Bo Cheng

• PhD
• Professor (Associate) at Pennsylvania State University

Flying animals resort to fast, large-degree-of-freedom motion of flapping wings, a key feature that distinguishes them from rotary or fixed-winged robotic fliers with limited motion of aerodynamic surfaces. However, flapping-wing aerodynamics are characterized by highly unsteady and three-dimensional flows difficult to model or control, and accurat...

Inverted landing in a rapid and robust manner is a challenging feat for aerial robots, especially while depending entirely on onboard sensing and computation. In spite of this, this feat is routinely performed by biological fliers such as bats, flies, and bees. Our previous work has identified a direct causal connection between a series of onboard...

Hummingbirds have evolved to hover and manoeuvre with exceptional flight control. This is enabled by their musculoskeletal system that successfully exploits the agile motion of flapping wings. Here, we synthesize existing empirical and modelling data to generate novel hypotheses for principles of hummingbird wing actuation. These may help guide fut...

Fish locomotion emerges from diverse interactions among deformable structures, surrounding fluids and neuromuscular activations, i.e. fluid–structure interactions (FSI) controlled by fish's motor systems. Previous studies suggested that such motor-controlled FSI may possess embodied traits. However, their implications in motor learning, neuromuscul...

Hummingbirds routinely execute a variety of stunning aerobatic feats, which continue to challenge current notions of aerial agility and controlled stability in biological systems. Indeed, the control of these amazing manoeuvres is not well understood. Here, we examined how hummingbirds control a sequence of manoeuvres within milliseconds, and teste...

Perching significantly enhances the energy efficiency and operational versatility of aerial robots. This article introduces a passive and tunable perching mechanism designed for smooth surfaces. The design features a bistable mechanism (BM) with a soft suction cup, augmented by two sets of shape memory alloy (SMA) actuators for active tuning. The B...

Natural fliers with flapping wings face the dual challenges of energy efficiency and active control of wing motion for achieving diverse modes of flight. It is hypothesized that flapping-wing systems use resonance to improve muscle mechanical output energy efficiency, a principle often followed in bioinspired flapping-wing robots. However, resonanc...

One of the most ancient and evolutionarily conserved behaviors in the animal kingdom involves utilizing wind-borne odor plumes to track essential elements such as food, mates, and predators. Insects, particularly flies, demonstrate a remarkable proficiency in this behavior, efficiently processing complex odor information encompassing concentrations...

Fish use their lateral lines to sense flows and pressure gradients, enabling them to detect nearby objects and organisms. Towards replicating this capability, we demonstrated successful leader-follower formation swimming using flow pressure sensing in our undulatory robotic fish ($\mu$Bot/MUBot). The follower $\mu$Bot is equipped at its head with b...

Inverted landing is a routine behavior among a number of animal fliers. However, mastering this feat poses a considerable challenge for robotic fliers, especially to perform dynamic perching with rapid body rotations (or flips) and landing against gravity. Inverted landing in flies have suggested that optical flow senses are closely linked to the p...

This work demonstrates universal dynamic perching capabilities for quadrotors of various sizes and on surfaces with different orientations. By employing a non-dimensionalization framework and deep reinforcement learning, we systematically assessed how robot size and surface orientation affect landing capabilities. We hypothesized that maintaining g...

When a hovering hummingbird performs a rapid escape manoeuvre in response to a perceived threat from the front side, its body may go through simultaneous pitch, yaw and roll rotations. In this study, we examined the inertial coupling of the three-axis body rotations and its effect on the flight mechanics of the manoeuvre using analyses of high-spee...

Insect wings are flexible structures that exhibit deformations of complex spatiotemporal patterns. Existing studies on wing deformation underscore the indispensable role of wing deformation in enhancing aerodynamic performance. Here, we investigated forward flight in bluebottle flies, flying semi-freely in a magnetic flight mill; we quantified wing...

In animal and robot swimmers of body and caudal fin (BCF) form, hydrodynamic thrust is mainly produced by their caudal fins, the stiffness of which has profound effects on both thrust and efficiency of swimming. Caudal fin stiffness also affects the motor control and resulting swimming gaits that correspond to optimal swimming performance; however,...

In this work, we explored a bioinspired method for underwater object sensing based on active proprioception. We investigated whether the fluid flows generated by a robotic flapper, while interacting with an underwater wall, can encode the distance information between the wall and the flapper, and how to decode this information using the propriocept...

Inspired by the stability achieved by biological flapping-winged fliers in gusty environments, we conducted particle image velocimetry studies on the interactions between plunging wings and large-scale vortex gusts. Our experiments involved a flat plate wing performing sinusoidal plunging motions at various frequencies, resulting in Strouhal number...

Hummingbird flight is the epitome of extreme aerial agility and controlled stability, as hummingbirds routinely exercise a variety of stunning aerobatic feats. Yet, the control of these amazing maneuvers is not well understood. Here we examined how hummingbirds control a sequence of maneuvers within milliseconds and tested whether and when their vi...

Hummingbirds outperform other birds in terms of aerial agility at low flight speeds. To reveal the key mechanisms that enable such unparalleled agility, we reconstructed body and wing motion of hummingbird escape manoeuvres from high-speed videos; then, we performed computational fluid dynamics modelling and flight mechanics analysis, in which the...

The leading-edge vortex (LEV) is well known for its contribution to the high-lift generation in a wide variety of biological organisms, such as flying insects, auto-rotating samaras, and gliding snakes. Based on revolving wings, the temporal–spatial evolution of the LEV, including the fundamental vorticity dynamics and stabilizing mechanisms, is re...

Previous studies suggested that wing pitching, i.e. the wing rotation around its long axis, of insects and hummingbirds is primarily driven by an inertial effect associated with stroke deceleration and acceleration of the wings and is thus passive. Here we considered the rapid escape maneuver of hummingbirds who were initially hovering but then sta...

Hummingbirds outperform other birds in terms of aerial agility at low flight speeds. To reveal the key mechanisms that enable such unparalleled agility, we reconstructed body and wing motion of hummingbird escape maneuvers from high-speed videos; then, we performed computational fluid dynamics modeling and flight mechanics analysis, in which each w...

Fish locomotion emerges from a diversity of interactions among deformable structures, surrounding fluids and neuromuscular activations, i.e., fluid-structure interactions (FSI) controlled by fish's motor systems. Previous studies suggested that such motor-controlled FSI may possess embodied traits. However, their implications in motor learning, neu...

The physics of leading-edge vortex (LEV) stability on flapping wings and autorotating seeds is still underexplored due to its complex dependency on Reynolds number ( $\textit {Re}$ ), aspect ratio ( AR ) and Rossby number ( Ro ). Our previous study observed an interesting dual-stage vortex tilting between radial and tangential components in a stabl...

Physical injury often impairs mobility, which can have dire consequences for survival in animals. Revealing mechanisms of robust biological intelligence to prevent system failure can provide critical insights into how complex brains generate adaptive movement and inspiration to design fault-tolerant robots. For flying animals, physical injury to a...

Hummingbirds have evolved to hover and maneuver with exceptional flight control. This is directly enabled by their musculoskeletal system that successfully exploits the agile motion of flapping wings. Here, we reveal novel principles of hummingbird wing actuation that provide insights into the evolution and robotic emulation of hummingbird flight....

The mechanisms of leading-edge vortex (LEV) formation and its stable attachment to revolving wings depend highly on Reynolds number ( $\textit {Re}$ ). In this study, using numerical methods, we examined the $\textit {Re}$ dependence of LEV formation dynamics and stability on revolving wings with $\textit {Re}$ ranging from 10 to 5000. Our results...

In this work we developed a mathematical model and a simulation platform for a fish-inspired robotic template, namely Magnetic, Modular, Undulatory Robotics (µBots). Through this platform, we systematically explored the effects of design and fluid parameters on the swimming performance via reinforcement learning. The mathematical model was composed...

In this work we developed a mathematical model and a simulation platform for a fish-inspired robotic template, namely Magnetic, Modular, Undulatory Robotics ($\mu$Bots). Through this platform, we systematically explored the effects of design and fluid parameters on the swimming performance via reinforcement learning. The mathematical model was comp...

Inverted landing is a challenging feat to perform in aerial robots, especially without external positioning. However, it is routinely performed by biological fliers such as bees, flies, and bats. Our previous observations of landing behaviors in flies suggest an open-loop causal relationship between their putative visual cues and the kinematics of...

Here we developed an experimental platform with a magnetic, modular, undulatory robot (µBot) for studying fish-inspired underwater locomotion. This platform will enable us to systematically explore the relationship between body morphology, swimming gaits, and swimming performance via reinforcement learning methods. The µBot was designed to be easil...

Flying animals resort to fast, large-degree-of-freedom motion of flapping wings (i.e., their aerodynamic surfaces), a key feature that distinguishes them from rotary or fixed-winged robotic fliers with relatively limited motion of aerodynamic surfaces. However, it is well known that flapping-wing aerodynamics are characterised by highly unsteady an...

In revolving or flapping wings, radial planetary vorticity tilting (PVTr) is a mechanism that contributes to the removal of radial (spanwise) vorticity within the leading-edge vortex (LEV), while vorticity advection increases its strength. Dimensional analysis predicts that the PVTr and advection should scale with the wing aspect-ratio (AR) in iden...

This is the Supplementary Material B regarding the geometric-similarity, global averaging, nonlinear regressions and the statistical analysis.

This is the Supplementary Material A regarding the identification of the quasi-steady period.

Micro aerial vehicles (MAV) with multiple rotors, or multicopters, have many promising applications ranging from environmental monitoring, agricultural inspection, to package delivery. These applications, however, usually face a critical problem: the flight time of MAVs is limited due to the low aerodynamic efficiency and high energy consumption. O...

Bioinspired Structures and Design - edited by Wole Soboyejo September 2020

Landing upside down on a ceiling is challenging as it requires a flier to invert its body and land against the gravity, a process that demands a stringent spatiotemporal coordination of body translational and rotational motion. Although such an aerobatic feat is routinely performed by biological fliers such as flies, it is not yet achieved in aeria...

Cambridge Core - Materials Science - Bioinspired Structures and Design - edited by Wole Soboyejo

In the presence of wind or background image motion, flies are able to maintain a constant retinal slip velocity via regulating flight speed to the extent permitted by their locomotor capacity. Here we investigated the retinal slip compensation of tethered blue-bottle flies (Calliphora vomitoria) flying semi-freely along an annular corridor in a mag...

The wake structures generated by rotating wings are studied numerically to investigate the complex vortex formation and evolution in both near-wake and far-wake regions. Flat rectangular wings with finite aspect ratios (AR = 1–8) that rotate from rest at an angle of attack ranging from 15° to 90° in a low Reynolds number regime (200–1600) are consi...

Both the transient formation and the stable attachment of leading-edge vortex (LEV) contribute to the high lift generation of an insect wing when it revolves at high angles of attack. In this study, we examined the LEV formation and the transient lift generation on a revolving wing with Reynolds number at 1500 and aspect ratio at 3, using combined...

Within the leading-edge vortex (LEV) of a revolving wing, planetary vorticity tilting (PVTr) can partly remove the radial vorticity generated by advection, a mechanism that relates the effects of Coriolis acceleration, spanwise flow, and the tilting of the planetary vorticity. It has been shown previously that the non-dimensional PVTr scales indepe...

Flies and other insects routinely land upside down on a ceiling. These inverted landing maneuvers are among the most remarkable aerobatic feats, yet the full range of these behaviors and their underlying sensorimotor processes remain largely unknown. Here, we report that successful inverted landing in flies involves a serial sequence of well-coordi...

Flies regulate speed to maintain a constant retinal-image velocity primarily by adjusting their body pitch, despite they can change speed via only the wing motion modulation. To determine whether and to what extent this behavior holds under a fixed body pitch condition, we investigated the speed regulation of semi-tethered blue-bottle flies ( Calli...

Previous studies suggested that Coriolis acceleration and spanwise flow both played key roles in stabilizing the leading-edge vortex (LEV) in revolving wings. The current study examined a mechanism that relates the effects of Coriolis acceleration, spanwise flow, and the tilting of the planetary vorticity on removing the radial component of LEV vor...

In this work, we present an application of a policy gradient algorithm to a real-time robotic learning problem, where the goal is to maximize the average lift generation of a dynamically scaled robotic wing at a constant Reynolds number (Re). Compared to our previous work, the merit of this work is twofold. First, a central pattern generator (CPG)...

Thrust generation is a crucial aspect of fish locomotion that depends on a variety of morphological and kinematic parameters. In this work, the kinematics of caudal fin motion of a robotic fish are optimised experimentally. The robotic fish actuates its caudal fin with flapping and rotation motion, and also measures the fin hydrodynamic force and t...

Flies fly at a broad range of speeds and produce sophisticated aerial maneuvers with precisely controlled wing movements. Remarkably, only subtle changes in wing motion are used by flies to produce aerial maneuvers, resulting in little directional tilt of the aerodynamic force vector relative to the body. Therefore, it is often considered that flie...

Leading-edge vortex (LEV) is a hallmark of insect flight that forms and remains stably attached on high angle-of-attack (AoA), low aspect ratio (AR) wings undergoing revolving or flapping motion. Despite the efforts on explaining the stability of LEV when it reaches steady state in revolving wings, its formation process remains largely underexplore...

Many biological organisms (e.g. insects, birds, and mammals) rely on the perception of an informational variable called time-to-contact (TTC) to control their motion for various tasks such as avoiding obstacles, landing, or interception. TTC, defined as the required time to contact an object if the current velocity is maintained, has been recently...

This paper uses optimal periodic control (OPC) theory as a framework for assessing the relative efficiency of revolving versus flapping wing trajectories in insect-sized flight problems. The literature already offers both experimental and simulation-based comparisons between these two flight modes. A collective conclusion from these studies is that...

This work investigated the vorticity dynamics and stability of leading-edge vortices (LEVs) in revolving wings. Previous studies suggested that Coriolis acceleration and spanwise flow both played key roles in stabilizing the LEV; however, the exact mechanism remains unclear. The current study examined a mechanism that relates the effects of Corioli...

Flies fly at a broad range of speeds and produce sophisticated aerial maneuvers with precisely controlled wing movements. Remarkably, only subtle changes in wing motion are used by flies to produce aerial maneuvers, resulting in little directional tilt of aerodynamic force vector relative to the body. Therefore, it is often considered that flies fl...

In this work, we present a successful application of a policy search algorithm to a real-time robotic learning problem, where the goal is to maximize the efficiency of lift generation on a dynamically scaled flapping robotic wing. The robotic wing has two degrees-of-freedom, i.e., stroke and pitch, and operates in a tank filled with mineral oil. Fo...

In this work, a multi-objective optimization framework is developed for optimizing low Reynolds number () hovering flight. This framework is then applied to compare the efficiency of rigid revolving and flapping wings with rectangular shape under varying and Rossby number (, or aspect ratio). The proposed framework is capable of generating sets of...

Due to adverse viscous effects, revolving wings suffer universally from low efficiency at low Reynolds number (Re). By reciprocating wing revolving motion, natural flyers flying at low Re successfully exploit unsteady effects to augment force production and efficiency. Here we investigate the aerodynamics of an alternative, i.e., a revolving wing w...

Flap-bounding, a form of intermittent flight, is often exhibited by small birds over their entire range of flight speeds. Its purpose is unclear during low to medium speed (2 m·s⁻¹–8 m·s⁻¹) flight: aerodynamic models suggest continuous flapping would require less power output and lower cost of transport. To explore its functional significance at lo...

At low Reynolds numbers, revolving wings become less efficient in generating lift for hovering flight due to the increasing adverse viscous effects. Flying insects use reciprocating revolving wings that exploit unsteady aerodynamic mechanisms for lift augmentation. Here, the aerodynamics of an alternative that introduces unsteadiness to the revolvi...

Submitted for the DFD 2017 Meeting of The American Physical Society Sorting Category: 2.2 (E)

This work investigates the radial vorticity dynamics and the stability of leading-edge vortices (LEVs) in revolving wings. Previous studies have shown that Coriolis acceleration plays a key role in stabilizing the LEV; however, the exact mechanism remains unclear. This study tests a new hypothesis based on the curl of the Coriolis acceleration in t...

Flying animals ranging in size from fruit flies to hummingbirds are nimble fliers with remarkable rotational manoeuvrability. The degrees of manoeuvrability among these animals, however, are noticeably diverse and do not simply follow scaling rules of flight dynamics or muscle power capacity. As all manoeuvres emerge from the complex interactions o...

Insect flight has gained wide interests in both biology and engineering communities in the past decades regarding its aerodynamics, sensing and flight control. However, studying insect flight experimentally remains a challenge in both free-flight and tethered-flight settings. In free flight experiments, due to highly unpredictable and fast flight b...

The superior manoeuvrability of hummingbirds emerges from complex interactions of specialized neural and physiological processes with the unique flight dynamics of flapping wings. Escape manoeuvring is an ecologically relevant, natural behaviour of hummingbirds, from which we can gain understanding into the functional limits of vertebrate locomotor...

Hummingbirds are nature's masters of aerobatic manoeuvres. Previous research shows hummingbirds and insects converged evolutionarily upon similar aerodynamic mechanisms and kinematics in hovering. Herein, we use three-dimensional kinematic data to begin to test for similar convergence of kinematics used for escape flight and to explore the effects...

The superior maneuverability of insect flight is enabled by rapid and significant changes in aerodynamic forces, a result of subtle and precise change of wing kinematics. The high sensitivity of aerodynamic force to wing kinematic change demands precise and instantaneous feedback control of the wing motion trajectory, especially in the presence of...

The prominent maneuverability of flapping flight is enabled by rapid and significant changes in aerodynamic forces, which is a result of surprisingly subtle and precise changes of wing kinematics. The high sensitivity of aerodynamic forces to wing kinematic changes demands precise and instantaneous control of the flapping wing trajectories, especia...

We conducted a systematic experimental study to investigate the aerodynamic effects of active trailing-edge flexion on a high aspect ratio wing translating from rest at a high angle of attack (AoA). We varied the timing and speed of the trailing-edge flexion, and measured the resulting aerodynamic effects using a combination of direct force measure...

An electromagnetic actuator weighing 2.6 grams and operated at resonance is presented with the intended application to flapping wing MAV’s. Comprised of a single electromagnetic coil, a permanent magnet rotor, and a “virtual spring” magnet pair, system resonance is achieved using a periodic excitation voltage applied to the coil, resulting in harmo...

Insects are able to create complex wing trajectories using power and steering muscles attached to the wing/thorax oscillation system. In this paper, we propose a dynamic model for such an oscillation system, and study its dynamic behavior. In particular, we model the wing as a rigid body with three degrees of freedom. The power muscle is modeled by...

Flapping wings continuously create and send vortices into their wake, while imparting downward momentum into the surrounding fluid. However, experimental studies concerning the details of the three-dimensional vorticity distribution and evolution in the far wake are limited. In this study, the three-dimensional vortex wake structure in both the nea...

The flapping wings of flying animals create complex vortex wake structure; understanding its spatial and temporal distribution is fundamental to animal flight theory. In this study, we applied the volumetric 3-component velocimetry to capture both the near- and far-field flow generated by a pair of mechanical flapping wings. For the first time, the...

Graphical abstract