The constructions can either lift, roll, jump or throw: Researchers have developed “muscular” hexagonal components that can be linked together to form versatile robots based on the LEGO principle. The units can be mechanically and electrically linked to one another using magnets on their exoskeleton. The so-called HEXEL modules are powered by a system of electro-hydraulic “artificial muscles” inspired by nature. The concept allows particularly light robots to be configured with different capabilities that could be used in space or rescue missions, say the developers.
As is well known, sophisticated robotic systems can already relieve people of certain tasks or carry out specific tasks. For some applications, however, more versatile concepts would be desirable – robots that can spontaneously adapt to new challenges and tasks. One promising approach is systems built from modules that can be quickly reconfigured to create new configurations. Such concepts have already been developed, but there is still a need for optimization. The developments to date are usually complicated and, due to the use of DC motors, relatively heavy and energy-hungry.
Muscular hexagonal units
The new system, which researchers from the Max Planck Institute for Intelligent Systems in Stuttgart (MPI-IS) are now presenting, is comparatively “slim”. It is based on modules made of six light glass fiber plates that are connected to one another via flexible joints. Instead of motors, electrohydraulic bags are attached to them, which move the rigid elements – similar to how muscles move bones in animals. By applying voltage to the module, the differently polarized walls in the upper part of the artificial muscle bags contract due to electrostatic attraction. This then shifts fluid, causing the artificial muscles to shorten.
Video: A HEXEL module jumps high into the air. © Darrell J. Irvine
In the so-called HEXEL modules, this leads to a bending of the joints between the glass fiber plates, so that they change their shape from long and narrow to wide and flat. As the researchers demonstrate, the electrostatic initial and final voltage enables the HEXEL modules to change shape very quickly. The movement is so sudden that they can jump up to four times their own size. The developers show that the effect can also be used to make a ball fly into the air.
Design options based on the LEGO principle
However, the HEXELs become particularly powerful and versatile when they are linked to form complex units. This is made possible by magnets that the team has integrated into the six glass fiber plates of each module. The force of attraction allows these to be assembled into different formations using the LEGO building block principle. They can also be electrically coupled so that the activation voltage can be transmitted to specific functional units. “By connecting several modules together, we can create new robot geometries and reuse them for different requirements,” says co-first author Ellen Rumley from the MPI-IS.
The researchers have already demonstrated the wide range of possible applications in the study with a number of examples. They show, for example, how HEXELs can be combined to create a combined force that enables weights to be lifted. By partially activating certain parts of a structure, attached components can also be deflected. In addition, HEXEL structures that are moved rhythmically in a special way can crawl through narrow spaces like caterpillars, the researchers demonstrate. As they report, they have also already developed a small voltage generator module that can be attached to the structures using magnetic force, thus enabling wireless operation.
Another design shows that even more application potential could arise from the connection with additional components: The researchers formed a round configuration from four HEXELs, which was additionally equipped with curved rails using magnetic force. This structure was then able to roll very efficiently. By making jerky movements, this HEXEL robot also easily overcame the unevenness of a sand surface.
Video: Several HEXEL modules combined with curved rails form a robot that can roll over sand and stones. © Darrell J. Irvine
According to the developers, the results show interesting application potential for the concept: “It is far more sustainable to use a reconfigurable robot than to build different robots for different purposes. This can be very beneficial, especially in resource-limited environments,” concludes co-first author Zachary Yoder from MPI-IS.
Source: Max Planck Institute for Intelligent Systems in Stuttgart, specialist article: Science Robotics, doi: 10.1126/scirobotics.adl3546