Attaching the parts in the softrobot.

[ndolphin-github]

Hello.
I have a problem attaching two different models in the scene.
Currently, I am using SOFA v 23.06 in python environment and I tried to apply the example code to my situation. The code I was following is the example in the Softrobot plugins -- Tripod robot. This is the part where I am confused and cannot figure out.

def __attachToActuatedArms(self, numstep):
        rigidParts = self.RigidifiedStructure.RigidParts
        for arm in self.actuatedarms:
            arm.ServoMotor.Articulation.ServoWheel.addChild(rigidParts)
          
        rigidParts.addObject('SubsetMultiMapping',
                              input=[self.actuatedarms[0].ServoMotor.Articulation.ServoWheel.getLinkPath(),
                                     self.actuatedarms[1].ServoMotor.Articulation.ServoWheel.getLinkPath(),
                                     self.actuatedarms[2].ServoMotor.Articulation.ServoWheel.getLinkPath()],
                              output='@./', indexPairs=[0, 1, 1, 1, 2, 1])

Above is the code lines in the step4-3.py in the Tripod examples. I am trying to attach the rigid frame and three pneumatic actuators which is the typical shape of the soft manipulators. So in my case, three ServoWheels are just replaced to three actuators. I am not sure how to correctly use the SubsetMultiMapping in my case since this keeps showing the error.

I tried to write similar to the example and this is my code.

def Tripod(name="Tripod"):

    def _rigidify(self):
        groupIndices = []
        frames = []
        deformableObject = self.UpperFrame.MechanicalModel
        for i in range(0,3):         
            box = addOrientedBoxRoi(self, position=[list(i) for i in deformableObject.dofs.position.value],
                                 name="BoxROI" + str(i),
                                    translation=vec3.vadd(translations_boxROI[i],[56,0,0]),
                                    eulerRotation=[angles[i]*180/math.pi,0,0], scale=[5, 30.5, 30.5])
            box.drawBoxes = True
            box.init()
            groupIndices.append([ind for ind in box.indices.value])
            frames.append(vec3.vadd(translations_boxROI[i],[56,0,0]) + list(Quat.createFromEuler([angles[i]*180/math.pi,0,0], inDegree=True)))
 
        rigidifiedstruct = Rigidify(self, deformableObject, groupIndices=groupIndices, frames=frames,
                                    name="RigidifiedStructure")
        return groupIndices , frames
    
    def __attachToActuatedArms(self):
    
        rigidParts = self.RigidifiedStructure.RigidParts
        for arm in self.actuatedarms:
            arm.addChild(rigidParts)

        rigidParts.addObject('SubsetMultiMapping',
                             name="mapping",
                             input=[self.actuatedarms[0].tetras.getLinkPath(),
                                    self.actuatedarms[1].tetras.getLinkPath(),
                                    self.actuatedarms[2].tetras.getLinkPath()
                                    ],
                             output='@./', indexPairs=[0, 1, 1, 1, 2, 1 ])      
         
    self = Sofa.Core.Node(name)
    self.actuatedarms = []
    ## ============ variables for robot position =================## 
    D1 = 30*math.sqrt(2)
    D2 = 29*math.sqrt(2)
    youngModulusFingers = 5000
    youngModulusStiffLayerFingers = 1500 
    radius = 50
    Actuator_loc = [[0,0,0], [0, radius*math.sqrt(3), 0], [0, radius/2*math.sqrt(3), 3/2*radius]]  
    Cavity_loc = [[3,0,0], [3, radius*math.sqrt(3), 0], [3, radius/2*math.sqrt(3), 3/2*radius]]  
    Initial_pos_vtk = [0, D1/2, D1/2]
    Initial_pos_stl = [0, D2/2, -D2/2]
    angles = [math.pi/6, -math.pi/6,0]
    res_pos = []
    res_pos2 = []
    vec_vtk=[]
    vec_vtk2=[]
    for i in range(3):
        temp = np.dot(Rx(angles[i]),Initial_pos_vtk)
        temp2 = np.dot(Rx(angles[i]),Initial_pos_stl)
        res_pos.append(np.asarray(temp).flatten())
        res_pos2.append(np.asarray(temp2).flatten())
        vec_vtk.append(  Actuator_loc[i] - res_pos[i])
        vec_vtk2.append(  Cavity_loc[i] - res_pos2[i]) 
    translations = [vec_vtk[0], vec_vtk[1], vec_vtk[2]]
    translations_cavity = [vec_vtk2[0], vec_vtk2[1], vec_vtk2[2]]
    translations_boxROI = Actuator_loc
    bottombox = [3,0.5*D1+(1/math.sqrt(2)+1)*radius,0.5*D1+(1/math.sqrt(2)+1)*radius,-10,-D1/2,-D1/2]  
     ## ============ variables for robot position =================##  
            
    for i in range(0,3):
        arm = self.addChild('arm' + str(i+1))
        arm.addObject('EulerImplicitSolver', name='odesolver', rayleighStiffness=0.1, rayleighMass=0.1)
        arm.addObject('SparseLDLSolver', name='preconditioner',template="CompressedRowSparseMatrixMat3x3d")
        arm.addObject('MeshVTKLoader', name='loader', filename=vtkMesh, translation=translations[i],rotation=[180/math.pi*angles[i],0,0] )
        arm.addObject('MeshTopology', src='@loader', name='container')
        arm.addObject('MechanicalObject', name='tetras', template='Vec3', showIndices=False, showIndicesScale=4e-5)
        arm.addObject('UniformMass', totalMass=0.20)
        arm.addObject('TetrahedronFEMForceField', template='Vec3', name='FEM', method='large', poissonRatio=0.3,
                        youngModulus=youngModulusStiffLayerFingers)
        arm.addObject('BoxROI', name='boxROI', box=bottombox, doUpdate=False,drawBoxes=True)
        if i == 0:
            arm.addObject('RestShapeSpringsForceField', points='@boxROI.indices', stiffness=1e12,
                            angularStiffness=1e12)
        else:
            arm.addObject('RestShapeSpringsForceField', points='@../finger1/boxROI.indices', stiffness=1e12,
                            angularStiffness=1e12)
        arm.addObject('LinearSolverConstraintCorrection')
        self.actuatedarms.append(arm)
        cavity = arm.addChild('cavity')
        cavity.addObject('MeshOBJLoader', name='cavityLoader', filename=OBJmesh_cavity, translation=translations_cavity[i], rotation=[angles[i] * 180 / math.pi, 0, 0])  
        cavity.addObject('MeshTopology', src='@cavityLoader', name='cavityTopo')
        cavity.addObject('MechanicalObject', name='cavity')
        cavity.addObject('SurfacePressureConstraint', name='SurfacePressureConstraint', template='Vec3', value=0.0001,
                         triangles='@topo.triangles', valueType='pressure')
        cavity.addObject('BarycentricMapping', name='mapping', mapForces=False, mapMasses=False)
        
        collisionModel = arm.addChild('collisionTube')
        collisionModel.addObject('MeshOBJLoader', name='cavityLoader', filename=OBJmesh_cavity, 
                                  translation=translations_cavity[i], rotation=[angles[i] * 180 / math.pi, 0, 0])
        collisionModel.addObject('MeshTopology', src='@cavityLoader', name='topo')
        collisionModel.addObject('MechanicalObject', name='collisMech')
        collisionModel.addObject('TriangleCollisionModel', selfCollision=False)
        collisionModel.addObject('LineCollisionModel', selfCollision=False)
        collisionModel.addObject('PointCollisionModel', selfCollision=False)
        collisionModel.addObject('BarycentricMapping')
        
        modelVisu = arm.addChild('visu')
        modelVisu.addObject('MeshSTLLoader', name='visualLoader', filename=STLmesh_shell)
        modelVisu.addObject('OglModel', name="visualModel",src=modelVisu.visualLoader.linkpath, color=[0.3, 0.7, 0.7, 0.7], translation=[0,0,0], rotation=[0,0,0])
        modelVisu.addObject('BarycentricMapping')
        
        
    self.addChild(UpperFrame())
    groupIndices,frames=_rigidify(self)
    print(frames)
    __attachToActuatedArms(self)


    return self

[hugtalbot]

Hi @ndolphin-github

There is several usual methods to attach objects in simulation such as :

• weak formulation using springs
• projective formulation
• Lagrange constraint resolution
  Here, the tutorial uses a mapping. Using mapping works considers that what is under the mapping belongs to the same object. So it is by design "attached".

Could you detail what you aim at modeling when saying "attach the rigid frame and three pneumatic actuators" ?
Is this your own robot model ?

[ndolphin-github]

Thanks for the reply @hugtalbot.
Yes it is the mesh model of our developed robot. The specific situation is there are three parallel linear actuators and all of them connected to the rigid frames just like a parallel manipulator. I am having an issue when connecting two different parts, elastic actuators and rigid frame in the SOFA simulation. I will try to follow the three options you recommended.

[hugtalbot]

I would need to have a better understanding of your actuators to advise properly @ndolphin-github
do you have some illustration?

FYI we are working on providing a robotic-dedicated GUI. We clearly notice that the SOFA semantic is not suiting roboticists' practices. A task force just started on this topic.

[ndolphin-github]

This is the simple version captured.

Three are pneumatic driven actuators and I am trying to attach rigid frame that connects all three of them as a one body.

[bakpaul]

Hi @ndolphin-github, did you manage to get the behavior you wanted following one of the three option @hugtalbot gave you ?

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