ESA: Radiation-resistant caterpillar robot could explore planets

As part of the European Space Agency ESA's Discovery Program for planetary exploration, the University of Gothenburg has developed a motorless, flexible soft robot in the form of a caterpillar that moves similarly to a biological caterpillar. This locomotion approach enables the robot to move in difficult terrain under harsh environmental conditions and to squeeze through narrow gaps, for example.

Soft robots are flexible yet insensitive, allowing them to be used in harsh conditions such as extreme heat, cold, moisture, and radiation. In contrast, rigid robots with joints, driven by electric motors, are not as well-suited. This is because such robots require a certain amount of maintenance, which is not ideal if they need to operate for a long period and cannot be serviced during planetary exploration.

Crawling with a single elastomer actuator

The central component of the caterpillar robot is an actuator. It consists of a dielectric elastomer (Dielectric Elastomer Actuator, DEA) and forms an artificial muscle. The flexible, thin polymer strand is embedded between two compliant electrodes. As soon as a voltage is applied, it contracts radially and expands again. In principle, the actuator behaves similarly to a biological muscle. The advantages: the artificial muscle can deform significantly, react quickly, and efficiently stores and releases energy.

The researchers at the University of Gothenburg use a rolled version of the DEA (Rolled DEA – RDEA) in the caterpillar robot, which can contract and expand axially. This achieves the necessary caterpillar-like movement of the robot. As a result, the robot can not only move forward with a single actuator but also be controlled in all directions without complex control electronics.

To this end, the scientists conducted a series of movement tests on various surfaces made of 3D-printed substrates with groove patterns. The robot's “legs” latched into the patterns, aligning the robot along the groove direction. Systematic experiments with substrates depicting different angles in the groove pattern showed that the robot can be precisely steered left and right, despite having only one actuator. However, to change direction in uncontrolled environments, the robot needs active steering in addition to its passive control.

Durable and low-maintenance

The material used for the caterpillar robot is also quite robust against damage and withstands high and low temperatures. This makes the robot quite low-maintenance. To enable it to perform its duties on other planets, such as Mars, the researchers have made it radiation-resistant to a certain extent. For this purpose, they used flexible electrodes made of single-walled carbon nanotubes (SWCNT) in the actuator. The cylindrical nanomaterial consists of a rolled graphene layer that possesses fault-tolerant properties. It offers protection against physical damage and, to some extent, against Mars radiation, especially against alpha and proton particles with an energy of 10 MeV, according to a simulation.

(olb)