Here is a slightly-modified version of FuzzyCow's Lego "DualGrabber" design ( www.mocpages.com/moc.php/397424 ). It is a one-motor grab-then-lift design. The topmost Lego Technic Gear contacts a gear on the main Lego robot that you design. If you spin that gear, the jaws of the grabber close upon an object, then lift the object upwards -- all with one motor! To reduce the crushing force, one could substitute that white #60c01 "Technic, Gear 24 Tooth Clutch" ( www.bricklink.com/catalogItem.asp?P=60c01 ) that is shown in front of the robot for the 24-Tooth Technic Gear. That way, the internal clutch will slip when the jaws are fully closed onto the object being lifted. The various #45590 "Technic, Axle Connector Double Flexible (Rubber)" pieces ( www.bricklink.com/catalogItem.asp?P=45590 ) can be moved around and adjusted to best grasp the object.
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