The basic shape of each robot is roughly a hexagon surface between 2 and 3 feet in diameter, with a large rim to allow for a solid yet flexible interconnect. A single drive wheel with the capacity for high maneuverability should propel these around.
The shape of these would not be a perfect hexagon. By changing the line of each edge of the hex to an S shape, we can create a figure that is attractive and facilitates alignment of the hexes. We've discussed using light in the resultant tongue and groove interlock for identification. We can run a light pipe along the top edge to illuminate and define the line.
More discussion can be found on Tessellations