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?
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.
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>