UR5 robot breaks after small collision

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Hi,

I am working with the simulated UR5 with a gripper, and I am trying to simulate the collision between the gripper and some object (for now just a wooden box). The problem is that whenever the robot collides with the box it wildly bounce off and most of the time if the collision is slightly strong then the controller breaks.

You can see it here https://youtu.be/aab2w8Ymc7o

I am using the following collision parameters for the wooden box :

    <collision name="collision">
    ...
    <surface>
      <contact>
        <poissons_ratio>0.347</poissons_ratio>
        <elastic_modulus>8.8e+09</elastic_modulus>
        <ode>
          <soft_cfm>0.2</soft_cfm>
          <soft_erp>0.2</soft_erp>
          <kp>1000</kp>
          <kd>10</kd>
          <max_vel>100.0</max_vel>
          <min_depth>0.001</min_depth>
        </ode>
      </contact>
    </surface>

In the case of the robot joints, I define small damping like:

<joint name=...>
  ...
  <dynamics damping="0.7" friction="0.0"/>
</joint>

How can I get a more realistic interaction between the robot and the object? I want the robot to behave stiffer instead of bouncing like crazy at any small collision.

I am using gazebo 7.14.0 with ROS Kinetic in Ubuntu 16.04.

Thanks!