How much gas does it take to fill a bladder in vacuum to a malleable shape not at the limits of maximum inflation shape while in a relaxed condition (not under tension)?
Originally Posted by IsaacKuo
Are you saying that the object (being gripped) exerts a negative pressure, pulling the bladder membrane against itself?
Sure, this means that there is no air pressure on the concave portion of the gripper to keep it pressed up against the coffee grinds. So what? The object itself
provides the pressure to keep it pressed up against the coffee grinds. And that, ultimately is the point. In any case, there needs to be some excess force pressing the gripper surface against the object, or it can't grip.
In the Gripper in the video, ambient air pressure doesn't force the gripper onto the object, it forces the granular material inward against itself from all directions and that friction allows it to lock into a position. This is why coffee grounds in vacuum-pack bricks are so hard (the plastic-foil package is not using elasticity). And I think the thick bladder material's sticky and springy properties allows it to exert force against the object to maintain friction on it (with the packed and locked coffee grains not allowing it to loosen up). Even if gas pressure wasn't used, the act of pulling on the bladder would not pull inward but backward and away from the object surface, causing the part of the bladder that wrapped around something to peel back.
It's the same mechanism that explains why a rubber surgical glove turns inside-out when pulled off. Now, it might be possible to use granular material to make the pull back stop and pull on what's inside it, but that's because it has a preformed concave cylindrical cavities used on conforming cylindrical shapes, which would be lacking on a spheroidal bladder meant for grabbing onto any shape.
Et tu BAUT? Quantum mutatus ab illo.