Trouble with a closed Kinematic loop

Discussion in 'Modeling' started by Adam Allevato, Mar 9, 2018.

  1. I'm attempting to model the Robotiq 2-finger adaptive gripper. Each finger is an underactuated 2-DOF, fivebar mechanism, but I'm modeling it with the underactuated joint pinned, which turns each finger into a 1-DOF fourbar.

    I'm currently trying to use an "connect" equality constraint to connect the outer joint of the finger to the fingertip (closing the kinematic loop), but once I do this, the mechanism is unable to move, even with all joints being unlimited (just to be safe). I also disabled collisions between all the geoms by setting their contype to 2 in case that was causing issues.

    This is a simple fourbar that is not at a toggle point, so I'm not sure what the issue could be. I looked in some of the downloadable resources for guidance, but didn't see any that included a kinematic loop. I've attached a minimal working example.
     

    Attached Files:

    wutter likes this.
  2. Emo Todorov

    Emo Todorov Administrator Staff Member

    Looks like you connected the bodies at the wrong place. The red sphere in the image shows your anchor point.

    There is a model of this robot in the Resources now.


    upload_2018-5-19_23-38-36.png
     
  3. Where is it? I see a model of the 3-finger gripper but not the 2-finger one with the closed kinematic loop.
     
    wutter likes this.
  4. Also looking for help with this particular gripper. @Gautam Salhotra, were you able to figure it out?