Origami can enable structures that are compact and lightweight. The facets of an origami structure in traditional designs, however, are essentially nondeformable rigid plates. Therefore, implementing energy storage and robust self-locking in these structures can be challenging. We note that the intricately folded wings of a ladybird beetle can be deployed rapidly and effectively sustain aerodynamic forces during flight; these abilities originate from the geometry and deformation of a specialized vein in the wing of this insect. We report compliant origami inspired by the wing vein in ladybird beetles. The deformation and geometry of the compliant facet enables both large energy storage and self-locking in a single origami joint. On the basis of our compliant origami, we developed a deployable glider module for a multimodal robot. The glider module is compactly foldable, is rapidly deployable, and can effectively sustain aerodynamic forces. We also apply our compliant origami to enhance the energy storage capacity of the jumping mechanism in a jumping robot.

Ladybird beetle–inspired compliant origami

This paper looks to the natural world for solutions to many of the challenges associated with the design of fixed-wing cross-domain vehicles. One example is the common murre, a seabird that flies from nesting locations to feeding areas, dives underwater to catch prey and returns. This hunting expedition provides an outline of a possible mission for a cross-domain vehicle. While the challenges of cross-domain vehicles are many, the focus of this paper was on buoyancy management and propulsion. Potential solutions to each challenge, inspired by multiple animals that cross between aerial and underwater domains, are investigated. From these solutions, three design concepts are considered, a quadrotor/fixed-wing hybrid, a vertical takeoff and landing (VTOL) tailsitter aircraft, and a waterjet-assisted takeoff vehicle. A comparison was made between the capability of each concept to complete two missions based on the common murres' hunting expedition. As a result of this comparison, the VTOL tailsitter design was selected for further study. In-depth design was conducted and a prototype vehicle was built. The completed vehicle prototype successfully conducted submerged operation as well as four air flights. Flights consisted of egress from water, flight in air, ingress into water in each flight, and water locomotion. A total of 11 min, 23 s of flight time was recorded as well as underwater swims down to 12 ft (3.7 m) below the surface.

https://iopscience.iop.org/article/10.1088/1748-3190/aad48b/pdf

Design and demonstration of a seabird-inspired fixed-wing hybrid UAV-UUV system.

Robotic vehicles that are capable of autonomously transitioning between various terrains and fluids have received notable attention in the past decade due to their potential to navigate previously unexplored and/or unpredictable environments. Specifically, aerial-aquatic mobility will enable robots to operate in cluttered aquatic environments and carry out a variety of sensing tasks. One of the principal challenges in the development of such vehicles is that the transition from water to flight is a power-intensive process. At a small scale, this is made more difficult by the limitations of electromechanical actuation and the unfavorable scaling of the physics involved. This paper investigates the use of solid reactants as a combustion gas source for consecutive aquatic jump-gliding sequences. We present an untethered robot that is capable of multiple launches from the water surface and of transitioning from jetting to a glide. The power required for aquatic jump-gliding is obtained by reacting calcium carbide powder with the available environmental water to produce combustible acetylene gas, allowing the robot to rapidly reach flight speed from water. The 160-gram robot could achieve a flight distance of 26 meters using 0.2 gram of calcium carbide. Here, the combustion process, jetting phase, and glide were modeled numerically and compared with experimental results. Combustion pressure and inertial measurements were collected on board during flight, and the vehicle trajectory and speed were analyzed using external tracking data. The proposed propulsion approach offers a promising solution for future high-power density aerial-aquatic propulsion in robotics.

https://robotics.sciencemag.org/content/robotics/4/34/eaax7330.full-text.pdf

Consecutive aquatic jump-gliding with water-reactive fuel

Design, fabrication, and characterization of a multimodal hybrid aerial underwater vehicle

Aerial–aquatic locomotion would allow a broad array of tasks in robot-enabled environmental monitoring or disaster management. One of the most significant challenges of aerial–aquatic locomotion in mobile robots is finding a propulsion system that is capable of working effectively in both fluids and transitioning between them. The large differences in the density and viscosity of air compared to water means that a single direct propulsion system without adaptability will be inefficient in at least one medium. This paper examines multimodal propeller propulsion using computational tools validated against experimental data. Based on this analysis, we present a novel gearbox enabling an aerial propulsion system to operate efficiently underwater. This is achieved with minimal complexity using a single fixed pitch propeller system, which can change gear underwater by reversing the drive motor, but with the gearing arranged to leave the propeller direction unchanged. This system is then integrated into a small robot, and flights in air and locomotion underwater are demonstrated.

/pdf/efficient-aerial-aquatic-locomotion-with-a-single-propulsion-3a5vk9gnzm.pdf

Efficient Aerial–Aquatic Locomotion With a Single Propulsion System

The ability to move between air and water with miniature robots would allow distributed water sampling and monitoring of a variety of unstructured marine environments, such as coral reefs and coastal areas. To enable such applications, we are developing a new class of aerial-aquatic robots, called Aquatic Micro Aerial Vehicles (AquaMAVs), capable of diving into the water and returning to flight. One of the main challenges in the development of an AquaMAV is the provision of sufficient power density for take-off from the water. In this paper, we present a novel system for powerful, repeatable aquatic escape using acetylene explosions in a 34 g water jet thruster, which expels water collected from its environment as propellant. We overcome the miniaturisation problems of combustible fuel control and storage by generating acetylene gas from solid calcium carbide, which is reacted with enviromental water. The produced gas is then combusted in air in a valveless combustion chamber to produce over 20 N of thrust, sufficient to propel small robots into the air from water. The system for producing combustible gases from solid fuels is a very compact means of gas storage, and can be applied to other forms of pneumatic actuation and inflatable structure deployment.

Grant Kennedy

Papers

Consecutive aquatic jump-gliding with water-reactive fuel

High-Power Propulsion Strategies for Aquatic Take-off in Robotics