While many animals exhibit impressive hopping capabilities, machines have struggled to match their performance. Current hopping robots face limitations in power density, energy efficiency, and control stability. Here, we present a parallel-elastic actuation mechanism with a reactive latch that optimizes energy transfer, enabling a legged robot to achieve hopping heights and continuity previously unattainable. This mechanism efficiently stores and releases energy, extending the actuation period over the aerial phase while minimizing stance time. Our robot achieves a maximum hopping height of 3.6 meters, surpassing both human and animal records while demonstrating sustained, high-frequency hopping cycles with minimal power requirement. By integrating inertia-based onboard sensorimotor autonomy, we demonstrate stable, controlled hopping in environments without external aid. These results represent a step toward bridging the performance gap between biological and robotic locomotion, with potential to influence the design of future legged systems.

Mobile robots have revolutionized various fields, offering solutions for manipulation, environmental monitoring, and exploration. However, payload capacity remains a limitation. This paper presents a novel thrust-based robotic hopper capable of carrying payloads up to 9 times its own weight while maintaining agile mobility over less structured terrain. The 220 gram robot carries up to 2 kg while hopping—–a capability that bridges the gap between high-payload ground robots and agile aerial platforms. Key advancements that enable this high-payload capacity include the integration of bidirectional thrusters, allowing for both upward and downward thrust generation to enhance energy management while hopping. Additionally, we present a refined model of dynamics that accounts for heavy payload conditions, particularly for large jumps. To address the increased computational demands, we employ a neural network compression technique, ensuring real-time onboard control. The robot's capabilities are demonstrated through a series of experiments, including leaping over a high obstacle, executing sharp turns with large steps, as well as performing simple autonomous navigation while carrying a 730 g LiDAR payload. This showcases the robot's potential for applications such as mobile sensing and mapping in challenging environments.

Rigid robots can achieve precise motions but expose shortcomings in system complexity, fabrication cost, and humanrobot interaction, which motivates researchers to develop various soft robots to fill these gaps. Electro-hydraulic actuators (EHAs) have received widespread attention and been used in many soft robots due to impressive high-strain, fast-speed and rapidresponse characteristics. However, existing EHAs face challenges in achieving large-deformation, high-robustness, and low-weight simultaneously. This limits the application of EHAs in robotic systems that are weight-sensitive or require fail-safe and faulttolerant behavior. Here, we present a lightweight (0.98 g) electropneumatic actuator (EPA) filled with air and only 0.1-mL liquid dielectric, which achieves high-speed bending from 11° to 93.5° in 60 ms, large-angle bending from 11° to 104° in 2 s (the largest in current EHAs), and high-frequency swing at 20 Hz. The EPA is ultrarobust and can operate properly after being punctured by four needles or crushed twice by a 1500-kg vehicle. Furthermore, to validate the above features of EPAs, three applications are demonstrated at a voltage of 6 kV, including four-finger grippers, fast-crawling robots, and water-walking robots. This work pushes the boundaries of robustness and lightweight for EHAs, providing a foundation for the application of electro-pneumatic actuation in soft robotics.

As drones become interwoven in human activities, increasingly taking on tasks interpreted as creative and performative, such as choreographed light shows, there is emerging interest in understanding how drones and humans can perform together. Humans have different habits when performing with partners as opposed to solo. How do people adapt their behaviors and perspectives when improvising with robotic partners? To explore these questions, we conducted a study investigating dancer-drone interactions using a system of micro aerial vehicles designed to facilitate improvised solo and partnered dances. Through solo and tandem dances with one or two robots, we analyzed the performers’ perceived workflow from semi-structured interviews and quantified their movement patterns during the improvisation. We found that the dancers perceived drone movements through spatial metaphors like the ceiling and gravity, anthropomorphizing drones as props on a stage through position and generated sound. The dancers felt a greater connection in single-drone scenarios and showed heightened avoidance behavior in two-drone situations. Our work shows how a robotic system can energize human dancers to improvise individually and in pairs.

Flying insects are remarkably agile and robust. As they fly through cluttered natural environments, they can demonstrate aggressive acrobatic maneuvers such as backflip, rapid escape, and in-flight collision recovery. Current state-of-the-art subgram microaerial-vehicles (MAVs) are predominately powered by rigid actuators such as piezoelectric ceramics, but they have low fracture strength (120 MPa) and failure strain (0.3%). Although these existing systems can achieve a high lift-to-weight ratio, they have not demonstrated insect-like maneuvers such as somersault or rapid collision recovery. In this article, we present a 665 mg aerial robot that is powered by novel dielectric elastomer actuators (DEA). The new DEA achieves high power density (1.2 kW/kg) and relatively high transduction efficiency (37%). We further incorporate this soft actuator into an aerial robot to demonstrate novel flight capabilities. This insect-scale aerial robot has a large lift-to-weight ratio (>2.2:1) and it achieves an ascending speed of 70 cm/s. In addition to demonstrating controlled hovering flight, it can recover from an in-flight collision and perform a somersault within 0.16 s. This work demonstrates that soft aerial robots can achieve insect-like flight capabilities absent in rigid-powered MAVs, thus showing the potential of a new class of hybrid soft-rigid robots.

We introduce SplitFlyer-a novel quadcopter with an ability to disassemble into two self-contained bicopters through human assistance. As a subunit, the bicopter is a severely underactuated aerial vehicle equipped with only two propellers. Still, each bicopter is capable of independent flight. To achieve this, we provide an analysis of the system dynamics by relaxing the control over the yaw rotation, allowing the bicopter to maintain its large spinning rate in flight. Taking into account the gyroscopic motion, the dynamics are described and a cascaded control strategy is developed. We constructed a transformable prototype to demonstrate consecutive flights in both configurations. The results verify the proposed control strategy and show the potential of the platform for future research in modular aerial swarm robotics.

This paper addresses the problem of cooperative transport of a point mass hoisted by two aerial robots. Treating the robots as a leader and a follower, the follower stabilizes the system with respect to the leader using only feedback from its Inertial Measurement Units (IMU). This is accomplished by neglecting the acceleration of the leader, analyzing the system through the generalized coordinates or the cables’ angles, and employing an observation model based on the IMU measurements. A lightweight estimator based on an Extended Kalman Filter (EKF) and a controller are derived to stabilize the robot-payload-robot system. The proposed methods are verified with extensive flight experiments, first with a single robot and then with two robots. The results show that the follower is capable of realizing the desired quasi-static trajectory using only its IMU measurements. The outcomes demonstrate promising progress towards the goal of autonomous cooperative transport of a suspended payload via small flying robots with minimal sensing and computational requirements.

In this article, we introduce Universal Flying Objects-a modular aerial robotic platform for transforming a rigid object into a multirotor robot. To achieve this, we develop flight modules, in the form of a control module and propelling modules that can be affixed to an object. The object, or payload, serves as the airframe of the vehicle. The modular design produces a highly versatile platform as it is reconfigurable by the addition or removal of flight modules, adjustment of the modules' arrangement, or change of payloads. To facilitate the flight control, we propose an inertial measurement unit (IMU)-based estimation strategy for rapid computation of the robot's configuration. When combined with the adaptive geometric controller for further refinement of uncertain parameters, stable flights are accomplished with minimal manual intervention or tuning required by a user. To this end, we demonstrate hovering and trajectory tracking flights through various robot configurations with different dummy payloads, weighing ≈200-800 g, using four to eight propelling modules. The results reveal that stable flights are attainable thanks to the proposed IMU-based estimation method. The flight performance is markedly improved over time through the adaptive scheme, with position errors of a few centimeters after the parameter convergence.

Motivated by a winged seed, which takes advantage of a wing with high angles of attack and its associated leading-edge vortex to boost lift, we propose a powered 13.8gram aerial robot with the maximum take-off weight of 310 mN (31.6 gram) or thrust-to-weight ratio of 2.3. The robot, consisting of two airfoils and two horizontally directed motor-driven propellers, revolves around its vertical axis to hover. To amplify the thrust production while retaining a minimal weight, we develop an optimization framework for the robot and airfoil geometries. The analysis integrates quasi-steady aerodynamic models for the airfoils and the propellers with the motor model. We fabricated the robots according to the optimized design. The prototypes are experimentally tested. The revolving-wing robot produces approximately 50% higher lift compared to conventional multirotor designs. Finally, an uncontrolled hovering flight is presented.

At millimeter and centimeter scales, flapping-wing robots often employ flexural passive wing hinges to eliminate extra actuation and mechanical complexity. In this paper, we propose a modified quasi-steady model for predicting aerodynamic forces from a flapping wing with a passively rotating hinge. The model is based on a simplifying assumption of balanced torque (aerodynamic torque equals to the restoring torque from the hinge). The resulting lift and drag can then be accurately predicted by the modified quasi-steady model without direct knowledge of the angle of attack of the wing. Approximate expression of stroke-averaged forces are also derived. We performed flapping experiments on a centimeter-scale device and the measured lifts show good agreement with the model predictions.

Motivated by the potential of bimodal aerial and surface locomotion as an energy saving strategy for small flying robots, we investigate the effects of a flat overhang surface in the vicinity of a spinning propeller. We employ the classical momentum theory and the blade element method to describe the “ceiling effects” in regards to the generated thrust, power, and rotational speed of the propeller in terms of a normalized distance between the ceiling and the propeller. Validating experiments were performed on a benchtop setup, and the results are in agreement with the proposed models. The presence of a ceiling was found to reduce the power consumption by more than a factor of three for the same thrust force. Overall, our findings show promise, paving the way for the use of perching maneuvers by small rotorcraft to extend their missions.

Despite having achieved unconstrained stable flight, the insect-scale flapping-wing robot is still tethered for power and control. Towards the goal of operating a biologically-inspired robot autonomously outside of laboratory conditions. In this paper, we simulate outdoor disturbances in the laboratory setting and investigate the effects of wind gusts on the flight dynamics of a millimeter-scale flapping wing robot. Simplified models describing the disturbance effects on the robot's dynamics are proposed, together with two disturbance rejection schemes capable of estimating and compensating for the disturbances. The proposed methods are experimentally verified. The results show that they reduced the root mean square position errors by approximately 50% when the robot was subject to 60 cm·s-1horizontal wind.

Without sufficient payload capacity to carry necessary electronic components, flying robots at the scale of insects cannot fly autonomously. Using a simple scaling heuristic to determine a few salient vehicle properties, we develop a vehicle design that possesses the requisite payload capacity for the full suite of required components for control autonomy. We construct the vehicle using state-of-the-art methods, producing a 380 mg vehicle with a 115 mg payload capacity, and demonstrate controlled hovering of the fully-loaded vehicle. The payload-capable vehicle demonstrated here establishes a scalable vehicle design and validates current fabrication methods, laying a foundation for an eventual, fully-integrated robotic system.

Inspired by the agility of flying insects and the recent development on an insect-scale aerial vehicle, we propose a single-loop adaptive flight control suite designed with an emphasis on the ability to track dynamic trajectories as a step towards the goal of performing acrobatic maneuvers as observed in real insects. Instead of the conventional approach of having cascaded control loops, the proposed controller directly regulates the commanded torques to stabilize the attitude and lateral position in a single loop. The method is verified by performing trajectory following flights with the insect-like robot. The results show that the position errors during trajectory following flights are comparable to those observed from steady hovering flights.

Experimentally collected flight dynamics data of flapping-wing microrobots reveals several characteristics that cannot be captured by the information gathered from static experiments. For an insect-sized flapping-wing micro air vehicle with air dampers, we show that a physics-based quasi-steady aerodynamic model is able to predict the flight dynamics with reasonable accuracy. The proposed model is optimized for the vehicle of interest through the use of learning algorithms. The identified model demonstrates the potential for future use in control applications.

Challenges for controlled flight of a robotic insect are due to the inherent instability of the system, complex fluid-structure interactions, and the general lack of a complete system model. In this paper, we propose theoretical models of the system based on the limited information available from previous work and a comprehensive adaptive flight controller that is capable of coping with uncertainties in the system. We have demonstrated that the proposed methods enable the robot to achieve sustained hovering flights with relatively small errors compared to a similar but non-adaptive approach. Furthermore, vertical takeoff and landing flights are also shown to illustrate the fidelity of the flight controller.

The Harvard RoboBee is the first insect-scale cflapping-wing robot weighing less than 100 mg that is able to lift its own weight. However, when flown without guide wires, this vehicle quickly tumbles after takeoff because of instability in its dynamics. Here, we show that by adding aerodynamic dampers, we can can alter the vehicle's dynamics to stabilize its upright orientation. We provide an analysis using wind tunnel experiments and a dynamic model. We demonstrate stable vertical takeoff, and using a marker-based external camera tracking system, hovering altitude control in an active feedback loop. These results provide a stable platform for both system dynamics characterization and unconstrained active maneuvers of the vehicle and represent the first known hovering demonstration of an insect-scale flapping-wing robot.