Rope Pincer Grip

Discussion in 'Support requests' started by jolkin, Mar 13, 2019.

  1. I am currently attempting to pick up a rope using a pincer grip. However, every time I attempt to lift the rope, it slips through my gripper, regardless of the amount of force I apply (I’ve tried this with up to 100N). I have followed other forum posts where it was advised that people change the solref and solimp values, and I’ve also made sure that I’m using an elliptical solver instead of the pyramidal one.

    My question is two-fold: is there a way for me to consistently pick up a composite rope object with a pincer grip? And if not, is there a way for me to circumvent this by manually setting the position of the rope?

    I’ve attached the model files for both the gripper as well as the rope.


    Attached Files:

  2. Emo Todorov

    Emo Todorov Administrator Staff Member

    Sorry about the delay. Your files have missing dependencies (includes) so I could not load them. In general, composite objects are made of spheres or other primitives, and there is some spacing between them. So you have to make sure the gripper does not pass through that space -- by making the gripper larger, or the spacing smaller.

    If you have enough contact points but the grasp is still unstable, you can try the elliptic contact model with impratio set to say 5. Or you can enable the noslip solver (but try the first option first). Both of these reduce slip.

    Also, it helps to use torsional friction for grasping (by setting condim=4). Soft fingerpads make distributed contacts with objects, and effectively have torsional friction. MuJoCo does not explicitly model the contact area, but allows you to include torsional friction directly which has a similar stabilizing effect.