[Shaswat]

Hi @Hugo,

Super-elastic material (like Nitinol) has an elastic response when stress is applied to it. But I have been unable any library in SOFA to model it.

By “behaving as a rigid body” what I mean is that Nitinol has High Youngs Modulus (89GPa) and when I am using TetrahedronFEMForceField to model Nitinol, due to the high youngs modulus the backbone is not showing compliant nature.

I was wondering if there is any library in SOFA to model Super-elastic material or if there is a workaround to accurately model it.

Regards
Shaswat

[Shaswat]

There are two bodies. One is backbone passing through the center of the robot. Other is set of spacer disks. The tendons pass through the spacer disks.

I have been able to create a mapping between the disk and backbone using Barycentric Mapping. The mapping seems to be working but when I change the displacement of the tendons, I get erratic behavior in the robot. Is this because of the mapping or something else?

All the python scripts are in the GitHub repository.

Regards
Shaswat

[Shaswat]

Hi Hugo,

I am trying to create a mapping between my backbone and tendon disk so that when the cable actuates, both the bodies would move. That’s why I was using SubMapping. I will give Tetra2TriangleTopologicalMapping a try and see if it works. Do let me know if there is any another method to model a tendon driven robot.

Regards
Shaswat

[Shaswat]

Hi @suwan,

Could you share your entire scene file?

I am getting a segmentation error when I am implementing IndexValueMapper.

Here is my scene file –

<Node name="root" dt="0.01" gravity="0 0 0">
    <Node name="Disk1">
        <MeshGmshLoader name="DiskLoader" filename="Mesh/Robot1.msh"/>
        <TetrahedronSetTopologyContainer name="topo1" src="@DiskLoader"/>
        <TetrahedronSetGeometryAlgorithms template="Vec3d" name="container"/>
        <MechanicalObject template="Vec3d" name="obj1" showObject="1"/>
        <TetrahedronFEMForceField name="FEM" youngModulus="1000" poissonRatio="0.49" />
        <Node name="MeshROI" >
            <MeshObjLoader name="ROIloader" filename="Mesh/Spring.obj" translation="0 0 0" rotation="0 0 0"/>
            <MeshROI name="ROIm"
            drawROI="0"
            drawMesh="0"
            drawBox="0"
            drawEdges="0"
            drawTriangles="1"
            drawTetrahedra="1"
            drawOut="0"
            computeMeshROI="1"
            doUpdate="0"
            position="@../obj1.position"
            tetrahedra="@../DiskLoader.tetrahedra"
            ROIposition="@ROIloader.position"
            localIndices="1"
            ROItriangles="@ROIloader.triangles" />
            <VisualModel name="Visual" color="blue" />
        </Node>
        <IndexValueMapper name="ind_Out" indices="@MeshROI/ROIm.tetrahedronOutIndices" value="1e7" />
        <IndexValueMapper name="ind_Total" inputValues="@ind_Out.outputValues" indices="@MeshROI/ROIm.tetrahedronIndices" value="100" />
        <TetrahedronFEMForceField name="FEM1" youngModulus="@ind_Total.outputValues" poissonRatio="0.49" />
    </Node>
    
</Node>

Regards

[Shaswat]

@beichun could you share the .msh file you created. The msh file created by converting stl to msh using Gmsh is having some errors.

If you could share the file you created, it would be helpful.

Regards
Shaswat Garg

[Author]

Posts