invalid vOp operation 1 (null(V_DERIV),0(0),null(V_DERIV),40)
These errors occur before I import the end effector. Could you please provide insights on the potential causes of these errors and any recommended solutions?
Thank you for your assistance.