Constructing models

Constructing rigid body models

Setting up mass and inertial properties

• To set from primitives in XML use InertiaFromPrimitive:

<RigidBody id="box" enabled="true" position="0 .5000 0" angular-velocity="0 10.00 0" visualization-id="b1" linear-velocity="0 0 0">
  <InertiaFromPrimitive primitive-id="b1" />
</RigidBody>

• To do this in code, set the mass of your primitive, then use set_inertia, passing the inertia of your primitive

  Moby::PrimitivePtr box_prim(new Moby::BoxPrimitive(1, 1, 1));
  box_prim->set_mass(10);

  Moby::RigidBodyPtr box(new Moby::RigidBody());
  box->set_inertia(box_prim->get_inertia());

Setting up geometries for collision

• Set geometries for collision from a primitive with CollisionGeometry

<RigidBody id="box" enabled="true" position="0 .5000 0" angular-velocity="0 10.00 0" visualization-id="b1" linear-velocity="0 0 0">
  <InertiaFromPrimitive primitive-id="b1" />
  <CollisionGeometry primitive-id="b1" />
</RigidBody>

• Do this in code with a CollisionGeometry object, taking the geometry from a primitive

  Moby::CollisionGeometryPtr box1CG(new Moby::CollisionGeometry());
  box1CG->set_single_body(box);   //box is the RigidBody
  box1CG->set_geometry(box_prim1);

Setting up geometries for visualization

• Can do this from primitives using visualization-id

<RigidBody id="box" enabled="true" position="0 .5000 0" angular-velocity="0 10.00 0" visualization-id="b1" linear-velocity="0 0 0">
</RigidBody>

• If you wish to use a more sophisticated geometry than what comes from a primitive, specify that with vvisualization-filename

<RigidBody name="ground" id="ground" enabled="false" vvisualization-filename="ground.wrl" position="0 -.25 0">
</RigidBody>

• You can also do this in code from primitives

  Moby::PrimitivePtr box_prim1(new Moby::BoxPrimitive(1, 1, 1));
  
  Moby::RigidBodyPtr box(new Moby::RigidBody());
  box->set_visualization_data(box_prim1->create_visualization());

Constructing articulated body models

• Example syntax for an articulated body model

<RCArticulatedBody id="FEEDER" floating-base="false" fdyn-algorithm="crb"
      fdyn-algorithm-frame="link" rotate="0.0 0.05 0.0" translate="0.45,0,0" >
</RCArticulatedBody>

• The floating-base parameter indicates whether the base is affixed to the environment or "floating"
• Setup each link like a rigid body

<RCArticulatedBody id="FEEDER" floating-base="false" fdyn-algorithm="crb"
   fdyn-algorithm-frame="link" rotate="0.0 0.05 0.0" translate="0.45,0,0" >
  <RigidBody id="BASE" color="0 0 0 0" position="0 0 -0.02" angular-velocity="0 0 0" linear-velocity="0 0 0" visualization-id="base" compliant="false">
  </RigidBody>

  <!-- the body -->
  <RigidBody id="SLIDE1" color="0 0 0 0" position="0 0 0" angular-velocity="0 0 0" linear-velocity="0 0 0" visualization-id="slide1-viz" compliant="false">
    <CollisionGeometry primitive-id="slide1" />
    <InertiaFromPrimitive primitive-id="slide1-viz" />
  </RigidBody>
  
  <RigidBody id="SLIDE2" color="0 0.5 0 1" position="0 0.055 0.01" angular-velocity="0 0 0" linear-velocity="0 0 0" visualization-id="slide2-viz" compliant="false">
    <CollisionGeometry primitive-id="slide2" />
    <InertiaFromPrimitive primitive-id="slide2-viz" />
  </RigidBody>
  <!-- ...full example in Moby/example/parts-feeder/feeder.xml... -->
</RCArticulatedBody>

• Setup body kinematics (set where each joint is located and its axis/axes)

<RCArticulatedBody id="FEEDER" floating-base="false" fdyn-algorithm="crb"
   fdyn-algorithm-frame="link" rotate="0.0 0.05 0.0" translate="0.45,0,0" >
  <RigidBody id="BASE" color="0 0 0 0" position="0 0 -0.02" angular-velocity="0 0 0" linear-velocity="0 0 0" visualization-id="base" compliant="false">
  </RigidBody>

  <PrismaticJoint id="shaker" location="0 0 0" inboard-link-id="BASE" outboard-link-id="SLIDE1" axis="1 0 0"/>

  <!-- the body -->
  <RigidBody id="SLIDE1" color="0 0 0 0" position="0 0 0" angular-velocity="0 0 0" linear-velocity="0 0 0" visualization-id="slide1-viz" compliant="false">
    <CollisionGeometry primitive-id="slide1" />
    <InertiaFromPrimitive primitive-id="slide1-viz" />
  </RigidBody>
  
  <FixedJoint id="fj1" location="0 0 0" inboard-link-id="SLIDE1" outboard-link-id="SLIDE2" />

  <RigidBody id="SLIDE2" color="0 0.5 0 1" position="0 0.055 0.01" angular-velocity="0 0 0" linear-velocity="0 0 0" visualization-id="slide2-viz" compliant="false">
    <CollisionGeometry primitive-id="slide2" />
    <InertiaFromPrimitive primitive-id="slide2-viz" />
  </RigidBody>
  <!-- ...full example in Moby/example/parts-feeder/feeder.xml... -->
</RCArticulatedBody>

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