Precisely twisted: Active torsion during the upward wing stroke 4 Lift and propulsion in the one movement: Upward ... Active articulated torsional drive Flapping-wing flight comprises two principal movements. First, the wings beat up and down, whereby a lever mechanism causes the degree of deflection to increase from the torso to the wing tip. Second, the wing twists in such a way that its leading edge is directed upwards during the upward stroke, so that the wing adopts a positive angle of attack. If the rotation were solely due to the wing’s elasticity, passive torsion would result. If on the other hand the sequencing of the torsion and its magnitude are controlled by an actuator, the wing’s torsion is not passive, but active. The wing: Lift and propulsion in birds SmartBird’s wings each consist of a two-part arm wing spar with an axle bearing located on the torso, a trapezoidal joint as is used in enlarged form on industrial excavators, and a hand wing spar. The trapezoidal joint has an amplitude ratio of 1:3. The arm wing generates lift, and the hand wing beyond the trapezoidal joint provides propulsion. Both the spars of the inner and the outer wing are torsionally resistant. The active torsion is achieved by a servomotor at the end of the outer wing which twists the wing against the spar via the outmost rib of the wing. Partially linear kinematics for optimal thrust When SmartBird lifts its wings, the servo motor for active torsion twists the tips of the hand wings to a positive angle of attack, which is then changed to a negative angle a fraction of a wing beat period. The angle of torsion remains constant between these phases. Thanks to this sequence of movements, the airflow along the wing profile can be optimally used to generate thrust. The torso: a secure housing for the technology The battery, engine and transmission, the crank mechanism and the control and regulation electronics are housed in SmartBird’s torso. By means of a two-stage helical transmission, the exterior rotor motor causes the wings to beat up and down with a reduction ratio of 1:45. This motor is fitted with three Hall sensors that pre-
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