The vision of robotic materials-cohesive collectives of robotic units that can arrange into virtually any form with any physical properties-has long intrigued both science and fiction. Yet, this vision requires a fundamental physical challenge to be overcome: The collective must be strong, to support loads, yet flow, to take new forms. We achieve this in a material-like robotic collective by modulating the interunit tangential forces to control topological rearrangements of units within a tightly packed structure. This allows local control of rigidity transitions between solid and fluid-like states in the collective and enables spatiotemporal control of shape and strength. We demonstrate structure-forming and healing and show the collective supporting 700 newtons (500 times the weight of a robot) before "melting" under its own weight.

Research in the area of photo-actuation is growing rapidly, yet there are few examples of photo-actuators with practical use cases. One potential application is for the control of intelligent electromagnetic surfaces, or two-dimensional arrays that could shape and control an incident electromagnetic field in ideally any manner. A promising concept to realize such a surface leverages signal refraction via antenna edges, but requires non-metal actuation, large antenna rotations, and high antenna angular accuracy for long periods of time. Here, we present a nonmetal, light-controlled, multi-position inchworm actuator array that can rotate an antenna 88 degrees in incremental steps of less than 3.4 degrees with zero-power shape-persistence. The design is modular and rapidly manufacturable via a layered laser-cutting technique, such that the actuator can be tiled into an array to control the rotation of many antennas. We control the array with a single focused IR light that rasters across the actuators to precisely control all antenna positions. We characterize the response time, accuracy, and repeatability of a single actuator, and demonstrate the array achieving diverse antenna configurations. This work advances the precision and scalability of photothermal actuation not only for use in intelligent electromagnetic surfaces but for any application benefitting from light-controlled actuation.

Incorporating compliance into shape-changing displays can improve their wearability and actuation modalities. While recent advances in soft actuators highlight promising paths for soft shape-changing displays, these displays currently face some practical challenges of device failure and limited actuator displacement. A monolithic fabrication processes means the device is challenging to repair, for a single point of failure often renders the whole device ineffective. We have leveraged a modular hyperelastic bubble array layer to create a soft shape-changing skin. The modularity of this device allows for rapid repair of individual bubbles and fast prototyping, and the spherical, hyperelastic actuators enable an increase in degrees of freedom due to bubble-to-bubble interactions. Furthermore, we present a forward kinematic description of our device, incorporating these bubble-to-bubble interactions and the nonlinear instabilities unique to hyperelastic actuator inflation. We demonstrate the utility of this soft shape-changing skin as a haptic display that can be worn comfortably or applied to passive interactive objects such as a computer mouse.

Latch-mediated spring-actuation (LaMSA) is utilized in a majority of jumping robots for its ability to slowly load and quickly release energy to generate high-power movement. Such mechanisms are found in robots that jump off of solid surfaces and even off of water. However, no robot currently employs LaMSA to jump on air. This paper presents the design, modeling, and fabrication of the first LaMSA-driven air jumper, capable of jumping mid-air. Our model informs prototype design and provides insight into the scaling properties of the wing area, wing and fuselage mass, and energy. By successfully applying LaMSA to a new domain, this work lays the foundation for future investigations into high-power air-reaction maneuvers, such as in fixed-wing unmanned aerial vehicle (UAV) flight, by enabling instantaneous changes in altitude without the addition of extra on-board motors.

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 that 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.

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.

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 functionality, 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.

Compact and efficient energy absorption is desirable for numerous applications including manufacturing, transportation, and protective equipment. An ideal shock absorber is a smart material or structure that can adapt its force-displacement properties to minimize the peak impact force regardless of the impact energy. While traditional shock absorbers can produce precisely-tuned ideal force profiles, they are rigid devices that only compress half of their total length, limiting utility in space-constrained applications. Energy absorbers that are soft and collapsible, such as foams, do not have ideal force profiles and generally have insufficient viscoelasticity to adapt to different impact energies. Here, we present a smart structure concept-variable area shock absorption (VASA)-that leverages a changing contact area in a hydraulically damped collapsible system to passively adapt the force to the minimum necessary to absorb the energy of an impact. Using an analytical fluid dynamics model, we derived the contact area as a function of compression to produce a constant force over the entire stroke of a fixed-orifice damper, and validate this concept experimentally using a preliminary 3D-printed prototype. The VASA prototype follows the constant force profile with aNRMSEbetween 0.02-0.25 at impact speeds between 2.3 and 4.3 m s(-1). This new approach for absorbing energy is compatible with full collapse of the absorber, enabling soft devices for space-constrained applications in future work. Potential applications include helmets that must absorb energy at a near-minimum force level across multiple impact energy levels.