Jindrich DL, Full RJ
Department of Integrative Biology, University of California at Berkeley, Berkeley, CA 94720, USA.
J Exp Biol. 1999 Jun;202 (Pt 12):1603-23. doi: 10.1242/jeb.202.12.1603.
Remarkable similarities in the vertical plane of forward motion exist among diverse legged runners. The effect of differences in posture may be reflected instead in maneuverability occurring in the horizontal plane. The maneuver we selected was turning during rapid running by the cockroach Blaberus discoidalis, a sprawled-postured arthropod. Executing a turn successfully involves at least two requirements. The animal's mean heading (the direction of the mean velocity vector of the center of mass) must be deflected, and the animal's body must rotate to keep the body axis aligned with the heading. We used two-dimensional kinematics to estimate net forces and rotational torques, and a photoelastic technique to estimate single-leg ground-reaction forces during turning. Stride frequencies and duty factors did not differ among legs during turning. The inside legs ended their steps closer to the body than during straight-ahead running, suggesting that they contributed to turning the body. However, the inside legs did not contribute forces or torques to turning the body, but actively pushed against the turn. Legs farther from the center of rotation on the outside of the turn contributed the majority of force and torque impulse which caused the body to turn. The dynamics of turning could not be predicted from kinematic measurements alone. To interpret the single-leg forces observed during turning, we have developed a general model that relates leg force production and leg position to turning performance. The model predicts that all legs could turn the body. Front legs can contribute most effectively to turning by producing forces nearly perpendicular to the heading, whereas middle and hind legs must produce additional force parallel to the heading. The force production necessary to turn required only minor alterations in the force hexapods generate during dynamically stable, straight-ahead locomotion. A consideration of maneuverability in the horizontal plane revealed that a sprawled-postured, hexapodal body design may provide exceptional performance with simplified control.
在各种有腿的奔跑者中,向前运动的垂直平面存在显著的相似性。姿势差异的影响可能反而体现在水平面的机动性上。我们选择的动作是在快速奔跑过程中由蜚蠊(一种姿势伸展的节肢动物)进行转弯。成功完成转弯至少涉及两个要求。动物的平均航向(质心平均速度矢量的方向)必须偏转,并且动物的身体必须旋转以保持身体轴线与航向对齐。我们使用二维运动学来估计净力和旋转扭矩,并使用光弹性技术来估计转弯过程中单腿的地面反作用力。转弯过程中各腿的步频和 duty 因子没有差异。内侧腿在转弯时比直线奔跑时更靠近身体结束步幅,这表明它们有助于身体转弯。然而,内侧腿并没有为身体转弯提供力或扭矩,而是积极地抵抗转弯。转弯外侧离旋转中心较远的腿贡献了导致身体转弯的大部分力和扭矩冲量。仅从运动学测量无法预测转弯的动力学。为了解释转弯过程中观察到的单腿力,我们开发了一个通用模型,该模型将腿部力的产生和腿部位置与转弯性能联系起来。该模型预测所有腿都可以使身体转弯。前腿通过产生几乎垂直于航向的力可以最有效地为转弯做出贡献,而中腿和后腿必须产生平行于航向的额外力。转弯所需的力的产生只需要在动态稳定的直线运动过程中六足动物产生的力上进行微小的改变。对水平面机动性的考虑表明,一种姿势伸展的六足身体设计可能通过简化控制提供卓越的性能。