Lattice-based Robots Hardware

Modules are constrained to occupy positions in a virtual grid, or lattice in lattice-based systems. One of the simplest module shapes in a 2D lattice based system is a square, but more complex polygons such as a hexagon (and a rhombic dodecahedron in 3D) have also been proposed. Because of the discrete, regular nature of their structure, developing algorithms for lattice-based systems is often easier than for other systems. The grid constraint makes implementing certain rolling motions, such as the tank-tread, more challenging since module attachment and detachment is required. We would like to develop algorithms implementable by most, or all, lattice-based systems, so a complete review of their properties is essential.

One of the first lattice-based SR robots planned and constructed in hardware is the Fracta robot. The 2D Fractum modules link to each other using electromagnets. Communication is achieved through infrared devices embedded in the sides of the units, and allows one fractum to communicate with its neighbors. Computation is also onboard; each fractum contains an 8-bit microprocessor. Power, however, is provided either through tethers or from electrical contacts with the base plane.

This system was designed for self-assembly, and can form simple symmetric shapes such as a triangle, as well as arbitrary shapes. Other lattice-based robots include a smaller 2D system, and a 3D system. Another early SR robot is the Metamorphic Robot. The basic unit of this robot is a six-bar linkage forming a hexagon. The kinematics of this shape was investigated when the design was proposed, and hardware prototypes were constructed later. A unique characteristic of this system is that it can directly implement a convex transition; a given module can move around its neighbor with no supporting structure.

The hexagon deforms and translates in an owing motion. A square shape with this same property was also proposed. This motion primitive is important since it is required by many general reconfiguration algorithms, but many systems can only implement it using a group of basic units working together.