Generation of Inverted Locomotion Gait for Multi-Legged Robots Using a Spherical Magnet Joint and Adjustable Sleeve

In this paper, we propose a design and an implementation of spherical magnet joint (SMJ) - based gait generation for inverted locomotion of multi-legged robots. A spherical permanent magnet is selected to generate a consistent attractive force for the robot to perform inverted locomotion under steel structures. Additionally, the tip of the robot's foot is designed as a ball-joint mechanism to give flexibility to the foot placement at any angle between the tip and surfaces. We also propose an adjustable sleeve mechanism to detach the tip of the foot during locomotion by creating a fulcrum point during the tilt and pull step. As a result, the reaction force can be reduced according to sleeve diameter. Experimental results show that the presented load decreased by 46% from direct pulling with the adjustable sleeve mechanism. For inverted locomotion, a quadruped robot and a hexapod robot were constructed to represent the predominant type of multi-legged robot. We integrated the SMJ and the adjustable sleeve on both robots and performed the inverted locomotion with a crawling gait, a trotting gait, a square gait, and a tripod gait. Our analysis demonstrates the characteristics of each gait in terms of velocity, stability, guaranteeing the versatility of our proposed SMJ, which can be applied to different types of legged robots.

Power Consumption Characteristics Research on Mobile System of Electrically Driven Large-Load-Ratio Six-Legged Robot

To research the power consumption characteristics of mobile system of an electrically driven large-load-ratio six-legged robot with engineering capability is beneficial to speed up it toward practicability. Based on the configuration and walking modes of robot, the mathematical model of the power consumption of mobile system is set up. In view of the tripod gait is often selected for the six-legged robots, the simplified power consumption model of mobile system under the tripod gait is established by means of reducing the dimension of the robot's statically indeterminate problem and constructing the equal force distribution. Then, the power consumption of robot mobile system is solved under different working conditions. The variable tendencies of the power consumption of robot mobile system are respectively obtained with changes in the rotational angles of hip joint and knee joint, body height, and span. The articulated rotational zones and the ranges of body height and span are determined under the lowest power consumption. According to the walking experiments of prototype, the variable tendencies of the average power consumption of robot mobile system are respectively acquired with changes in the duty ratio, body height, and span. Then, the feasibility and correctness of theory analysis are verified in the power consumption of robot mobile system. The proposed analysis method in this paper can provide a reference on the lower power research of the large-load-ratio multi-legged robots.

Gait Design and Analysis of Quadruped Crawling Robot Climbing Over the Raised Terrain of Slope

Background: It is a challenge that quadruped crawling robots face when working in the raised terrain of slope. The robot is affected by gravity and gait under this terrain, the ground reaction force on its hind legs is relatively large. This has strict requirements for the structure and gait planning of the quadruped crawling robot. Objective: Aiming at that the ground reaction force on the hind legs of quadruped crawling robot is relatively large when the robot climbing over the raised terrain of slope, a slope-triangular gait walking strategy for quadruped robots based on a layered CGP gait generation method is proposed. Methods: Three-dimensional model of the quadruped crawling robot is created in SOLIDWORKS. The kinematic model is established, and the foot position vector is obtained. Consider the characteristics of the raised terrain of slope, slope tripod gait and hierarchical CPG slope tripod gait generator are proposed. Comparative simulation of sloped tripod gait and flat tripod gait, the slope tripod gait with and without the gait generator is carried out by Adams programming. Results: Compared the centroid displacement curve, foot speed curve, and foot contact force curve of slope tripod gait and flat tripod gait. Compare the posture angle curves of the fuselage with and without the slope tripod gait generator. The result proves that the tripod gait walking strategy is feasible. Conclusion: The slope tripod gait walking strategy can improve the impact resistance of the quadruped crawling robot on sloped high ground. The gait design and motion analysis process of the robot can provide a reference for other quadruped crawling robot device.v

Descending and Ascending Signals That Maintain Rhythmic Walking Pattern in Crickets

The cricket is one of the model animals used to investigate the neuronal mechanisms underlying adaptive locomotion. An intact cricket walks mostly with a tripod gait, similar to other insects. The motor control center of the leg movements is located in the thoracic ganglia. In this study, we investigated the walking gait patterns of the crickets whose ventral nerve cords were surgically cut to gain an understanding of how the descending signals from the head ganglia and ascending signals from the abdominal nervous system into the thoracic ganglia mediate the initiation and coordination of the walking gait pattern. Crickets whose paired connectives between the brain and subesophageal ganglion (SEG) (circumesophageal connectives) were cut exhibited a tripod gait pattern. However, when one side of the circumesophageal connectives was cut, the crickets continued to turn in the opposite direction to the connective cut. Crickets whose paired connectives between the SEG and prothoracic ganglion were cut did not walk, whereas the crickets exhibited an ordinal tripod gait pattern when one side of the connectives was intact. Crickets whose paired connectives between the metathoracic ganglion and abdominal ganglia were cut initiated walking, although the gait was not a coordinated tripod pattern, whereas the crickets exhibited a tripod gait when one side of the connectives was intact. These results suggest that the brain plays an inhibitory role in initiating leg movements and that both the descending signals from the head ganglia and the ascending signals from the abdominal nervous system are important in initiating and coordinating insect walking gait patterns.

Drosophila uses a tripod gait across all walking speeds, and the geometry of the tripod is important for speed control

Changes in walking speed are characterized by changes in both the animal’s gait and the mechanics of its interaction with the ground. Here we study these changes in walking Drosophila. We measured the fly’s center of mass movement with high spatial resolution and the position of its footprints. Flies predominantly employ a modified tripod gait that only changes marginally with speed. The mechanics of a tripod gait can be approximated with a simple model – angular and radial spring-loaded inverted pendulum (ARSLIP) – which is characterized by two springs of an effective leg that become stiffer as the speed increases. Surprisingly, the change in the stiffness of the spring is mediated by the change in tripod shape rather than a change in stiffness of individual legs. The effect of tripod shape on mechanics can also explain the large variation in kinematics among insects, and ARSLIP can model these variations.

Leg amputation modifies coordinated activation of the middle leg muscles in the cricket Gryllus bimaculatus

Insects alter their walking pattern in order to respond to demands of an ever-changing environment, such as varying ground surface textures. They also exhibit resilient and flexible ability to retain the capacity to walk even after substantial changes in their body properties, e.g. leg amputation. While the motor control paradigm governing the inter-leg coordination in such adaptive walking has been extensively described in past studies, the mechanism remains unknown. Here, we examined this question by using the cricket (Gryllus bimaculatus), which shows a tetrapod/tripod gait on a flat surfaces, like many other insects. We performed leg amputation experiments to investigate modifications of leg movements and coordination of muscle activities. We simultaneously recorded (1) the leg movements, locomotion velocity, and body rotation and (2) the leg movements and leg muscles activities before and after leg amputation. Crickets displayed adaptive coordination of leg movement patterns in response to amputations. The activation timings of levator muscles in both middle legs tended to synchronize in phase when both legs were amputated at the coxatrochanteral joint. This supports the hypothesis that an intrinsic contralateral connection within the mesothoracic ganglion exists, and that mechanosensory feedback from the legs override this connection, resulting in the anti-phase movement of a normal gait.

Hybrid Gait Planning of A Hexapod Robot

The adapotation of gaits pattern is a basic and important for the hexapod robot to move stably and efficiently, which depends on the servos of the robot’s legs, and also the body structure of the robot.This paper compares the tripod gait and the crab-inspired gait for a specific hexapod to move forward and move backward; turn left and turn right and integrates the two gaits to apply them under different conditions. The hexapod has three servos on each legs, thus the freedom level of each leg is three-degree. From the comparative experiment, this two gait patterns are suitable for different turning demands.

Descending and ascending signals that maintain rhythmic walking pattern in the cricket

The cricket is one of the model animals used to investigate the neuronal mechanisms underlying adaptive locomotion. An intact cricket walks with a tripod gait, similar to other insects. The motor control center of the leg movements is located in the thoracic ganglia. In this study, we investigated the walking gait patterns of crickets whose ventral nerve cords were surgically cut to gain an understanding of how the descending signals from the head ganglia and ascending signals from the abdominal nervous system into the thoracic ganglia mediate the initiation and coordination of the walking gait pattern. Crickets whose paired connectives between the brain and subesophageal ganglion (SEG) were cut exhibited a tripod gait pattern. However, when one side of the connectives between the brain and SEG was cut, the crickets continued to turn in the opposite direction to the connective cut. Crickets whose paired connectives between the SEG and prothoracic ganglion were cut did not walk, whereas the crickets exhibited an ordinal tripod gait pattern when one side of the connectives was intact. Crickets whose paired connectives between the metathoracic ganglion and abdominal ganglia were cut initiated walking, although the gait was not a coordinated tripod pattern, whereas the crickets exhibited a tripod gait when one side of the connectives was intact. These results suggest that the brain plays an inhibitory role in initiating leg movements, and that both the descending signals from the head ganglia and the ascending signals from the abdominal nervous system are both important in initiating and coordinating insect walking gait patterns.