Update Solid and Shell plugins to use FlexComp.

PiperOrigin-RevId: 573755821
Change-Id: I3b8d7fb27f0e940038fa9fd2b26ecc746df4f7ac

model/plugin/elasticity/floppy_flex.xml

@@ -0,0 +1,54 @@
+<!-- Copyright 2021 DeepMind Technologies Limited
+
+     Licensed under the Apache License, Version 2.0 (the "License");
+     you may not use this file except in compliance with the License.
+     You may obtain a copy of the License at
+
+         http://www.apache.org/licenses/LICENSE-2.0
+
+     Unless required by applicable law or agreed to in writing, software
+     distributed under the License is distributed on an "AS IS" BASIS,
+     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+     See the License for the specific language governing permissions and
+     limitations under the License.
+-->
+
+<mujoco model="Floppy">
+  <include file="scene.xml"/>
+
+  <extension>
+    <plugin plugin="mujoco.elasticity.solid"/>
+  </extension>
+
+  <compiler autolimits="true"/>
+
+  <option solver="CG" tolerance="1e-6" timestep=".001" integrator="implicitfast"/>
+
+  <size memory="100M"/>
+
+  <visual>
+    <map stiffness="100"/>
+  </visual>
+
+  <worldbody>
+    <flexcomp type="grid" count="24 4 4" spacing=".1 .1 .1" pos=".1 0 1.5"
+              radius=".0" rgba="0 .7 .7 1" name="softbody" dim="3" mass="7">
+      <contact condim="3" solref="0.01 1" solimp=".95 .99 .0001" selfcollide="none"/>
+      <edge damping="1"/>
+      <plugin plugin="mujoco.elasticity.solid">
+        <config key="poisson" value="0.2"/>
+        <!--Units are in Pa (SI)-->
+        <config key="young" value="5e4"/>
+      </plugin>
+    </flexcomp>
+
+    <body>
+      <joint name="hinge" pos="0 0 .5" axis="0 1 0" damping="50"/>
+      <geom type="cylinder" size=".4" fromto="0 -.5 .5 0 .5 .5" density="300"/>
+    </body>
+  </worldbody>
+
+  <actuator>
+    <motor name="cylinder" joint="hinge" gear="1 0 0 0 0 0" ctrlrange="-100 100"/>
+  </actuator>
+</mujoco>