[SOLVED] How to set a FixedTranslationConstraint on a specific mesh index?

[Noura]

Hello,

I’m trying to figure out how it is possible to impose a FixedTranslationConstraint on a specific point in a rigid model.

Here is a minimal simulation scene which demonstrates the wrong behavior: A torque is applied, the constraint is set on wrong position (the center of mass), and I added a text label “fixation” at the desired fixation position.

You need to download the required .obj file here.

I would appreciate the motivated person to look into my scene during the hottest summer days 😉

Noura

<?xml version="1.0"?>

<Node name="root" gravity="0 0 0" dt="0.01"  >
    <EulerImplicitSolver rayleighStiffness="0.01"/>
    <CGLinearSolver iterations="50" tolerance="1e-06" threshold="1e-06"/>
    <VisualStyle name="visualStyle" displayFlags=" showWireframe showBehavior" />  
    <BruteForceDetection name="bruteForceDetection1" />
    <DefaultContactManager name="defaultContactManager1"  response="default" />
    <DefaultPipeline name="defaultPipeline1" />
    <MinProximityIntersection name="minProximityIntersection1"  alarmDistance="0.2"  contactDistance="0.1" />

<Node name="Radius" activated="1" >

    <MechanicalObject name="MO_Radius" template="Rigid3d" position="-15.6818 124.415 -260.548 0 0 0 1" />
	<UniformMass totalmass="10"/>
	
<!-- Right now, I'm setting the FixedTranslationConstraint here on the centre of mass, but it is not the position where I would like to -->
    <FixedTranslationConstraint template="Rigid3d"/>
        
<!--    Supnation -->
    <TorsionForceField indices="0" torque="-20" axis="0.02	0.024	0.96" origin="-27.39  121.61  -368.12"/>

<!--    Pronation    -->
<!--     <TorsionForceField indices="0" torque="20" axis="0.02	0.024	0.96" origin="-27.39  121.61  -368.12"/> -->

	<Node name="Visual_Radius" activated="1" >
		<OglModel name="VisualModel" filename="Radius.obj" color="0 0 1" />
		<RigidMapping input="@../MO_Radius" output="@VisualModel" />
	</Node>
    
	<Node name="Surface_Radius" activated="1" >
		<MeshObjLoader name="loader" filename="Radius.obj" />
		<Mesh src="@loader" />
		<MechanicalObject name="MO" src="@loader" />
<!--         Can't set a FixedTranslationConstraint on a specific point defined by its index (1011 is the index of the point RAF_Proximal introduced later in the scene-->
<!--         <FixedTranslationConstraint name="fixation_poisition" indices="1011" />   -->  
        <RigidMapping input="@../MO_Radius" output="@MO"/>
		<Triangle/>
		<Line />
		<Point/>
		
	</Node>
</Node>

<!-- Visualization of the rotation axis and two points of interest -->
<Node name="Rotation_axis_Visu" activated="1">
    <OglModel   template="ExtVec3f"
                position="-27.39 120.38 -367.86 -0.038 152.33 -171.65 "  edges="1 0 "
                material="Default Diffuse 0 0 1 0 1 Ambient 1 1 1 0 1 Specular 0 0.333333 0 1 0 Emissive 0 0 1 0 1 Shininess 0 45"
                lineWidth="7"  primitiveType="DEFAULT"  blendEquation="GL_FUNC_ADD"  sfactor="GL_SRC_ALPHA"  dfactor="GL_ONE_MINUS_SRC_ALPHA"/>
</Node>

<!-- The bone should be fixed against translations at this position -->
<Node name="RAF_Proximal" activated="1">
	<Visual3DText text="Fixation" position="-27.396 120.38 -375" scale="1" />
    <MechanicalObject name="p1_radius" template="Rigid3d" dx="-27.396" dy="120.38" dz="-367.86" rx="0" ry="0" rz="0" />           
    <UniformMass totalmass="1" />
    
</Node>

<Node name="RAF_Distal" activated="1">
    <MechanicalObject name="p2_ulna" template="Rigid3d" dx="-0.038966" dy="152.33" dz="-171.65" rx="0" ry="0" rz="0" />           
    <UniformMass totalmass="1" />
</Node>

</Node>

[Binesh]

Hi @Noura
in your scene , you loaded a mesh with mesh loader and mapped it to one point and apply fixedConstraint to MO_Radius mechanical object . so your fixedConstraint work with MO_Radius mechanical object and fix 1 point .

you can use fixed constraint in your mesh topolgy node and give it a correct index

Or

you can use “PartialFixedConstraint” instead of “FixedTranslationConstraint”

[Noura]

Hi @Binesh,

Thanks for your comment.
In my current scene, there is no mesh topology node. Do you mean in the “Surface_Radius” Node? If yes, I already tried to set both: once a “FixedConstraint” and then a “PartialFixedConstraint” on the vertex (which has index no 1011). None of these lines:
<FixedConstraint name="fixation_poisition" indices="1011" />
<PartialFixedConstraint name="fixation_poisition" indices="1011" />

has an influence, and the point is still moving!

Even if one of both solution would work (which means restricting the motion of the vertex), I think that it is not the appropriate way because this would constraint the rotation as well which is not what should happen.

Any other suggestions?

Noura

[Hugo]

Hi @noura

I am not sure to understand what you want to simulate.
You apply a rotation on the center of mass, the object rotates indeed.

But what is the constraint you want to apply?

[Noura]

Hi Hugo,

No matter where the torque is applied (on the center of mass or on another point), the proximal extremity of the bone (Node RAF_Proximal in the scene) should be fixed against translation.
In other words, imagine that the bone is mounted to a fixation device at this point (RAF_Proximal) which allows it only to rotate but not to go away.

Hope that it is clear now?

Noura

[Binesh]

@Noura
your bone can rotate only
Is this not true?
I checked your scene very much and look like every thing is OK
I do not know exactly what the problem is 😀

[Noura]

Thanks @Hugo and @Binesh for your attempts!

We managed finally to fix our simulation.
Solution was by replacing the MechanicalObject position by a different one (the base of the bone instead of its center of mass), and it works as desired.

Best,

Noura

[Hugo]

Great to hear!
Thanks for the feedback Noura !!

[Author]

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