Wireless Soft Robots Inch Closer to Confined-Space Exploration

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Author: Denis Avetisyan

Researchers have developed a wirelessly powered, thin-film soft robot capable of untethered locomotion, opening new possibilities for minimally invasive robotics and remote inspection.

This review details the design, fabrication, and performance of a low-voltage dielectric elastomer actuator-driven soft robot achieving a speed of 0.5 mm/s.

Confined space robotics often demands both miniaturization and untethered operation, presenting a significant engineering challenge. This is addressed in ‘Untethered thin dielectric elastomer actuated soft robot’, which details the development of a wirelessly powered, thin-film soft robot propelled by low-voltage dielectric elastomer actuators. The resulting prototype-measuring just 38mm in length and weighing 2.34g-achieves a locomotion speed of 0.5 mm/s and demonstrates feasibility for navigating complex environments. Could this approach pave the way for a new generation of adaptable robots capable of accessing previously unreachable spaces?

Breaking the Tether: The Pursuit of True Robotic Mobility

Many robotic systems historically depend on a continuous physical connection – a tether – to an external power supply. While providing a reliable energy source, this reliance fundamentally restricts a robot’s operational scope and accessibility. The tether limits movement within the workspace, preventing entry into confined or obstructed areas such as collapsed buildings, narrow pipelines, or complex machinery. This constraint poses significant challenges for applications requiring exploration, inspection, or intervention in environments where physical access is difficult or dangerous. Consequently, the development of untethered robotic solutions-those capable of independent, self-contained operation-represents a crucial step towards expanding the utility and versatility of robotic technology across diverse fields.

Fully untethered robotic movement demands a fundamental shift in how robots are powered and controlled. Researchers are actively developing onboard power sources – moving beyond bulky batteries to explore options like energy harvesting from vibrations or light, and high-density fuel cells. Simultaneously, advancements in actuation are crucial; traditional motors can be power-hungry, so innovations in materials like shape-memory alloys, dielectric elastomers, and compact hydraulic systems offer alternatives. These developments aren’t simply about shrinking components; they necessitate integrated designs where power management and motor control are optimized as a single system, allowing for prolonged, independent operation in complex and previously inaccessible environments. The ultimate goal is a robot capable of sustained, agile movement without external constraints, opening doors to applications in search and rescue, environmental monitoring, and even space exploration.

The pursuit of genuinely mobile robots hinges on a delicate balance between power requirements and physical footprint. Achieving compact agility necessitates a radical focus on miniaturization and energy efficiency in all onboard systems. Researchers are actively developing micro-batteries, high-density capacitors, and innovative power management circuits to minimize weight and volume while maximizing operational duration. Simultaneously, advancements in actuator design – exploring materials like shape-memory alloys and micro-fabricated motors – aim to deliver substantial force and precision within severely constrained spaces. This synergistic approach – shrinking power sources and optimizing actuation – is not merely about reducing size; it’s about fundamentally altering what’s possible in robotic exploration, inspection, and manipulation, allowing robots to navigate complex environments and perform intricate tasks previously inaccessible to larger, tethered machines.

The TS-DEA: A Miniature Muscle for Confined Spaces

The Thin Soft Dielectric Elastomer Actuator (TS-DEA) provides a compact actuation solution specifically designed for applications in soft robotics where space is limited and rapid response times are required. Utilizing dielectric elastomer films, the TS-DEA achieves a low profile due to its thin construction, enabling integration into constrained environments. This design prioritizes high-frequency performance, allowing for quick and precise movements essential for tasks such as gripping, bending, or locomotion in soft robotic systems. The actuator’s characteristics address the need for lightweight and dynamically responsive components within the field of soft robotics, distinguishing it from traditional rigid actuation methods.

The TS-DEA achieves high deformation with a small footprint through a dual-actuation, sandwiched structure. This design incorporates a compressible tensioning mechanism which pre-stresses the dielectric elastomer, enabling larger strains than conventional DEAs. This pre-stress effectively reduces the elastomer’s tendency to buckle under actuation, maximizing usable displacement. The layered construction also minimizes overall device thickness by distributing stress across multiple elastomer films, contributing to a low-profile form factor suitable for integration into constrained spaces.

The TS-DEA utilizes dielectric elastomers, materials characterized by high permittivity and low elastic modulus, resulting in a substantial energy density of approximately 2.3 x $10^6$ J/m³. This property allows the actuator to deliver significant force and displacement despite its small physical dimensions. Specifically, the fabricated TS-DEA demonstrates a capacitance of 1.69 nF, which, when combined with applied voltage, facilitates rapid charge storage and discharge, contributing to the actuator’s high-frequency performance and power output. The high energy density minimizes the required volume of the elastic material, directly contributing to the compact design of the TS-DEA.

Deconstructing the System: Fabrication and Integration

Dielectric elastomer layers were fabricated utilizing spin coating, a process that deposits a uniform thin film across a substrate. Following deposition, biaxial stretching was implemented to enhance material performance characteristics. This stretching process introduces alignment of polymer chains, increasing the dielectric constant and improving the elastomer’s ability to deform under an applied electric field. The resulting material exhibited improved electromechanical coupling, allowing for greater actuation strain and force compared to unstretched films. Precise control of the spin coating parameters and stretching ratios were critical to achieving consistent layer thickness and optimized performance metrics.

The system’s onboard electronics were specifically designed to meet the substantial voltage requirements of the Twisted String Dielectric Elastomer Actuator (TS-DEA). A flexible printed circuit board (PCB) was implemented to minimize weight and enable integration with the deformable elastomer. Crucially, a flyback converter circuit was incorporated to efficiently step-up a lower input voltage to the 220V necessary for TS-DEA actuation. This converter topology was chosen for its high voltage output capability and relatively compact size, allowing for a fully integrated and self-contained robotic system without external high-voltage sources.

The complete robotic platform integrates a Twisted String Dielectric Elastomer Actuator (TS-DEA) with all necessary power delivery components, resulting in a self-contained and untethered system. This design eliminates the need for external power or control connections, enabling independent operation. The system’s onboard electronics, including a flexible printed circuit board and flyback converter, provide the 220V required to drive the TS-DEA. Operational testing confirmed a resonant frequency of 86 Hz, characterizing the dynamic performance of the fully integrated robotic platform.

Beyond the Prototype: Performance and the Road Ahead

Experimental results demonstrate a significant correlation between power source and robotic performance in the TS-Robot. When operating in a tethered configuration – receiving power directly from an external source – the robot achieved a locomotion speed of 12.36 mm/s. However, transitioning to a completely untethered, self-powered mode resulted in a substantial decrease in speed, down to 0.5 mm/s. This disparity underscores the considerable energy demands of onboard power systems, specifically batteries or fuel cells, and their impact on overall efficiency and achievable velocity. The weight and inherent energy losses associated with these self-contained power solutions currently present a limiting factor, driving ongoing research into optimized power management strategies and lighter-weight energy storage alternatives.

The TS-Robot’s remarkably small physical profile-a key design consideration-opens doors to environments inaccessible to larger robotic systems. This low-profile architecture allows the robot to navigate and operate within constricted spaces, such as narrow pipes, ventilation shafts, or the interiors of complex machinery. Consequently, potential applications extend beyond open-area locomotion to include detailed inspection of infrastructure, search and rescue operations in collapsed structures, and the exploration of previously unreachable areas in environmental monitoring or disaster response. The ability to access these confined spaces provides a distinct advantage, offering a non-destructive means of data collection and intervention where traditional methods are impractical or impossible.

Currently, the TS-Robot operates with an energy efficiency of just 0.1%, a figure that underscores a primary focus of ongoing development. Researchers are actively investigating advanced power management strategies, including minimizing parasitic losses and implementing more intelligent energy allocation algorithms. Simultaneously, exploration into novel materials – prioritizing those with superior strength-to-weight ratios and enhanced energy storage capabilities – is underway. These combined efforts aim to significantly improve both the robot’s speed and operational endurance, potentially unlocking more complex and sustained missions in confined or challenging environments. Improving energy efficiency is not merely about extending battery life; it’s crucial for reducing the overall weight and size of onboard power sources, further enhancing the robot’s maneuverability and accessibility.

The pursuit of untethered locomotion, as demonstrated by this research into thin dielectric elastomer actuators, isn’t simply about building a robot; it’s about probing the limits of material behavior and control. One contemplates the inherent assumptions within robotic design itself. As Andrey Kolmogorov observed, “The most important things are not those that are easy to express.” This sentiment resonates deeply. The challenge wasn’t merely to make a robot move wirelessly, but to do so with low voltage and minimal material, forcing a re-evaluation of established actuation methods. The team effectively sought what appears to be a ‘bug’ – the constraints of traditional robotics – and discovered a signal: a novel approach to confined-space navigation.

Where Do We Go From Here?

The demonstration of untethered locomotion, however modest at 0.5 mm/s, exposes the inherent limitations of current actuator design more acutely than any performance benchmark. The system functions – it moves – but the energy cost of that movement reveals a fundamental trade-off. Every exploit starts with a question, not with intent, and the question here is not simply ‘can it move?’, but ‘at what cost, and with what efficiency?’. Future work will inevitably focus on material science – thinner, more responsive dielectrics – but the more interesting challenge lies in architectural innovation. Mimicking biological systems isn’t about replicating complexity; it’s about discovering minimal viable structures.

The current reliance on external power transmission, while enabling untethered operation, introduces a new set of constraints. Truly independent operation demands on-board energy harvesting or storage – a miniaturized power source capable of sustaining actuator operation without compromising the robot’s compliance. This necessitates a shift from viewing the actuator as the primary component to considering the entire system – actuator, power source, and control electronics – as a single, integrated unit.

Ultimately, this work isn’t about building better robots; it’s about deconstructing the very notion of ‘robot’. The pursuit of increasingly soft, compliant, and untethered systems forces a re-evaluation of control paradigms. Traditional robotics relies on precise positioning and rigid structures. This new paradigm demands adaptability, resilience, and a willingness to relinquish control – to allow the robot to navigate its environment through a process of self-organization rather than direct manipulation.

Original article: https://arxiv.org/pdf/2512.17940.pdf

Contact the author: https://www.linkedin.com/in/avetisyan/

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2025-12-23 15:46