Quadrupeds exhibit remarkable locomotion performance through the coordination between their limbs and torso. From past biological knowledge, it is understood that during walking, the forelimbs primarily contribute to braking, while the hindlimb are responsible for propulsion. However, in the field of quadruped robot dynamics, effectively leveraging this coordination remains a challenge. To investigate the torso-limb coordination, this study explores the walking performance of a quadruped walker with a compliant torso, driven by the forelimb or the hindlimb. Through numerical simulations, we analyze the walking behavior under different control drive methods. The findings provide insights into the design of compliant-bodied robots and the optimal distribution of propulsion forces between the forelimbs and hindlimbs.

Quadrupedal locomotion involves coordinated interaction between limbs and torso, enabling them to achieve remarkable movement performance and adapt effectively to various environments. In previous studies, mathematical dynamic models of quadrupeds have been established to investigate the mechanisms of limb-torso interaction during walking. However, due to the strong nonlinearity within the model, analyzing how the torso’s motion, especially vibrations, affects walking remains a significant challenge. In this study, the linearization and frequency analysis methods are applied to the quadruped walker to analyze its vibration characteristics, including natural frequency and vibration amplitude. Subsequently, numerical simulations are conducted to examine the relationship between torso vibration and walking performance. Furthermore, a comparison between the vibration characteristics and the simulation results reveals a potential resonance phenomenon. This finding not only validates the effectiveness of the linearization approach but also offers new insights into the interaction between the limbs and torso.

In the natural world, benefited from the advantages of the spine, quadrupeds exhibiting extraordinary flexibility which allowing them to move efficiently on variable terrains. The previous researches have indicated the legged robots which efficiently utilizing their spine can achieve rapid and stable locomotion. However, within the field of legged robot dynamics, the design of the spine and understanding how it positively influences locomotion is unclear, which is significant for quadruped robot to achieve efficient and stable walking. In this study, we proposed a model formed by tensegrity spine and rimless wheel to represent quadrupeds, using passive dynamic walking as a method, which has been well-demonstrated for observing the inherent characteristics, exhibited the locomotion characteristic of the model proposed. By numerical simulation, we observed change trend of locomotion performance with the configurations of spine’s shape, and found direction of spine design that have a positive impact on walking. These findings contribute to the design of spine structures in quadruped robots.

The quadrupeds have wider active territory than humans. Their bodies can adapt various environments through evolution, enabling the efficient, elegant gait for their legged locomotion. Previous researches have indicated lots of examples of utilizing the advantages of body to achieve environment adaptive and stable gait, and for legged locomotion, especially with quadruped robot determining how to generate environment-adaptive mobile locomotion remains a significant challenge. In this study, we discussed the adaptability to environments of quadruped robots, specific walking stability and gait convergence in low-friction environments with compliant torso. The numerically simulations are proposed for observing the trend of walking performance with various friction coefficient. By analyzing the typical walking gait, the adaptability of quadruped walkers with compliant torso are found. These conclusions contribute to the design and development of compliant torso for quadruped walkers.

Magnetically actuated miniature robots are limited in their mechanical outputting capability, because the magnetic forces decrease significantly with decreasing robot size and increasing actuating distance. Hence, the output force of these robots can hardly meet the demand for specific biomedical applications (e.g., tissue penetration). This article proposes a tetherless magnetic impact needle robot (MINRob) based on a triple-magnet system with reversible and repeatable magnetic collisions to overcome this constraint on output force. The working procedure of the proposed system is divided into several states, and a mathematical model is developed to predict and optimize the force output. These force values in magnetic impact and penetration are obtained from a customized setup, indicating a ten-fold increase compared with existing miniature robots that only utilize magnetic attractive force. Eventually, the proposed MINRob is integrated with a teleoperation system, enabling remote and precise control of the robot's position and orientation. The triple-magnet system offers promising locomotion patterns and penetration capacity via the notably increased force output, showing great potential in robot-assisted tissue penetration in minimally invasive healthcare.

This paper proposes novel passive-dynamic walk-ers formed by two cross-shaped frames and eight viscoelastic elements. Since it is a combination of two four-legged rimless wheels via viscoelastic elements, we call it viscoelastically-combined rimless wheel (VCRW). Two types of VCRWs consisting of different cross-shaped frames are introduced; one is formed by combining two Greek-cross-shaped frames (VCRW1), and the other is formed by combining two-link cross-shaped frames that can rotate freely around the central axis (VCRW2). First, we describe the model assumptions and equations of motion and collision. Second, we numerically analyze the basic gait properties of passive dynamic walking. Furthermore, we consider an activation of VCRW2 for gen-erating a stable level gait, and discuss the significance of the study as a novel walking support device.