I'm trying to implement a magnetic/suction-type grasping, where I want the object to stick to the gripper and move along with it in a rigid manner. I found this thread, where using weld equality is recommended. When I tried implementing it, the behavior is reasonable when the robot gripper moves up/down, but it's odd when the gripper is rotated (see attached video). I've added 2 weld constraints -- one attaching the object to the left fingertip, and the other to the right fingertip. The solver parameters are solimp="0.9 0.95 0.001" and solref="0.004 50000". I also tried a single weld constraint with object attached to the gripper base, but I'm seeing a similar behavior.