  Biologically-inspired robots are a very interesting and difficult branch of
robotics dues to its very rich dynamical and morphological complexities. Among
them, flying animals, such as bats, have been among the most difficult to take
inspiration from as they exhibit complex wing articulation. We attempt to
capture several of the key degrees-of-freedom that are present in the natural
flapping gait of a bat. In this work, we present the mechanical design and
analysis of our flapping wing robot, the Aerobat, where we capture the plunging
and flexion-extension in the bat's flapping modes. This robot utilizes gears,
cranks, and four-bar linkage mechanisms to actuate the arm-wing structure
composed of rigid and flexible components monolithically fabricated using
PolyJet 3D printing. The resulting robot exhibits wing expansion and retraction
during the downstroke and upstroke respectively which minimizes the negative
lift and results in a more efficient flapping gait.
