The overall objective of the BATMAV project is the development of a biologically inspired bat-like Micro-Aerial Vehicle (MAV) with flexible and foldable wings, capable of flapping flight. This first phase of the project focuses particularly on the kinematical analysis of the wing motion in order to build an artificial-muscle-driven actuation system in the future. While flapping flight in MAV has been previously studied and a number of models were realized using light-weight nature-inspired rigid wings, this paper presents a first model for a platform that features bat-inspired wings with a number of flexible joints which allows mimicking the kinematics of the real flyer. The bat was chosen after an extensive analysis of the flight physics of small birds, bats and large insects characterized by superior gust rejection and obstacle avoidance. Typical engineering parameters such as wing loading, wing beat frequency etc. were studied and it was concluded that bats are a suitable platform that can be actuated efficiently using artificial muscles. Also, due to their wing camber variation, they can operate effectively at a large range of speeds and allow remarkably maneuverable flight. In order to understand how to implement the artificial muscles on a bat-like platform, the analysis was followed by a study of bat flight kinematics. Due to their obvious complexity, only a limited number of degrees of freedom (DOF) were selected to characterize the flexible wing's stroke pattern. An extended analysis of flight styles in bats based on the data collected by Norberg [1] and the engineering theory of robotic manipulators resulted in a 2 and 4-DOF models which managed to mimic the wingbeat cycle of the natural flyer. The results of the kinematical model can be used to optimize the lengths and the attachment locations of the wires such that enough lift, thrust and wing stroke are obtained.

Due to the availability of small sensors, Micro-Aerial Vehicles (MAVs) can be used for detection missions of biological, chemical and nuclear agents. Traditionally these devices used fixed or rotary wings, actuated with electric DC motortransmission, a system which brings the disadvantage of a heavier platform. The overall objective of the BATMAV project is to develop a biologically inspired bat-like MAV with flexible and foldable wings for flapping flight. This paper presents a flight platform that features bat-inspired wings which are able to actively fold their elbow joints. A previous analysis of the flight physics for small birds, bats and large insects, revealed that the mammalian flight anatomy represents a suitable flight platform that can be actuated efficiently using Shape Memory Alloy (SMA) artificial-muscles. A previous study of the flight styles in bats based on the data collected by Norberg [1] helped to identify the required joint angles as relevant degrees of freedom for wing actuation. Using the engineering theory of robotic manipulators, engineering kinematic models of wings with 2 and 3-DOFs were designed to mimic the wing trajectories of the natural flier Plecotus auritus. Solid models of the bat-like skeleton were designed based on the linear and angular dimensions resulted from the kinematic models. This structure of the flight platform was fabricated using rapid prototyping technologies and assembled to form a desktop prototype with 2-DOFs wings. Preliminary flapping test showed suitable trajectories for wrist and wingtip that mimic the flapping cycle of the natural flyer.

The main objective of the BATMAV project is the development of a biologically-inspired Micro Aerial Vehicle (MAV) with flexible and foldable wings for flapping flight. While flapping flight in MAV has been previously studied and a number of models were realized they usually had unfoldable wings actuated with DC motors and mechanical transmission to provide the flapping motion, a system that brings the disadvantage of a heavy flight platform. This phase of the BATMAV project presents a flight platform that features bat-inspired wings with a number of flexible joints to allow mimicking the kinematics of the real mammalian flyer. The bat was chosen after an extensive analysis of the flight parameters of small birds, bats and large insects characterized by a superior maneuverability and wind gust rejection. Morphological and aerodynamic parameters were collected from existing literature and compared concluding that bat wing present a suitable platform that can be actuated efficiently using artificial muscles. Due to their wing camber variation, the bat species can operate effectively at a large rage of speeds and allow remarkably maneuverable and agile flight. Bat skeleton measurements were taken and modeled in SolidWorks to accurately reproduce bones and body via rapid prototyping machines. Much attention was paid specifically to achieving the comparable strength, elasticity, and range of motion of a naturally occurring bat. Therefore, a desktop model was designed, fabricated and assembled in order to study and optimize the effect of various flapping patterns on thrust and lift forces. As a whole, the BATMAV project consists of four major stages of development: the current phase — design and fabrication of the skeletal structure of the flight platform, selection and testing different materials for the design of a compliant bat-like membrane, analysis of the kinematics and kinetics of bat flight in order to design a biomechanical muscle system for actuation, and design of the electrical control architecture to coordinate the platform flight.

This paper presents an actuator placement study for a bio-inspired joint that is part of a smart-materials-based bat wing. The wing has been designed as part of the BATMAV project with the final goal of developing a biologically-inspired micro-air vehicle with foldable wings for flapping flight. The wing uses superelastic Shape Memory Alloy (SMA) joints and SMA muscle wire actuation. A kinematic model for the bat's flapping flight motion has been developed in a previous paper, while the current paper presents a study to determine attachment points for SMA actuator wires. At the center of the current analysis is the requirement to maintain compatibility with a typical SMA's strain capabilities while simultaneously ensuring the required joint angle motion to be achieved. The study yields a range of attachment parameters, which result in contraction strains of up to 2.5%, appropriate for high-cycle actuation. MOTIVATIONIn the past decade Micro-Aerial Vehicles (MAV's) have drawn a great interest especially for applications in dangerous environments for sensing of biological agents, chemical compounds, radioactivity of nuclear materials, as well as in confined spaces where maneuverability is necessary such as in internal inspection of pipes, exploration around rubble in collapsed buildings and surveillance of indoor environments or to avoid collision with buildings, trees, hills, etc, since these devices fly at a relatively low altitudes, i.e. less than 300 ft. Traditionally, MAV's were scaled down from military or civil aircraft using either fixed or rotary wings. A DC motor-transmission system is used to propel these vehicles that can carry batteries, cameras, micro-servos for flight control and R/C transmitters. Using smart materials and structures for actuation and for platform design, the BATMAV project introduces a relatively new way to reduce the weight of the aircraft. Some of the advantages that the SMA actuation has over the traditional DC motor actuation include an extremely light weight, highest work output from a significantly less complex linear actuator and the ability to replicate the flight muscle-tendons of the bat wing. Furthermore, the SMA actuation presents a superelastic characteristic to resist on plastic deformation and fatigue. INTRODUCTIONIn order to improve the maneuverability and aerodynamic performance, engineers started to look into nature for inspiration and designed MAVs for flapping flight. An example is the bio-inspired battery-powered Microbat for flapping flight developed by Sirirak et al [2], having light-MEMS wings with a membrane and wireframe fabricated from parylene C and titanium-alloy. The wings of the Microbat do not actively change shape, however. They change shape passively due to inertial and aerodynamic forces. The wings flap simply in a vertical plane to produce thrust and lift. Another example is the 50g mechanical insect called Entomopter of Michelson [3] from Georgia Tech. that uses a Reciprocating Chemical Muscle to actuate four wings for flapping flight. Its wings ...

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The overall objective of the BATMAV project is the development of a biologically-inspired Micro Aerial Vehicle (MAV) with flexible and foldable wings for flapping flight. This paper presents a platform that features bat-inspired wings which are able to mimic the folding motion of the elbow and wrist joints of the natural flyer. This flapping platform makes use of the dual roll of the Shape Memory Alloys (SMA) to mimic the flexible joints and flapping muscles of the natural wings. The approach of this project was to learn from the natural flyer through a systematic analysis of their flight and to mimic their flapping mechanisms. A systematic study of the bat flight kinematics helped to identify the required joint angles as relevant degrees of freedom for wing actuation. Kinematic models of wings with 2 and 3-DOFs have been developed with the intention of mimicking the wing trajectories of the natural flier Plecotus auritus. A further kinematic model for the joint rotation angle has been developed in order to determine the attachment locations of SMA ‘muscle-wires’ as well as their routes along the wing ‘bones’. As part of this study individual elbow-joint systems were designed, fabricated and used to experimentally validate the above model’s prediction. The elastic skin membrane of the bat wing has been reproduced using a thin-film silicon membrane which has been suitably prestrained and shaped to mimic the leading and trailing edges of the bat wing. To measure the aerodynamic forces developed by the flapping platform, a test stand consisting of two load cells was assembled, and the dynamic tests were performed for a 2-DOF flapping wings. The lift and thrust forces as well as the flapping amplitude were measured.