Make composite object less soft

Discussion in 'Modeling' started by Martin Hwasser, Sep 16, 2019.

  1. I am trying to model a deformable object, think a paper box, like a package of cereals. I've attached an XML file to show how a heavy object deforms it when it is placed on top. But how would I make the composite box less deformable?
     

    Attached Files:

    • box.xml
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  2. I have a very similar problem. I'm trying to grasp a soft object (composite/box) with a robotic gripper. Each experiment is performed with the same gripping force.
    As I understood from the documentation the effect of softness should be easily modelled by setting stiffness and damping parameters in composite/tendon and composite/joint elements. Unfortunately, I can't see any difference in object behaviour while being grasped between the high values of these parameters and low.
     
  3. OK, I think I figured it out.
    According to http://www.mujoco.org/book/modeling.html#CSolver when the solref parameter is set to negative numbers, the new format is introduced, which is (-stiffness, -damping). It allows us to make a soft element less soft by using a stiffness parameter. See the below code.

    Code:
        <!--SPONGE-->
        <worldbody>
            <body pos="1.4 -0.02 0.8">
                <freejoint/>
                <composite type="box" count="7 7 7" spacing="0.27">
                    <geom type="capsule" size=".15 0.2" rgba=".8 .2 .1 1" mass="0.003" contype="0" conaffinity="1"/>
                    <joint kind="main" stiffness="1 " damping="1" solreffix="-0.05 -1"/>
                    <tendon kind="main" stiffness="1"  damping="1" solreffix="-0.05 -1"/>
                </composite>
            </body>
        </worldbody>