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Many soft robots are capable of significantly changing their shape, an ability that can offer advantages in many applications. For instance, such a robot can flatten its body to fit under small gaps and expand to move over large obstacles. Further, because these shape changes are usually driven by a pressurized fluid, if they act over a large area, they have the potential to apply large forces to the world. However, when these same shape changes are used for the locomotion of an untethered robot, they tend to result in slow forward movement. Here we present a hybrid soft-rigid elongated-sphere robot that decouples shape change from locomotion. Pairing a compliant, inflatable outer skin, which changes volume by 15x to both fit under and roll over obstacles and can lift objects up to 30 kg, with a wheeled internal carriage, we obtain relatively fast locomotion. A new two-sided controllable adhesive between the internal carriage and the skin enables the carriage to climb vertically inside the skin, allowing the robot to climb external obstacles. We present the design of the robot, simple modeling of its behavior, and experimental testing. Our work advances the area of hybrid soft-rigid robotics by demonstrating how leveraging the strengths of both soft and rigid systems can have quantifiable performance benefits. 

Modular soft robots combine the strengths of two traditionally separate areas of robotics. As modular robots, they can show robustness to individual failure and reconfigurability; as soft robots, they can deform and undergo large shape changes in order to adapt to their environment, and have inherent human safety. However, for sensing and communication these robots also combine the challenges of both: they require solutions that are scalable (low cost and complexity) and efficient (low power) to enable collectives of large numbers of robots, and these solutions must also be able to interface with the high extension ratio elastic bodies of soft robots. In this work, we seek to address these challenges using acoustic signals produced by piezoelectric surface transducers that are cheap, simple, and low power, and that not only integrate with but also leverage the elastic robot skins for signal transmission. Importantly, to further increase scalability, the transducers exhibit multi-functionality made possible by a relatively flat frequency response across the audible and ultrasonic ranges. With minimal hardware, they enable directional contact-based communication, audible-range communication at a distance, and exteroceptive sensing. We demonstrate a subset of the decentralized collective behaviors these functions make possible with multi-robot hardware implementations. The use of acoustic waves in this domain is shown to provide distinct advantages over existing solutions. 

As robotic technologies advance and robots move out of factories and labs into the real world, grip on a variety of surfaces (e.g. smooth or rough) in a variety of conditions (e.g. dry or wet) becomes increasingly important. Bioinspired “microspines” have been previously explored, but primarily for vertical climbing applications or for small-scale robots applying low forces (less than 1 N). Further, these works primarily focused on rough surfaces. To advance this area of research, we present a composite material comprising high- friction rubber and compliant nitinol microspines which can passively retract below the surface of the rubber. We show that the composite can support large loads (greater than 75 N) with a high coefficient of friction on both smooth and rough surfaces (μ > 1.1), outperforming microspines alone on smooth surfaces and rubber alone on rough surfaces, especially when wet and oily. Further, due to the retraction of the microspines, the composite does not damage relatively soft, smooth surfaces, like wood flooring. We also test durability, and show that it is improved by microspine compliance, and test the effects of varying microspine diameter, angle, and tip shape. Finally, we demonstrate that a small RC car can climb steeper slopes and stop more quickly in wet conditions with microspines. 

For robots to be useful for real-world applications, they must be safe around humans, be adaptable to their environment, and operate in an untethered manner. Soft robots could potentially meet these requirements; however, existing soft robotic architectures are limited by their ability to scale to human sizes and operate at these scales without a tether to transmit power or pressurized air from an external source. Here, we report an untethered, inflated robotic truss, composed of thin-walled inflatable tubes, capable of shape change by continuously relocating its joints, while its total edge length remains constant. Specifically, a set of identical roller modules each pinch the tube to create an effective joint that separates two edges, and modules can be connected to form complex structures. Driving a roller module along a tube changes the overall shape, lengthening one edge and shortening another, while the total edge length and hence fluid volume remain constant. This isoperimetric behavior allows the robot to operate without compressing air or requiring a tether. Our concept brings together advantages from three distinct types of robots—soft, collective, and truss-based—while overcoming certain limitations of each. Our robots are robust and safe, like soft robots, but not limited by a tether; are modular, like collective robots, but not limited by complex subunits; and are shape-changing, like truss robots, but not limited by rigid linear actuators. We demonstrate two-dimensional (2D) robots capable of shape change and a human-scale 3D robot capable of punctuated rolling locomotion and manipulation, all constructed with the same modular rollers and operating without a tether. 

A fundamental challenge in the field of modular and collective robots is balancing the trade-off between unit- level simplicity, which allows scalability, and unit-level function- ality, which allows meaningful behaviors of the collective. At the same time, a challenge in the field of soft robotics is creating untethered systems, especially at a large scale with many controlled degrees of freedom (DOF). As a contribution toward addressing these challenges, here we present an untethered, soft cellular robot unit. A single unit is simple and one DOF, yet can increase its volume by 8x and apply substantial forces to the environment, can modulate its surface friction, and can switch its unit-to-unit cohesion while agnostic to unit-to- unit orientation. As a soft robot, it is robust and can achieve untethered operation of its DOF. We present the design of the unit, a volumetric actuator with a perforated strain-limiting fabric skin embedded with magnets surrounding an elastomeric membrane, which in turn encompasses a low-cost micro-pump, battery, and control electronics. We model and test this unit and show simple demonstrations of three-unit configurations that lift, crawl, and perform plate manipulation. Our untethered, soft cellular robot unit lays the foundation for new robust soft robotic collectives that have the potential to apply human-scale forces to the world.