Friction between gripper and stone not working properly

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Hi there,

I'm using Gazebo to simulate a pick and place of objects with irregular shape like meshes of stones. When picking an object Gazebo does not seem to take the friction between both objects (stone and gripper ) into account.

Here is a quick video of what happens: https://www.dropbox.com/s/8svnza7dze0...

The friction coefficients of both objects are:

Stone

<gazebo reference="base_link">
  <mu1 value="1.2"/>
  <mu2 value="1.1"/>
  <kp  value="5000000.0" />
  <kd  value="1.0" />
  <fdir1 value="1 0 0"/>
  <collision>
    <surface>
      <bounce>
        <restitution_coefficient> 0.1 </restitution_coefficient>
        <threshold>0.</threshold>
      </bounce>
      <contact>
        <ode>
          <max_vel>0.1</max_vel>
          <min_depth>0.001</min_depth>
        </ode>
      </contact>
    </surface>
  </collision>
  <material name="Gray">
    <color rgba="0.8 0.8 0.8 1"/>
  </material>
  <turnGravityOff>false</turnGravityOff>
</gazebo>

and

Gripper

<!-- Link 3 -->
<link name="${prefix}link_3">
  <visual>
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <geometry>
      <mesh filename="package://robotiq_s_model_visualization/meshes/s-model_articulated/visual/link_3.STL" />
    </geometry>
    <material name="grey"/>
  </visual>
  <collision>
    <origin xyz="0 0 0" rpy="0 0 0"/>
    <geometry>
      <mesh filename="package://robotiq_s_model_visualization/meshes/s-model_articulated/collision/link_3.STL"/>
    </geometry>
    <material name="grey"/>
  </collision>
  <inertial>
    <origin rpy="0 0 0" xyz="0.01626 0.00049 0.0002"/>
    <mass value="0.03354"/>
    <inertia ixx="0.00000305151"
             ixy="0.00000089792"
             ixz="0.00000000249"
             iyy="0.00001427978"
             iyz="-0.00000001191"
             izz="0.00001264126"/>
  </inertial>
</link>

<gazebo reference="${prefix}link_3">
  <mu1>1.1</mu1>
  <mu2>1.1</mu2>
  <minDepth>0.001</minDepth>
</gazebo>

Link_3 is the finger tip of the gripper as seen in the video above.