Strange dynamics with composite object

Discussion in 'Modeling' started by Xingyu Lin, Dec 11, 2018.

  1. Hi,

    I used the new composite feature and built a rope environment. However, the dynamic seems a bit strange: When a robot gripper touches the rope with a relative medium velocity, the gripper goes through the rope. A video of such behavior is attached. I wonder if there is something wrong with my modeling of either the robot or the rope? The rope and the gripper are in the same collision group and when the speed of the gripper is very slow, this does not happen.

    The XML file for the rope or the robot can be viewed here:


    Attached Files:

    Last edited: Dec 11, 2018
  2. Emo Todorov

    Emo Todorov Administrator Staff Member

    This should not be happening. It may help to turn on the visualization of contact points and contact forces and see what contacts are detected when. If you can step the simulation frame by frame it will be easier to see it. It is possible that the maximum numbers of contacts and constraints in your model are too small, in which case the simulator will automatically discard contacts/constraints that do not fit in the buffer, and raise a warning.

    If you are getting contact interactions at small velocities but not at large velocities, it could be that your contacts are too soft.
  3. Thank you for the reply! The number of maximum constraints is properly set so that there aren't any warnings for the discarded contacts/constraints. I do not quite understand where to tune the 'softness' of the constraint? What attributes of the rope or the gripper need to be set?
  4. Emo Todorov

    Emo Todorov Administrator Staff Member

    Constraint parameters and softness are described in the online documentation.
  5. I am having a similar problem. In my case, I'm trying to grasp a deformable object (which is very similar to the example given in documentation).
    The behavior can be seen in the attached video.

    Attached Files:

  6. Did you fix it at @Tarik ?