Unmanned planetary rovers have traversed kilometers of Lunar and Martian terrain while performing valuable science. However, they still face mobility challenges including steep slopes and unstable soil that can entrap vehicles, as demonstrated by NASA's Spirit rover. Vehicles on Earth can depend on a human operator or rescue vehicle to tow them out of an entrapment, but remote rovers cannot, limiting their route to highly conservative path selections. To increase rover mobility on slopes and unstable soils, we present a resettable anchor launcher for independent self-rescue. The device launches a tethered land anchor away from the rover and then uses a winch to tow the rover up a hill or out of an entrapment. This paper presents the design of the launcher and its integration into a half-meter-long rover mobility platform with field testing at the NASA Glenn Research Center SLOPE Lab. We demonstrate repeatable launching and winching to help the rover climb a 17° slope of loose GRC-1 Lunar regolith simulant that it otherwise could not climb. Our work presents an alternative method to increase rover mobility, especially up slopes, and enables independent rover rescue, which could eventually increase mission duration and reduce risk of entrapment during extraterrestrial exploration.

Robot performance has advanced considerably both in and out of the factory, however in tightly constrained, unknown environments such as inside a jet engine or the human heart, current robots are less adept. In such cases where a borescope or endoscope can’t reach, disassembly or surgery are costly. One promising inspection device inspired by plant growth are "vine robots" that can navigate cluttered environments by extending from their tip. Yet, these vine robots are currently limited in their ability to simultaneously steer into tight curvatures and apply substantial forces to the environment. Here, we propose a plant-inspired method of steering by asymmetrically lengthening one side of the vine robot to enable high curvature and large force application. Our key development is the introduction of an extremely anisotropic, composite, wrinkled film with elastic moduli 400x different in orthogonal directions. The film is used as the vine robot body, oriented such that it can stretch over 120% axially, but only 3% circumferentially. With the addition of controlled layer jamming, this film enables a steering method inspired by plants in which the circumference of the robot is inextensible, but the sides can stretch to allow turns. This steering method and body pressure do not work against each other, allowing the robot to exhibit higher forces and tighter curvatures than previous vine robot architectures. This work advances the abilities of vine robots–and robots more generally–to not only access tightly constrained environments, but perform useful work once accessed.

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 airreaction 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.

Soft, tip-extending, pneumatic "vine robots" that grow via eversion are well suited for navigating cluttered environments. Two key mechanisms that add to the robot’s functionality are a tip-mounted retraction device that allows the growth process to be reversed, and a tip-mounted camera that enables vision. However, previous designs used rigid, relatively heavy electromechanical retraction devices and external camera mounts, which reduce some advantages of these robots. These designs prevent the robot from squeezing through tight gaps, make it challenging to lift the robot tip against gravity, and require the robot to drag components against the environment. To address these limitations, we present a soft, pneumatically driven retraction device and an internal camera mount that are both lightweight and smaller than the diameter of the robot. The retraction device is composed of a soft, extending pneumatic actuator and a pair of soft clamping actuators that work together in an inch-worming motion. The camera mount sits inside the robot body and is kept at the tip of the robot by two low-friction interlocking components. We present characterizations of our retraction device and demonstrations that the robot can grow and retract through turns, tight gaps, and sticky environments while transmitting live video from the tip. Our designs advance the ability of everting vine robots to navigate difficult terrain while collecting data.

Soft robotic pneumatic grippers have been shown to be versatile, robust to impacts, and safe for use on delicate objects. One type, fluidic elastomer grippers, are characterized by fingers with an inextensible gripping surface backed by extensible pneumatic chambers; when inflated, this mismatch in extensibility results in the finger curling. However, one drawback of these simple fingers is that they have one preprogrammed grasp, usually a simple constant-curvature wrap. While well-suited for finger-sized round objects, they do not grasp flat or small objects well. Here, we present an adaptable tri-stable soft robotic finger that can form either a pinch or wrap grasp based on the shape of the grasped object. We enable this by incorporating two bi-stable springs into the inextensible layer. The three stable positions are: i) open (unpressurized), ii) pinch (with only the proximal section bending), and iii) wrap (with the entire finger bending). We present a simple model of the behavior of our finger and experimental results verifying the model. Further, we apply forces and moments to grasped objects, and show that the tri-stable finger increases the grasping performance when compared to a control gripper with equal gripping force. Our work presents a novel design modification that is unobtrusive, simple, and passive. Our introduction of inexpensive programmable hardware advances the versatility and adaptability of soft grippers.

The field of soft robotics is grounded on the idea that, due to their inherent compliance, soft robots can safely interact with the environment. Thus, the development of effective planning and control pipelines for soft robots should incorporate reliable robot-environment interaction models. This strategy enables soft robots to effectively exploit contacts to autonomously navigate and accomplish tasks in the environment. However, for a class of soft robots, namely vine-inspired, tip-extending or "vine" robots, such interaction models and the resulting planning and control strategies do not exist. In this paper, we analyze the behavior of vine robots interacting with their environment and propose an obstacle-interaction model that characterizes the bending and wrinkling deformation induced by the environment. Starting from this, we devise a novel obstacle-interaction planning method for these robots. We show how obstacle interactions can be effectively leveraged to enlarge the set of reachable workspace for the robot tip, and verify our findings with both simulated and real experiments. Our work improves the capabilities of this new class of soft robot, helping to advance the field of soft robotics.

Soft, tip-extending "vine" robots offer a unique mode of inspection and manipulation in highly constrained environments. For practicality, it is desirable that the distal end of the robot can be manipulated freely, while the body remains stationary. However, in previous vine robots, either the shape of the body was fixed after growth with no ability to manipulate the distal end, or the whole body moved together with the tip. Here, we present a concept for shape-locking that enables a vine robot to move only its distal tip, while the body is locked in place. This is achieved using two inextensible, pressurized, tip-extending, chambers that "grow" along the sides of the robot body, preserving curvature in the section where they have been deployed. The length of the locked and free sections can be varied by controlling the extension and retraction of these chambers. We present models describing this shape-locking mechanism and workspace of the robot in both free and constrained environments. We experimentally validate these models, showing an increased dexterous workspace compared to previous vine robots. Our shape-locking concept allows improved performance for vine robots, advancing the field of soft robotics for inspection and manipulation in highly constrained environments.

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.

Soft, tip-extending devices, or “vine robots,” are a promising new paradigm for navigating cluttered and confined environments. Because they lengthen from their tips, there is little relative movement of the body with the environment, and the compressible nature of the device allows it to pass through orifices smaller than its diameter. However, the interaction between these devices and the environment is not well characterized. Here we present a comprehensive mathematical model that describes vine robot behavior during environmental interaction that provides a basis from which informed designs can be generated in future works. The model incorporates transverse and axial buckling modes that result from growing into obstacles with varying surface normals, as well as internal path-dependent and independent resistances to growth. Accordingly, the model is able to predict the pressure required to grow through a given environment due to the interaction forces it experiences. We experimentally validate both the individual components and the full model. Finally, we present three design insights from the model and demonstrate how they each improve performance in confined space navigation. Our work helps advance the understanding of tip-extending, vine robots through quantifying their interactions with the environment, opening the door for new designs and impactful applications in the realms of healthcare, research, search and rescue, and space exploration.

Energy harvesting is an attractive alternative to carrying onboard power for mobile robots, especially for long duration missions. While solar is a powerful option, alternatives are needed for situations where direct sunlight is unavailable. One intriguing concept was proposed in the 17thcentury to power clocks: energy harvesting based on temporal, rather than spatial, temperature gradients, using a low boiling point fluid that vaporizes at ambient temperatures. This concept has many strengths: it offers all-in-one energy harvesting and storage; direct high-force and large displacement mechanical output, eliminating the need for a motor; and temporal gradients are ubiquitous, due to diurnal thermal fluctuations. The challenge for robotic applications, however, is to create large enough amounts of work in a small enough package to power a mobile device while using a non-toxic and readily available working fluid. Here we present a simple, low-cost energy harvesting actuator, powered by the vaporization of butane and isobutane, with an isobaric energy density of up to 38000 J/m3(i.e. energy extracted per total volume expansion) each time the temperature fluctuates 13.1°C, enough to power a small car to drive 10m. Two principles enable this: i) precompression of the working fluid, allowing us to tune the boiling point and choose among many non-toxic fluids that do more work than non-compressed fluids; and ii) a constant force profile of the return springs, allowing more work than a linear spring. We present a simple model of the actuator and experimental results characterizing its behavior. Our work lays the foundation for energy harvesting across temporal temperature gradients using vaporization as a viable option for powering mobile robots.

Mobile robots of all shapes and sizes move through the air, water, and over ground. However, few robots can move through the ground. Not only are the forces resisting movement much greater than in air or water, but the interaction forces are more complicated. Here we propose a soft robotic device that burrows through dry sand while requiring an order of magnitude less force than a similarly sized intruding body. The device leverages the principles of both tip-extension and granular fluidization. Like roots, the device extends from its tip; the principle of tip-extension eliminates skin drag on the sides of the body, because the body is stationary with respect to the medium. We implement this with an everting, pressure-driven thin film body. The second principle, granular fluidization, enables a granular medium to adopt a dynamic fluid-like state when pressurized fluid is passed through it, reducing the forces acting on an object moving through it. We realize granular fluidization with a flow of air through the core of the body that mixes with the medium at the tip. The proposed device could lead to applications such as search and rescue in mudslides or shallow subterranean exploration. Further, because it creates a physical conduit with its body, electrical lines, fluids, or even tools could be passed through this channel.