Insect-scale Robot Research Articles

Low-voltage-driven, insect-scale robots built with opto-mechanical nano-muscle fibers

Low-voltage-driven, insect-scale robots built with opto-mechanical nano-muscle fibers

Spines and Inclines: Bioinspired Spines on an Insect-Scale Robot Facilitate Locomotion on Rough and Inclined Terrain.

To navigate complex terrains, insects use diverse tarsal structures (adhesive pads, claws, spines) to reliably attach to and locomote across substrates. This includes surfaces of variable roughness and inclination, which often require reliable transitions from ambulatory to scansorial locomotion. Using bioinspired physical models as a means for comparative research, our study specifically focused on the diversity of tarsal spines, which facilitate locomotion via frictional engagement and shear force generation. For spine designs, we took inspiration from ground beetles (Family Carabidae), which is a largely terrestrial group known for their quick locomotion. Evaluating four different species, we found that the hind legs host linear rows of rigid spines along the entire tarsus. By taking morphometric measurements of the spines, we highlighted parameters of interest (e.g., spine angle and aspect ratio) in order to test their relationship to shear forces sustained during terrain interactions. We systematically evaluated these parameters using spines cut from stainless steel shim attached to a small acrylic sled loaded with various weights. The sled was placed on 3D-printed models of rough terrain, randomly generated using fractal Brownian motion, while a motorized pulley system applied force to the spines. A force sensor measured the reaction force on the terrain, recording shear force before failure occurred. Initial shear tests highlighted the importance of spine angle, with bioinspired anisotropic designs producing higher shear forces. Using this data, we placed the best (50○ angle) and worst (90○ angle) performing spines on the legs of our insect-scale ambulatory robot physical model. We then tested the robot on various surfaces at 0, 10 and 20○ inclines, seeing similar success with the more bioinspired spines.

Insect-Scale Biped Robots Based on Asymmetrical Friction Effect Induced by Magnetic Torque.

Multimodal and controllable locomotion in complex terrain is of great importance for practical applications of insect-scale robots. Robust locomotion plays a particularly critical role. In this study, a locomotion mechanism for magnetic robots based on asymmetrical friction effect induced by magnetic torque is revealed and defined. The defined mechanism overcomes the design constraints imposed by both robot and substrate structures, enabling the realization of multimodal locomotion on complex terrains. Drawing inspiration from human walking and running locomotion, a biped robot based on the mechanism is proposed, which not only exhibits rapid locomotion across substrates with varying friction coefficients but also achieves precise locomotion along patterned trajectories through programmed controlling. Furthermore, apart from its exceptional locomotive capabilities, the biped robot demonstrates remarkable robustness in terms of load-carrying and weight-bearing performance. The presented locomotion and mechanism herein introduce a novel concept for designing magnetic robots while offering extensive possibilities for practical applications in insect-scale robotics.

Synergistical Mechanical Design and Function Integration for Insect-Scale On-Demand Configurable Multifunctional Soft Magnetic Robots.

Meso- or micro-scale(or insect-scale) robots that are capable of realizing flexible locomotion and/or carrying on complex tasks in a remotely controllable manner hold great promise in diverse fields, such as biomedical applications, unknown environment exploration, in situ operation in confined spaces, and so on. However, the existing design and implementation approaches for such multifunctional, on-demand configurable insect-scale robots are often focusing on their actuation or locomotion, while matched design and implementation with synergistic actuation and function modules under large deformation targeting varying task/target demands are rarely investigated. In this study, through systematical investigations on synergistical mechanical design and function integration, we developed a matched design and implementation method for constructing multifunctional, on-demand configurable insect-scale soft magnetic robots. Based on such a method, we report a simple approach to construct soft magnetic robots by assembling various modules from the standard part library together. Moreover, diverse soft magnetic robots with desirable motion and function can be (re)configured. Finally, we demonstrated (re)configurable soft magnetic robots shifting into different modes to adapt and respond to varying scenarios. The customizable physical realization of complex soft robots with desirable actuation and diverse functions can pave a new way for constructing more sophisticated insect-scale soft machines that can be applied to practical applications soon.

Insect-scale robots powered by combustion

Insect-scale robots powered by combustion

Miniature soft jumping robots made by additive manufacturing

Abstract Fleets of insect-scale robots could navigate space-constrained environments for future applications in agriculture and maintenance. Long distance jumping expands the mobility of small robots. However, the performance of miniature jumpers is hindered by small-scale manufacturing processes and the limited library of design rules, materials, and actuators available at that scale. The intricate components in these robots are produced by manual assembly of miniature components, which imposes design constraints and causes mass inefficiency, reducing the overall system performance. Here, we combine bioinspired kinematic design, coiled artificial muscle actuators, and projection additive manufacturing (AM) to produce a monolithic elastomeric robot design. The fully elastomeric design, inspired by the kinematics of the locust jumping mechanism, can store elastic energy throughout the robot body before releasing it in the form of jumping kinetic energy, thus offering high energy storage density, miniaturization, and lightweight. Enabled by high-speed, production-grade AM, we designed and tested a fleet of 108 robot designs. The smallest tested robot has a length of 7.5 mm, a mass of 0.216 g, and jumps 60 times its body size in horizontal distance. A reduced-order model is developed to predict the compliant robot jumping distance, which agrees well with the experimental results. The jumping is driven by onboard coiled artificial muscles connected to a latch-triggering mechanism. Moreover, the robot can jump while carrying an integrated control system and power source to enable self-triggered jumping. A proof-of-concept motor-driven launch base is used to store large elastic energy in the robot. Overall, the combination of elastomeric AM, coiled artificial muscles, and an integrated triggering mechanism enables the production of fleets of high-performing miniature jumping robots.

S2worm: A Fast-Moving Untethered Insect-Scale Robot With 2-DoF Transmission Mechanism

Designing terrestrial insect-scale robot with high maneuverability and autonomy is becoming an essential challenge in the field of robotics research. Previous work has indicated that compact transmission and integrated control devices can improve the application potential. In this work, an untethered insect-scale inchworm robot is designed and fabricated by using screw theory and smart composite microstructure method, and is named S²worm. The robot weighs 4.34 g and spans 4.1 cm in length. The robot is equipped with custom designed onboard control system and high voltage boost converter to provide the driving signal for the piezoelectric bending actuator. Attributing to the novel transmission mechanism with two degrees of freedom designed based on screw theory, the S²worm can be fabricated through the smart composite microstructure method easily and shows high mobility such as high crawling speed (27.4 cm/s, 6.7 body length/s) and small turning radius (1.7 cm, 0.4 body length/s). The S²worm holds the following advantages: small size, untethered, high mobility and low energy consumption. The robot is promising for application in planetary exploration, earthquake search and constructing insect-scale multi-robot system.

An insect-scale robot reveals the effects of different body dynamics regimes during open-loop running in feature-laden terrain

The transition from the lab to natural environments is an archetypal challenge in robotics. While larger robots can manage complex limb–ground interactions using sensing and control, such strategies are difficult to implement on small platforms where space and power are limited. The Harvard Ambulatory Microrobot (HAMR) is an insect-scale quadruped capable of effective open-loop running on featureless, hard substrates. Inspired by the predominantly feedforward strategy of rapidly-running cockroaches on uneven terrain (Sponberg, 2007), we used HAMR to explore open-loop running on two 3D printed heterogeneous terrains generated using fractional Brownian motion. The ‘pocked’ terrain had foot-scale features throughout while the ‘jagged’ terrain features increased in height in the direction of travel. We measured the performance of trot and pronk gaits while varying limb amplitude and stride frequency. The frequencies tested encompassed different dynamics regimes: body resonance (10–25 Hz) and kinematic running (30–40 Hz), with dynamics typical of biological running and walking, respectively, and limb-transmission resonance (45–60 Hz). On the featureless and pocked terrains, low mechanical cost-of-transport (mCoT) kinematic running combinations performed best without systematic differences between trot and pronk; indicating that if terrain features are not too tall, a robot can transition from homo-to heterogeneous environments in open-loop. Pronk bypassed taller features than trot on the jagged terrain, and higher mCoT, lower frequency running was more often effective. While increasing input power to the robot improved performance in general, lower frequency pronking on jagged terrain allowed the robot to bypass taller features compared with the same input power at higher frequencies. This was correlated with the increased variation in center-of-mass orientation occurring at frequencies near body resonance. This study established that appropriate choice of robot dynamics, as mediated by gait, frequency, and limb amplitude, can expand the terrains accessible to microrobots without the addition of sensing or closed-loop control.

Feedback Altitude Control of a Flying Insect–Computer Hybrid Robot

Unlike biomimetic methods, the insect–computer hybrid is an alternative approach to developing insect-scale robots. Insect–computer hybrid is a technique that transforms a living insect into a controllable robot by embedding it with artificial devices. In this article, a beetle ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Mecynorrhina torquata</i> ) was transformed into a hybrid flying system by mounting an electronic backpack and implanting electrodes on it. Wing trajectories during fictive flight climbing and flight diving were captured to investigate the natural flight-height control of beetles. Compare with the electrically induced wing trajectories via basalar, subalar, and third axillary (3Ax) muscle stimulations, we hypothesized that the basalar muscles are involved in ascending flight, whereas the 3Ax muscles function to reduce the flight-height. By reproducing the electrical stimulations on bilateral muscle pairs during free flights, we found that stimulations of the basalar muscle pair increased vertical accelerations. In contrast, the 3Ax muscle pair's stimulation decreased vertical accelerations gradually as a function of the electrical stimulation frequency. Accordingly, a proportional-derivative feedback controller was proposed to maintain the beetles' flight-height using frequency-dependent electrical pulses on the basalar and 3Ax muscles. In this article, the altitude control of a free-flying beetle was demonstrated for the first time.

Moisture induced electricity for self-powered microrobots

Sustainable operation of microrobots mandatorily needs a continuous supply of energy, which is usually provided by a battery. However, with the miniaturization of the microrobot, the reduction of weight, and the limited lifetime of battery, self-powering of microrobot is a key challenge. Inspired by the crawling of cockroaches, we present an untethered insect-scale robot driven by moisture induced electric power. A moisture-based energy harvesting device has been exploited and embedded in the microrobot, which can capture and store atmospheric water under various environmental conditions through a hygroscopic gel and generate electricity based on redox reaction. The device produces an output voltage of ~1.4 V and an output current of ~43 mA. A combination of moisture-electricity powered vertical vibration and the asymmetric structural design of the microrobot enables its forward locomotion at an average speed of ~4.01 cm/s. Our work could facilitate multifunctionality in future self-powered microrobots and mesoscale devices.

Owlet

Miniaturization is an inherent trend in ubiquitous computing. Insect-scale robots add new capabilities to disaster management, tiny headphones are emerging as complete computing devices, and small wearable health monitors can track vital signs around the clock. Advancements in sensing technologies play a pivotal role in this development. Spatial sensing at this form factor, however, is a skill yet to be mastered, particularly at low-frequency signals like audible sounds. Traditionally, spatial sensing requires sampling in both time and space using an array of microphones, which comes with a strict size requirement and multiplies its power requirement. In this article, we explore the possibility of an alternative design for spatial sensing for miniaturized and power-constrained devices.

Printed miniature robotic actuators with curvature-induced stiffness control inspired by the insect wing

Stimuli-responsive actuating materials offer a promising way to power insect-scale robots, but a vast majority of these material systems are too soft for load bearing in different applications. While strategies for active stiffness control have been developed for humanoid-scale robots, for insect-scale counterparts for which compactness and functional complexity are essential requirements, these strategies are too bulky to be applicable. Here, we introduce a method whereby the same actuating material serves not only as the artificial muscles to power an insect-scale robot for load bearing, but also to increase the robot stiffness on-demand, by bending it to increase the second moment of area. This concept is biomimetically inspired by how insect wings stiffen themselves, and is realized here with manganese dioxide as a high-performing electrochemical actuating material printed on metallized polycarbonate films as the robot bodies. Using an open-electrodeposition printing method, the robots can be rapidly fabricated in one single step in ∼15 minutes, and they can be electrochemically actuated by a potential of ∼1 V to produce large bending of ∼500° in less than 5 s. With the stiffness enhancement method, fast (∼5 s) and reversible stiffness tuning with a theoretical increment by ∼4000 times is achieved in a micro-robotic arm at ultra-low potential input of ∼1 V, resulting in an improvement in load-bearing capability by about 4 times from ∼10 μN to ∼41 μN.

Yaw Control of a Hovering Flapping-Wing Aerial Vehicle With a Passive Wing Hinge

Flapping-wing insect-scale robots (<;$500 mg) rely on small changes in drive signals supplied to actuators to generate angular torques. Previous results on vehicles with passive wing hinges have demonstrated roll, pitch, and position control, but they have not yet been able to control their yaw (heading) angle while hovering. To actuate yaw, the speed of the downstroke can be changed relative to the upstroke by adding a second harmonic signal at double the fundamental flapping frequency. Previous work has shown that pitching dynamics of a passive spring-like wing hinge reduces the aerodynamic drag available to produce yaw torque. We introduce three innovations that increase yaw actuation torque: 1) a new two-actuator robot fly design that increases the moment arm, 2) wider actuators that increase the operating frequency, and 3) a phase shift to the second harmonic signal. We validated these results through simulation and experiment. Further, we present the first demonstration of yaw angle control on a passive-hinge vehicle in a controlled flight. Our new robot fly design, UW Robofly-Expanded, weighs 160 mg (two toothpicks) and requires only two piezo actuators to steer itself.

Robots fuel up

Microrobots Batteries are a convenient source of energy for untethered miniature robots. However, the low specific energy of small-scale batteries sets limits on how long such a robot can operate. Yang et al. report an insect-scale robot called RoBeetle that is powered by the controlled catalytic combustion of methanol, a fuel with more than 10 times the specific energy of a small-scale battery. RoBeetle, with size and mass comparable to a small insect, can carry payloads of up to 2.6 times its body weight, crawl on rough surfaces, and ascend inclines of 15 degrees. Sci. Robot. 5 , eaba0015 (2020).

Integrating chemical fuels and artificial muscles for untethered microrobots.

Continued development of untethered insect-scale robots will require codesigned power and actuation strategies.

Wireless steerable vision for live insects and insect-scale robots.

Vision serves as an essential sensory input for insects but consumes substantial energy resources. The cost to support sensitive photoreceptors has led many insects to develop high visual acuity in only small retinal regions and evolve to move their visual systems independent of their bodies through head motion. By understanding the trade-offs made by insect vision systems in nature, we can design better vision systems for insect-scale robotics in a way that balances energy, computation, and mass. Here, we report a fully wireless, power-autonomous, mechanically steerable vision system that imitates head motion in a form factor small enough to mount on the back of a live beetle or a similarly sized terrestrial robot. Our electronics and actuator weigh 248 milligrams and can steer the camera over 60° based on commands from a smartphone. The camera streams "first person" 160 pixels-by-120 pixels monochrome video at 1 to 5 frames per second (fps) to a Bluetooth radio from up to 120 meters away. We mounted this vision system on two species of freely walking live beetles, demonstrating that triggering image capture using an onboard accelerometer achieves operational times of up to 6 hours with a 10-milliamp hour battery. We also built a small, terrestrial robot (1.6 centimeters by 2 centimeters) that can move at up to 3.5 centimeters per second, support vision, and operate for 63 to 260 minutes. Our results demonstrate that steerable vision can enable object tracking and wide-angle views for 26 to 84 times lower energy than moving the whole robot.

Inverted and Inclined Climbing Using Capillary Adhesion in a Quadrupedal Insect-Scale Robot

Many insects demonstrate remarkable locomotive capabilities on inclined or even inverted surfaces. Achieving inverted locomotion is a challenge for legged insect-scale robots because repeated attachment and detachment to a surface usually requires the design of special climbing gaits, adhesion mechanisms, sensing, and feedback control. In this study, we propose a novel adhesion method that leverages capillary and lubrication effects to achieve simultaneous adhesion and sliding. We design a 47 mg adhesion pad and install it on a 1.4 g insect-scale quadrupedal robot to demonstrate locomotion on inverted and inclined surfaces. On an inverted acrylic surface, the robot's climbing and turning speeds are 0.3 cm/s and 23.6 °/s, respectively. Further, the robot can climb a 30° inclined acrylic surface at 0.04 cm/s. This light-weight, passively stable, and versatile adhesion design is suitable for insect-scale robots with limited sensing, actuation, and control capabilities.

Designing minimal and scalable insect-inspired multi-locomotion millirobots.

In ant colonies, collectivity enables division of labour and resources1-3 with great scalability. Beyond their intricate social behaviours, individuals of the genus Odontomachus4, also known as trap-jaw ants, have developed remarkable multi-locomotion mechanisms to 'escape-jump' upwards when threatened, using the sudden snapping of their mandibles5, and to negotiate obstacles by leaping forwards using their legs6. Emulating such diverse insect biomechanics and studying collective behaviours in a variety of environments may lead to the development of multi-locomotion robotic collectives deployable in situations such as emergency relief, exploration and monitoring7; however, reproducing these abilities in small-scale robotic systems with simple design and scalability remains a key challenge. Existing robotic collectives8-12 are confined to two-dimensional surfaces owing to limited locomotion, and individual multi-locomotion robots13-17 are difficult to scale up to large groups owing to the increased complexity, size and cost of hardware designs, which hinder mass production. Here we demonstrate an autonomous multi-locomotion insect-scale robot (millirobot) inspired by trap-jaw ants that addresses the design and scalability challenges of small-scale terrestrial robots. The robot's compact locomotion mechanism is constructed with minimal components and assembly steps, has tunable power requirements, and realizes five distinct gaits: vertical jumping for height, horizontal jumping for distance, somersault jumping to clear obstacles, walking on textured terrain and crawling on flat surfaces. The untethered, battery-powered millirobot can selectively switch gaits to traverse diverse terrain types, and groups of millirobots can operate collectively to manipulate objects and overcome obstacles. We constructed the ten-gram palm-sized prototype-the smallest and lightest self-contained multi-locomotion robot reported so far-by folding a quasi-two-dimensional metamaterial18 sandwich formed of easily integrated mechanical, material and electronic layers, which will enable assembly-free mass-manufacturing of robots with high task efficiency, flexibility and disposability.

Monolithic fabrication of an insect‐scale self‐lifting flapping‐wing robot

Robots on the order of insect-scale are difficult to manufacture using MEMS technologies for sub-millimetre structures or conventional methods for large devices beyond centimetres. This work presents an electromagnetically driven, monolithically fabricated, insect-scale self-lifting flapping-wing robot for the first time. This robot is created using a simple monolithic method, by which most of the components are integrated and fabricated from a single sheet. Finally, the monolithic insect-scale flapping-wing robot can generate sufficient lift to take off.

A biologically inspired, flapping-wing, hybrid aerial-aquatic microrobot.

From millimeter-scale insects to meter-scale vertebrates, several animal species exhibit multimodal locomotive capabilities in aerial and aquatic environments. To develop robots capable of hybrid aerial and aquatic locomotion, we require versatile propulsive strategies that reconcile the different physical constraints of airborne and aquatic environments. Furthermore, transitioning between aerial and aquatic environments poses substantial challenges at the scale of microrobots, where interfacial surface tension can be substantial relative to the weight and forces produced by the animal/robot. We report the design and operation of an insect-scale robot capable of flying, swimming, and transitioning between air and water. This 175-milligram robot uses a multimodal flapping strategy to efficiently locomote in both fluids. Once the robot swims to the water surface, lightweight electrolytic plates produce oxyhydrogen from the surrounding water that is collected by a buoyancy chamber. Increased buoyancy force from this electrochemical reaction gradually pushes the wings out of the water while the robot maintains upright stability by exploiting surface tension. A sparker ignites the oxyhydrogen, and the robot impulsively takes off from the water surface. This work analyzes the dynamics of flapping locomotion in an aquatic environment, identifies the challenges and benefits of surface tension effects on microrobots, and further develops a suite of new mesoscale devices that culminate in a hybrid, aerial-aquatic microrobot.