Imagine that you have a big box of sand in which you bury a tiny model of a footstool. A few seconds later, you reach into the box and pull out a full-size footstool: The sand has assembled itself into a large-scale replica of the model.
Unlike many other approaches to reconfigurable robots, smart sand uses a subtractive method, akin to stone carving, rather than an additive method, akin to snapping LEGO blocks together. A heap of smart sand would be analogous to the rough block of stone that a sculptor begins with. The individual grains would pass messages back and forth and selectively attach to each other to form a three-dimensional object; the grains not necessary to build that object would simply fall away. When the object had served its purpose, it would be returned to the heap. Its constituent grains would detach from each other, becoming free to participate in the formation of a new shape.
Each programmable matter pebble is a 12mm per side, and together they
are able to form complex 2D shapes using four electropermanent magnets
able to hold over 80 times the individual module weight. The pebbles are
formed by wrapping a flexible circuit around a brass frame. An energy
storage capacitor hangs between two tabs occupies the center of the
To form shapes through subtraction, modules initially self-assemble into
a close-packed block of material (a). Once this initial structure is
complete, and all modules are fully latched to their neighbors (b), the
modules not needed in the final structure detach from the neighbors (c).
Once, these extra modules are removed, we are left with the final shape