There are many challenges to measuring power input and force output from a flapping vertebrate. Animals can vary a multitude of kinematic parameters simultaneously, and methods for measuring power ...and force are either not possible in a flying vertebrate or are very time and equipment intensive. To circumvent these challenges, we constructed a robotic, multi-articulated bat wing that allows us to measure power input and force output simultaneously, across a range of kinematic parameters. The robot is modeled after the lesser dog-faced fruit bat, Cynopterus brachyotis, and contains seven joints powered by three servo motors. Collectively, this joint and motor arrangement allows the robot to vary wingbeat frequency, wingbeat amplitude, stroke plane, downstroke ratio, and wing folding. We describe the design, construction, programing, instrumentation, characterization, and analysis of the robot. We show that the kinematics, inputs, and outputs demonstrate good repeatability both within and among trials. Finally, we describe lessons about the structure of living bats learned from trying to mimic their flight in a robotic wing.
Bird flight is a remarkable adaptation that has allowed the approximately 10 000 extant species to colonize all terrestrial habitats on earth including high elevations, polar regions, distant ...islands, arid deserts, and many others. Birds exhibit numerous physiological and biomechanical adaptations for flight. Although bird flight is often studied at the level of aerodynamics, morphology, wingbeat kinematics, muscle activity, or sensory guidance independently, in reality these systems are naturally integrated. There has been an abundance of new studies in these mechanistic aspects of avian biology but comparatively less recent work on the physiological ecology of avian flight. Here we review research at the interface of the systems used in flight control and discuss several common themes. Modulation of aerodynamic forces to respond to different challenges is driven by three primary mechanisms: wing velocity about the shoulder, shape within the wing, and angle of attack. For birds that flap, the distinction between velocity and shape modulation synthesizes diverse studies in morphology, wing motion, and motor control. Recently developed tools for studying bird flight are influencing multiple areas of investigation, and in particular the role of sensory systems in flight control. How sensory information is transformed into motor commands in the avian brain remains, however, a largely unexplored frontier.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Birds that use high flapping frequencies can modulate aerodynamic force by varying wing velocity, which is primarily a function of stroke amplitude and wingbeat frequency. Previous measurements from ...zebra finches (
) flying across a range of speeds in a wind tunnel demonstrate that although the birds modulated both wingbeat kinematic parameters, they exhibited greater changes in stroke amplitude. These two kinematic parameters contribute equally to aerodynamic force, so the preference for modulating amplitude over frequency may instead derive from limitations of muscle physiology at high frequency. We tested this hypothesis by developing a novel
work loop approach to measure muscle force and power output from the whole pectoralis major of zebra finches. This method allowed for multiple measurements over several hours without significant degradation in muscle power. We explored the parameter space of stimulus, strain amplitude and cycle frequencies measured previously from zebra finches, which revealed overall high net power output of the muscle, despite substantial levels of counter-productive power during muscle lengthening. We directly compared how changes to muscle shortening velocity via strain amplitude and cycle frequency affected muscle power. Increases in strain amplitude led to increased power output during shortening with little to no change in power output during lengthening. In contrast, increases in cycle frequency did not lead to increased power during shortening but instead increased counter-productive power during lengthening. These results demonstrate why at high wingbeat frequency, increasing wing stroke amplitude could be a more effective mechanism to cope with increased aerodynamic demands.
Flying animals of different masses vary widely in body proportions, but the functional implications of this variation are often unclear. We address this ambiguity by developing an integrative ...allometric approach, which we apply here to hummingbirds to examine how the physical environment, wing morphology and stroke kinematics have contributed to the evolution of their highly specialised flight. Surprisingly, hummingbirds maintain constant wing velocity despite an order of magnitude variation in body weight; increased weight is supported solely through disproportionate increases in wing area. Conversely, wing velocity increases with body weight within species, compensating for lower relative wing area in larger individuals. By comparing inter- and intraspecific allometries, we find that the extreme wing area allometry of hummingbirds is likely an adaptation to maintain constant burst flight capacity and induced power requirements with increasing weight. Selection for relatively large wings simultaneously maximises aerial performance and minimises flight costs, which are essential elements of humming bird life history.
Control of wing shape is believed to be a key feature that allows most birds to produce aerodynamically efficient flight behaviors and high maneuverability. Anatomical organization of intrinsic wing ...muscles suggests specific roles for the different motor elements in wing shape modulation, but testing these hypothesized functions requires challenging measurements of muscle activation and strain patterns, and force dynamics. The wing muscles that have been best characterized during flight are the elbow muscles of the pigeon (
).
studies during different flight modes revealed variation in strain profile, activation timing and duration, and contractile cycle frequency of the humerotriceps, suggesting that this muscle may alter wing shape in diverse ways. To examine the multifunction potential of the humerotriceps, we developed an
work loop approach to measure how activation duration and contractile cycle frequency affected muscle work and power across the full range of activation onset times. The humerotriceps produced predominantly net negative power, likely due to relatively long stimulus durations, indicating that it absorbs work, but the work loop shapes also suggest varying degrees of elastic energy storage and release. The humerotriceps consistently exhibited positive and negative instantaneous power within a single contractile cycle, across all treatments. When combined with previous
studies, our results indicate that both within and across contractile cycles, the humerotriceps can dynamically shift among roles of actuator, brake, and stiff or compliant spring, based on activation properties that vary with flight mode.
Bat wings, like other mammalian forelimbs, contain many joints within the digits. These joints collectively affect dynamic three‐dimensional (3D) wing shape, thereby affecting the amount of ...aerodynamic force a wing can generate. Bats are a speciose group, and show substantial variation in the number of wing joints. Additionally, some bat species have joints with extensor but no flexor muscles. While several studies have examined the diversity in number of joints and presence of muscles, musculoskeletal variation in the digits has not been interpreted in phylogenetic, functional or ecological contexts. To provide this context, the number of joints and the presence/absence of muscles are quantified for 44 bat species, and are mapped phylogenetically. It is shown that, relative to the ancestral state, joints and muscles were lost multiple times from different digits and in many lineages. It is also shown that joints lacking flexors undergo cyclical flexion and extension, in a manner similar to that observed in joints with both flexors and extensors. Comparison of species with contrasting feeding ecologies demonstrates that species that feed primarily on non‐mobile food (e.g. fruit) have fewer fully active joints than species that catch mobile prey (e.g. insects). It is hypothesized that there is a functional trade‐off between energetic savings and maneuverability. Having fewer joints and muscles reduces the mass of the wing, thereby reducing the energetic requirements of flapping flight, and having more joints increases the assortment of possible 3D wing shapes, thereby enhancing the range and fine control of aerodynamic force production and thus maneuverability.
Gliding is an efficient form of travel found in every major group of terrestrial vertebrates. Gliding is often modelled in equilibrium, where aerodynamic forces exactly balance body weight resulting ...in constant velocity. Although the equilibrium model is relevant for long-distance gliding, such as soaring by birds, it may not be realistic for shorter distances between trees. To understand the aerodynamics of inter-tree gliding, we used direct observation and mathematical modelling. We used videography (60–125 fps) to track and reconstruct the three-dimensional trajectories of northern flying squirrels (Glaucomys sabrinus) in nature. From their trajectories, we calculated velocities, aerodynamic forces and force coefficients. We determined that flying squirrels do not glide at equilibrium, and instead demonstrate continuously changing velocities, forces and force coefficients, and generate more lift than needed to balance body weight. We compared observed glide performance with mathematical simulations that use constant force coefficients, a characteristic of equilibrium glides. Simulations with varying force coefficients, such as those of live squirrels, demonstrated better whole-glide performance compared with the theoretical equilibrium state. Using results from both the observed glides and the simulation, we describe the mechanics and execution of inter-tree glides, and then discuss how gliding behaviour may relate to the evolution of flapping flight.
Bats display a wide variety of behaviors that require different amounts of aerodynamic force. To control and modulate aerodynamic force, bats change wing kinematics, which, in turn, may change the ...power required for wing motion. There are many kinematic mechanisms that bats, and other flapping animals, can use to increase aerodynamic force, e.g. increasing wingbeat frequency or amplitude. However, we do not know if there is a difference in energetic cost between these different kinematic mechanisms. To assess the relationship between mechanical power input and aerodynamic force output across different isolated kinematic parameters, we programmed a robotic bat wing to flap over a range of kinematic parameters and measured aerodynamic force and mechanical power. We systematically varied five kinematic parameters: wingbeat frequency, wingbeat amplitude, stroke plane angle, downstroke ratio, and wing folding. Kinematic values were based on observed values from free flying Cynopterus brachyotis, the species on which the robot was based. We describe how lift, thrust, and power change with increases in each kinematic variable. We compare the power costs associated with generating additional force through the four kinematic mechanisms controlled at the shoulder, and show that all four mechanisms require approximately the same power to generate a given force. This result suggests that no single parameter offers an energetic advantage over the others. Finally, we show that retracting the wing during upstroke reduces power requirements for flapping and increases net lift production, but decreases net thrust production. These results compare well with studies performed on C. brachyotis, offering insight into natural flight kinematics.
Bats typically roost head-under-heels but they cannot hover in this position, thus, landing on a ceiling presents a biomechanical challenge. To land, a bat must perform an acrobatic flip that brings ...the claws of the toes in contact with the ceiling and do so gently enough as to avoid injury to its slender hindlimbs. In the present study, we sought to determine how bats land, to seek a link between landing kinematics and ceiling impact forces, and to determine whether landing strategies vary among bat species. To do this, we measured the kinematics and kinetics of landing behaviour in three species of bats as they landed on a force-measuring platform (Cynopterus brachyotis, N=3; Carollia perspicillata, N=5; Glossophaga soricina, N=5). Kinematics were similar for all bats within a species but differed among species. C. brachyotis performed four-point landings, during which body pitch increased until the ventral surface of the body faced the ceiling and the thumbs and hindlimbs simultaneously grasped the surface. Bats of the other two species performed two-point landings, whereby only the hindlimbs made contact with the ceiling. During these two-point landings, the hindlimbs were drawn up the side of the body to come in contact with the ceiling, causing simultaneous changes in body pitch, roll and yaw over the course of the landing sequence. Right-handed and left-handed forms of the two-point landing were observed, with individuals often switching back and forth between them among landing events. The four-point landing of C. brachyotis resulted in larger peak forces (3.7+/-2.4 body weights; median +/- interquartile range) than the two-point landings of C. perspicillata (0.8+/-0.6 body weights) or G. soricina (0.8+/-0.2 body weights). Our results demonstrate that the kinematics and kinetics of landing vary among bat species and that there is a correlation between the way a bat moves its body when it lands and the magnitude of peak impact force it experiences during that landing. We postulate that these interspecific differences in impact force could result because of stronger selective pressure for gentle landing in cave-roosting (C. perspicillata, G. soricina) versus foliage-roosting (C. brachyotis) species.
Birds that use high flapping frequencies can modulate aerodynamic force by varying wing velocity, which is primarily a function of stroke amplitude and wingbeat frequency. Previous measurements from ...zebra finches (Taeniopygia guttata) flying across a range of speeds in a wind tunnel demonstrate that although the birds modulated both wingbeat kinematic parameters, they exhibited greater changes in stroke amplitude. These two kinematic parameters contribute equally to aerodynamic force, so the preference for modulating amplitude over frequency may instead derive from limitations of muscle physiology at high frequency. We tested this hypothesis by developing a novel in situ work loop approach to measure muscle force and power output from the whole pectoralis major of zebra finches. This method allowed for multiple measurements over several hours without significant degradation in muscle power. We explored the parameter space of stimulus, strain amplitude and cycle frequencies measured previously from zebra finches, which revealed overall high net power output of the muscle, despite substantial levels of counter-productive power during muscle lengthening. We directly compared how changes to muscle shortening velocity via strain amplitude and cycle frequency affected muscle power. Increases in strain amplitude led to increased power output during shortening with little to no change in power output during lengthening. In contrast, increases in cycle frequency did not lead to increased power during shortening but instead increased counter-productive power during lengthening. These results demonstrate why at high wingbeat frequency, increasing wing stroke amplitude could be a more effective mechanism to cope with increased aerodynamic demands.
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