A distinctive feature of quadrupeds that is integral to their locomotion is the tail. Tails serve many purposes in biological systems including propulsion, counterbalance, and stabilization while walking, running, climbing, or jumping. Similarly, tails in legged robots may augment the stability and maneuverability of legged robots by providing an additional point of contact with the ground. However, in the field of terrestrial bio-inspired legged robotics, the tail is often ignored because of the difficulties in design and control. This study will test the hypothesis that a variable stiffness robotic tail can improve the performance of a sprawling quadruped robot by enhancing its stability and maneuverability in various environments. To test our hypothesis, we add a multi-segment, cable-driven, flexible tail, whose stiffness is controlled by a single servo motor in conjunction with a reel and cable system, to the underactuated sprawling quadruped robot. By controlling the stiffness of the tail, we have shown that the stability of locomotion on rough terrain and the climbing ability of the robot are improved compared to the movement with a rigid tail and no tail. The flexible tail design also provides passively controlled tail undulation capabilities through the robot's lateral movement, which contributes to stability.

翻译：四足动物运动中不可或缺的一个显著特征是尾巴。在生物系统中，尾巴具有多种功能，包括行走、奔跑、攀爬或跳跃时的推进、平衡和稳定。同样，在腿式机器人中，尾巴可通过提供额外的地面接触点来增强其稳定性和机动性。然而，在陆生仿生腿式机器人领域，由于设计和控制的困难，尾巴常常被忽略。本研究将验证一个假设：可变刚度机器人尾巴能够通过增强爬行四足机器人在不同环境中的稳定性和机动性来提升其运动性能。为验证该假设，我们在欠驱动爬行四足机器人上加装了一种多段线驱动柔性尾巴，其刚度由单个伺服电机配合卷轴和线缆系统控制。通过控制尾巴刚度，我们证明，与刚性尾巴和无尾巴运动相比，机器人在崎岖地形上的运动稳定性和攀爬能力均得到提升。柔性尾巴设计还通过机器人侧向运动实现了被动控制的尾巴摆动能力，这有助于提高稳定性。