Rigid models flying apart when colliding

[Anonymous]

I have a scissors model that is made out of 4 parts, I can manipulate the full scissors to move with code, but as soon as it collides with another model it breaks apart into the four pieces. I tried to fix this behaviour by only allowing the keyboard keys to move the scissors, that fixed the breaking apart a bit but it stills breaks apart.

Before fix:

After fix:

So is there a way to treat the four parts as one rigid body in SOFA, and only be able to manipulate it using the keyboard.

Best,
Fayad

[Hugo]

Hi @fayad

In order to consider them all as Rigid parts, you can :

1. define one master Rigid node, with only one point
2. create subnodes for each Rigid part, and map them on the above single point with a RigidRigidMapping

Thus it would be considered as one rigid object.

Best

Hugo

[Anonymous]

Hi @Hugo

Thanks a lot, that worked, but now I am facing another problem with the rotation of individual parts, as I want to rotate the the tips, but I cannot since I have to rotate the master point to apply changes on the other parts, but it rotates everything which I dont want. In addition, after I collide with the prostate, the scissors start rotating and when I move the point it rotates instead of translating.

Sorry for the too many questions, thanks again

Best,
Fayad

[Hugo]

Hi @fayad

I needed to investigate myself, here is a solution using the ArticulatedSystemMapping.
Scene:

<?xml version="1.0" ?>
<Node name="root" dt="0.02" gravity="0 0 0">
        <RequiredPlugin name="SofaPython" pluginName="SofaPython" />
        <PythonScriptController filename="ChangeOrientation.py" classname="Rotate" listening="true"/>

        <EulerImplicit />
        <CGLinearSolver iterations="100" threshold="1e-6" tolerance="1e-6" />
        
        <MechanicalObject name="bati" template="Rigid" position="0 0 0   0 0 0 1"  />
        <UniformMass />

        <Node name="Grasper">
         
            <MechanicalObject name="Articulations" template="Vec1d" position="0 0" /> <!-- rest_position="0 0.52" -->
            <RestShapeSpringsForceField points="0 1" stiffness="100000    100000" printLog="true"/>

            <Node name="Jaws">
                <MechanicalObject name="GrasperDOFs" template="Rigid" position="0 0 0  0 0 0 1    0.1 0 0  0 0 0 1    0.2 0 0  0 0 0 1" showObject="1" showObjectScale="1"/>
                        
                <Node name="visualization">
                        
                    <Node name="handle_VM"> 
                        <OglModel name="VM" filename="mesh/dental_instrument.obj" color="red"  />
                        <RigidMapping  input="@../../GrasperDOFs" output="@VM" index="0" isMechanical="false" />
                    </Node>

                    <Node name="grasper-bottom_VM">
                        <OglModel name="VM" filename="mesh/dental_instrument.obj" rx="90" color="green"  />
                        <RigidMapping  input="@../../GrasperDOFs" output="@VM" index="1" />
                    </Node>
                    
                    <Node name="grasper-top_VM">
                        <OglModel name="VM" filename="mesh/dental_instrument.obj" ry="90" color="blue" /> 
                        <RigidMapping  input="@../../GrasperDOFs" output="@VM" index="2" />
                    </Node>
                                   
                </Node>
                               
                <ArticulatedSystemMapping input1="@../Articulations" output="@GrasperDOFs" input2="@../../bati"/>
            </Node>
            
            <ArticulatedHierarchyContainer/>
            <Node name="articulationCenters">
            
                <Node name="articulationCenter2">
                    <ArticulationCenter parentIndex="0" childIndex="1" posOnParent="0 0 -13" posOnChild="0 0 -13"/>
                    <Node name="articulations">
                        <Articulation translation="0" rotation="1" rotationAxis="0 1 0" articulationIndex="0"/>
                    </Node>
                </Node>

                <Node name="articulationCenter3">
                    <ArticulationCenter parentIndex="0" childIndex="2" posOnParent="0 0 -13" posOnChild="0 0 -13"/>
                    <Node name="articulations">
                        <Articulation translation="0" rotation="1" rotationAxis="0 -1 0" articulationIndex="1"/>
                    </Node>
                </Node>
            </Node>
        </Node>
</Node>

with a python script:

import sys
import Sofa

class Rotate(Sofa.PythonScriptController):
    def initGraph(self,node):
        self.Articulations=node.getChild('Grasper').getObject('Articulations')
        return 0
        
    def onKeyPressed(self,k):
        
        if k=="M" :
            rotation = self.Articulations.findData('position').value
            rotation[1][0] = rotation[1][0] - 0.1
            self.Articulations.findData('position').value = rotation
            self.Articulations.findData('rest_position').value = rotation
            print ' M '

        if k=="L" :
            rotation = self.Articulations.findData('position').value
            rotation[1][0] = rotation[1][0] + 0.1
            self.Articulations.findData('position').value = rotation
            self.Articulations.findData('rest_position').value = rotation            
            print ' L '
        return 0

Do not hesitate to post us your resulting video 😉
Best wishes,

Hugo

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