How does a woodpecker work? An impact dynamics approach
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To understand how a woodpecker is able accelerate its head to such a high velocity in a short amount of time, a multi-rigid-segment model of a woodpecker’s body is established in this study. Based on the skeletal specimen of the woodpecker and several videos of woodpeckers pecking, the parameters of a three-degree-of-freedom system are determined. The high velocity of the head is found to be the result of a whipping effect, which could be affected by muscle torque and tendon stiffness. The mechanism of whipping is analyzed by comparing the response of a hinged rod to that of a rigid rod. Depending on the parameters, the dynamic behavior of a hinged rod is classified into three response modes. Of these, a high free-end velocity could be achieved in mode II. The model is then generalized to a multihinge condition, and the free-end velocity is found to increase with hinge number, which explains the high free-end velocity resulting from whipping. Furthermore, the effects of some other factors, such as damping and mass distribution, on the velocity are also discussed.
KeywordsWoodpecker Muscle torque High impact velocity Whipping Hinged rod
The authors gratefully acknowledge the support of the National Natural Science Foundation of China (NSFC) (Grant 11372163) and the National Fundamental Research Program of China (Grant 2011CB610305). The third author (T.X. Yu) gratefully acknowledges the support of the NSFC Key Project 11032001.
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