BATMAV: Development and Testing of a SMA-Based Bio-Inspired Flapping Platform

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.