Robot metabolism: Toward machines that can grow by consuming other machines

Abstract

Biological lifeforms can heal, grow, adapt, and reproduce, which are abilities essential for sustained survival and development. In contrast, robots today are primarily monolithic machines with limited ability to self-repair, physically develop, or incorporate material from their environments. While robot minds rapidly evolve new behaviors through artificial intelligence, their bodies remain closed systems, unable to systematically integrate material to grow or heal. We argue that open-ended physical adaptation is only possible when robots are designed using a small repertoire of simple modules. This allows machines to mechanically adapt by consuming parts from other machines or their surroundings and shed broken components. We demonstrate this principle on a truss modular robot platform. We show how robots can grow bigger, faster, and more capable by consuming materials from their environment and other robots. We suggest that machine metabolic processes like those demonstrated here will be an essential part of any sustained future robot ecology.

Fig. 1.. Robot metabolism allows machines to “grow.”

Robot modules can grow by consuming and reusing parts from their environment and other robots. This ability, essential to biological lifeforms, is crucial for developing a self-sustaining robot ecology. This paper demonstrates the above developmental sequence in detail: from individual modules to a fully assembled ratchet tetrahedron robot.

Fig. 2.. Truss Links can expand and contract, attach and detach, and connect to multiple other Truss Links at once.

(A) A contracted Truss Link is 28 cm long and weighs 280 g (B). When fully expanded, a Truss Link can increase its length by over 53% to 43 cm. Images (C and D) show the interior of the magnet connector in an active state with the magnet exposed at the tip and a fully-contracted, i.e., nonactive state with the magnet retracted, respectively. The conical compression spring inside the connector resets the magnet connector to the active state after retracting it, so the Truss Link is ready to connect again. The spherical neodymium magnet is held in position by a magnet holder. The magnet holder allows the magnet to rotate freely to rotate to an equilibrium position when approached by another magnet. This mechanism ensures a strong connection between multiple links from a wide and continuous range of angles. We show connections between (E) two, (F) three, and (G) four connectors.

Fig. 3.. Truss Links can develop 3D structures by absorbing and integrating material.

(A) shows a series of topological transitions, starting on the left from a group of individual links and ending on the right with a ratchet-tetrahedron topology. Starting from six independent links, three links combine to form a three-pointed star shape, and the other three combine to form a triangle. Next, the triangle absorbs the three-pointed star by connecting to it and becomes a diamond-with-tail topology. The diamond-with-tail then folds itself into a tetrahedron. Next, the tetrahedron finds and integrates a free Truss Link by connecting and picking it up from the ground to form a ratchet tetrahedron. (B) shows the profile view of the experiment environment (not to scale), clarifying where each transition shown in (C) to (E) took place with section labels (B-a) through (B-d) as a reference. The frame sequences in (C), (D), and (E) show the formation of a diamond-with-tail, a tetrahedron robot, and a ratchet tetrahedron, respectively.

Fig. 4.. Ratchet tetrahedron robots gain speed at the cost of consistency.

The graph visualizes the locomotion speeds of a single Truss Link, a triangle, a tetrahedron, and a ratchet tetrahedron. The error bars show the SD from the mean. The experiment was conducted on a flat, carpeted, 10° decline.

Fig. 5.. Simulated random topology formation probabilities over 2000 20-min simulation runs.

Fig. 6.. A Truss Link triangle robot recovers its shape after impact.

A Truss Link triangle robot crawls off a ledge, breaks a connection due to the impact, proceeds to recover its triangle shape, and crawls away.

Fig. 7.. A Truss Link–based three-pointed star and diamond-with-tail robot recover their original form after breaking connections due to impact.

(A) A three-pointed star robot crawls off a ledge and breaks all Truss Link connections. The robot then regains a three-pointed star shape and crawls away. (B) A Truss Link diamond-with-tail robot crawls off a ledge and separates into a three-pointed star and a triangle robot. The three-pointed star robot lands on top of the triangle robot. Next, the three-pointed star robot crawls off the triangle and reconnects to it, ultimately regaining the diamond-with-tail shape.

Fig. 8.. A ratchet-tetrahedron sheds a “dead” ratchet Truss Link and picks up a replacement.

The ratchet tetrahedron approaches the single Truss Link and latches onto it. Next, it sheds the dead link: The fully contracted and detached “dead” Truss Link falls off of the tetrahedron and rolls down the slope. The tetrahedron then topples itself twice to re-orient itself to pick up the newly found Truss Link. After the pickup at t = 192 s, the tetrahedron swings the Truss Link into its center and ratchets away.

Fig. 9.. A ratchet tetrahedron raises a 2D robot to become a tetrahedron robot.

A ratchet tetrahedron uses its ratchet Truss Link to fish through a hole in the white platform for the vertex where the triangle and the three-pointed star are connected. After being lifted up, the three-pointed star connects to the two free vertices of the triangle, forming the tetrahedron. The different, time-synchronized camera angles in the frame sequence were picked based on which camera provided the most informative view of each stage.