A wing mechanism was designed to reproduce a complex accelerative flapping gait from a single constant RPM motor. The flapping gate was deciphered from data obtained by Tobalske and Dial, 1996, of black-billed magpies. The synthesis process begins by specifying a 4R spatial serial chain that resembles a magpie’s anatomy. Moving the spatial chain through the desired flapping gait defines a function of joint angle over time at each of the four joints. A six-bar Stephenson II function generator was designed for each joint angle function and the whole system was coupled together such that it can be run by a motor spinning at constant RPM.
Finally, compliant joints were added between the wrist and wing tip to mimic this portion of a bird’s anatomy. This joints utilize hard stops in order to limit their compliance to one direction creating aerodynamic check values such that control surfaces remain rigid during downstroke and deflect during backstroke.
The resulting motion has a long, stretched out downstroke followed by a quick, compressed backstroke.
B. W. Tobalske and K. P. Dial, “Flight Kinematics of Black-billed Magpies and Pigeons Over A Wide Range of Speeds,” The Journal of Experimental Biology, 199(2): 263-280, 1996.