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In both forward (a) and sideways (b) walking, the stance trajectory is a straight line (green) and the swing trajectory is a parabola with height Hs = 6 cm.
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Articulated legs enable the selection of robot gaits, including walking in different directions such as forward or sideways. For longer distances, the best gaits might maximize velocity or minimize the cost of transport (COT). Interestingly, while animals often adapt their morphology for walking either forward (like insects) or sideways (like crabs...
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... robot's dactyls intentionally point inward [30,31] and are therefore not reversible. As shown in figure 4(a), the rotational range for hip joints θ 1 is (−22.5 • , 22.5 • ) and for knee joints θ 2 (−80 • , 20 • ), and for ankle joints θ 3 (−130 • , 0). The negative value for θ 1 is the clockwise direction, and the negative values for θ 2 and θ 3 are the downward direction. ...
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... both forward walking and sideways walking, the stance phase trajectory is a straight line and the swing phase trajectory is a parabola with 6 cm swing height, as in figure 4. We choose 6 cm as the swing height, because this is sufficient for extracting dactyls from the sand. ...
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... about 55% of the trajectory error sideways walking is in the swing phase, so we expect increasing the swing height to decrease speed. Figure 4(a) is the trajectory for the right middle leg for forward walking and figure 4(b) is the trajectory for the right legs' sideways walking. ...
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... stance, the trajectory, figure 4, is defined by endpoints A and B, which are determined by the full stride in figures 3(b) and (c). We divide the stride into k equal segments of equal time. ...
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... forward walking swing phase, the hip angle (θ 1 ) increases at a constant rate and we use inverse kinematics to determine the knee and ankle angles (θ 2 and θ 3 ) that keep the end effector on the desired parabolic trajectory, figure 4. Thus the k + 1 points are determined by increments of (θ 1B − θ 1A )/k, where θ 1B and θ 1A are the θ 1 for point B and A respectively, figure 4. In sideways walking swing phase, the x direction speed is held constant and thus the k + 1 points are determined by increments of (x B − x A )/k, where x B and x A are the x positions for points B and A respectively, figure 4. ...
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... forward walking swing phase, the hip angle (θ 1 ) increases at a constant rate and we use inverse kinematics to determine the knee and ankle angles (θ 2 and θ 3 ) that keep the end effector on the desired parabolic trajectory, figure 4. Thus the k + 1 points are determined by increments of (θ 1B − θ 1A )/k, where θ 1B and θ 1A are the θ 1 for point B and A respectively, figure 4. In sideways walking swing phase, the x direction speed is held constant and thus the k + 1 points are determined by increments of (x B − x A )/k, where x B and x A are the x positions for points B and A respectively, figure 4. ...
Citations
... During the stance motion, the middle leg pulls the robot forward, with the dactyl orientation moving through an pre-determined angle range. In previous work, we describe this angle as the angle between the ground and dactyl (AGD) [38]. At the end of the stance, the dactyl will be pointed further away from the direction of travel, and the weight of the robot pushes the dactyl inwards toward the center of the robot. ...
Shallow underwater environments around the world are contaminated with unexploded ordnances (UXOs). Current state-of-the-art methods for UXO detection and localization use remote sensing systems. Furthermore, human divers are often tasked with confirming UXO existence and retrieval which poses health and safety hazards. In this paper, we describe the application of a crab robot with leg-embedded Hall effect-based sensors to detect and distinguish between UXOs and non-magnetic objects partially buried in sand. The sensors consist of Hall-effect magnetometers and permanent magnets embedded in load bearing compliant segments. The magnetometers are sensitive to magnetic objects in close proximity to the legs and their movement relative to embedded magnets, allowing for both proximity and force-related feedback in dynamically obtained measurements. A dataset of three-axis measurements is collected as the robot steps near and over different UXOs and UXO-like objects, and a convolutional neural network is trained on time domain inputs and evaluated by 5-fold cross validation. Additionally, we propose a novel method for interpreting the importance of measurements in the time domain for the trained classifier. The results demonstrate the potential for accurate and efficient UXO and non-UXO discrimination in the field.
... Chen et al. conducted a comprehensive study on the gait of a hexapod walking robot, comparing forward and lateral walking modes. Their findings revealed superior performance in lateral walking, with a 75% increase in walking speed and a 40% reduction in the coefficient of tangential force [7]. Luneckas et al. introduced an energy-efficient approach for hexapod walking robots, dynamically switching gaits based on the robot's current speed to minimize energy consumption [8,9]. ...
Mars exploration significantly advances our understanding of planetary evolution, the origin of life, and possibilities for Earth’s future. It also holds potential for discovering new mineral resources, energy sources, and potential settlement sites. Navigating Mars’ complex environment and unknown terrain is a formidable challenge, particularly for autonomous exploration. The hexapod walking robot, inspired by ant morphology, emerges as a robust solution. This design offers diverse gait options, mechanical redundancy, high fault tolerance, and stability, rendering it well suited for Martian terrain. This paper details the development of an ant-inspired hexapod robot, emphasizing its terrain adaptability on Mars. A novel terrain detection method utilizing a convolutional neural network enables efficient identification of varied terrain types through semantic segmentation of visual images. Additionally, we introduce a comprehensive motion performance evaluation index for the hexapod robot, including speed and stability. These metrics facilitate effective performance assessment in different environments. A key innovation is the proposed gait switching method for the hexapod robot. This approach allows seamless transition between gaits while in motion, enhancing the robot's ability to traverse challenging terrains. The experimental results validate the effectiveness of this method. Utilizing gait switching leads to a significant improvement in robot performance and stability—58.5% and 41.4% better than using tripod and amble gaits, respectively. Compared to single tripod, amble, and wave gaits, the comprehensive motion performance indices of the robot improved by 36.3%, 30.6%, and 41.1%, respectively. This study can provide new ideas and methods for the motion evaluation and adaptive gait switching of multilegged robots in complex terrains. It significantly enhances the mobility and adaptability of such robots in challenging environments, contributing valuable knowledge to the field of planetary exploration robotics.
... Blake, R. experimentally discussed the effect of flow velocity on the lift-to-drag ratio of crab shells [20]. Through prototype tests, Chen, Y. et al. demonstrated that a crab-type multipedal robot performed better transverse walking than forward walking [21]. Kinugasa, T. et al. discussed that the leg movements of living creatures are highly dependent on the body involved in the dynamics and biological characteristics [22]. ...
Underwater bionic-legged robots encounter significant challenges in attitude, velocity, and positional control due to lift and drag in water current environments, making it difficult to balance operational efficiency with motion stability. This study delves into the hydrodynamic properties of a bionic crab robot’s shell, drawing inspiration from the sea crab’s motion postures. It further refines the robot’s underwater locomotion strategy based on these insights. Initially, the research involved collecting attitude data from crabs during underwater movement through biological observation. Subsequently, hydrodynamic simulations and experimental validations of the bionic shell were conducted, examining the impact of attitude parameters on hydrodynamic performance. The findings reveal that the transverse angle predominantly influences lift and drag. Experiments in a test pool with a crab-like robot, altering transverse angles, demonstrated that increased transverse angles enhance the robot’s underwater walking efficiency, stability, and overall performance.
... Using a hexapod robot, Chen et al. simulated insect-like forward walking and crab-like lateral walking morphology. Crab-like lateral walking performed better on hard surfaces and dry sand [19]. Graf et al. improved the robot's grip on the beach by designing the crab leg joint with a tapered bent leg at the tip of the foot, based on their study of the behavioral characteristic that crabs bend their toes when resisting wave forces in the surf zone [20]. ...
Bionic-legged robots draw inspiration from animal locomotion methods and structures, demonstrating the potential to traverse irregular and unstructured environments. The ability of Portunus trituberculatus (Portunus) to run flexibly and quickly in amphibious environments inspires the design of systems and locomotion methods for amphibious robots. This research describes an amphibious crab-like robot based on Portunus and designs a parallel leg mechanism for the robot based on biological observations. The research creates the group and sequential gait commonly used in multiped robots combined with the form of the robot’s leg mechanism arrangement. This research designed the parallel leg mechanism and modeled its dynamics. Utilizing the outcomes of the dynamics modeling, we calculate the force and torque exerted on each joint of the leg mechanism during group gait and sequential gait when the robot is moving with a load. This analysis aims to assess the performance of the robot’s motion. Finally, a series of performance evaluation experiments are conducted on land and underwater, which show that the amphibious crab-like robot has good walking performance. The crab-like robot can perform forward, backward, left, and right walking well using group and sequential gaits. Simultaneously, the crab-like robot showcases faster movement in group gaits and a more substantial load capacity in sequential gaits.
... Even so, our TLRB experiment still achieved a grasping (moving) distance of 102 mm, which is at least 1.5 times that of the distance achieved by the TLB gait (63 mm). Next, we consider factors affecting the energy consumption of the actuators and analyze gait movement performance using the cost of transport (COT) [33] index, which is defined as follows: ...
Brachiation robots mimic the locomotion of bio-primates, including continuous brachiation and ricochetal brachiation. The hand-eye coordination involved in ricochetal brachiation is complex. Few studies have integrated both continuous and ricochetal brachiation within the same robot. This study seeks to fill this gap. The proposed design mimics the transverse movements of sports climbers holding onto horizontal wall ledges. We analyzed the cause-and-effect relationship among the phases of a single locomotion cycle. This led us to apply a parallel four-link posture constraint in model-based simulation. To facilitate smooth coordination and efficient energy accumulation, we derived the required phase switching conditions as well as joint motion trajectories. Based on a two-hand-release design, we propose a new style of transverse ricochetal brachiation. This design better exploits inertial energy storage for enhanced moving distance. Experiments demonstrate the effectiveness of the proposed design. A simple evaluation method based on the final robot posture from the previous locomotion cycle is applied to predict the success of subsequent locomotion cycles. This evaluation method serves as a valuable reference for future research.
... The category of ULRs is very heterogeneous in terms of morphology and size. Prototypes with one [70,71], two [75], four [68,72,89], six [24,84,102,103,107,108], and eight legs [87] were developed, and legs with one [99], two [71,92], three [24,72,109], or more [110] DoFs were employed. Naturally, ULRs with a higher number of DoFs are potentially more versatile and several behaviours can be implemented on the same robot. ...
... ULRs featuring several DoFs can employ several types of gaits to adapt to different situations. In [107], using the hexapod Sebastian, the differences in terms of speed and cost of transport between sideways and forward walking was investigated, finding that sideways walking is faster and more efficient than forward walking for both hard floors and granular media. The developers of Hexaterra, investigated static gaits to maintain stability on irregular terrains [96], while the developers of SILVER2 proposed an inspection strategy in which the ULR switches from punting to static locomotion upon the detection of a target to approach it safely. ...
Nowadays, there is a growing awareness on the social and economic importance of the ocean. In this context, being able to carry out a diverse range of operations underwater is of paramount importance for many industrial sectors as well as for marine science and to enforce restoration and mitigation actions. Underwater robots allowed us to venture deeper and for longer time into the remote and hostile marine environment. However, traditional design concepts such as propeller driven Remotely Operated Vehicles (ROVs), Autonomous Underwater Vehicles (AUVs), or tracked benthic crawlers, present intrinsic limitations, especially when a close interaction with the environment is required. An increasing number of researchers are proposing legged robots as a bioinspired alternative to traditional designs, capable of yielding versatile multi-terrain locomotion, high stability, and low environmental disturbance. In this work, we aim at presenting the new field of underwater legged robotics in an organic way, discussing the prototypes in the state-of-the-art and highlighting technological and scientific challenges for the future. First, we will briefly recap the latest developments in traditional underwater robotics from which several technological solutions can be adapted, and on which the benchmarking of this new field should be set. Second, we will the retrace the evolution of terrestrial legged robotics, pinpointing the main achievements of the field. Third, we will report a complete state of the art on Underwater Legged Robots (ULRs) focusing on the innovations with respect to the interaction with the environment, sensing and actuation, modelling and control, and autonomy and navigation. Finally, we will thoroughly discuss the reviewed literature by comparing traditional and legged underwater robots, highlighting interesting research opportunities, and presenting use case scenarios derived from marine science applications.
... Therefore, Portunus widely exists in the shoal, surge, and other environments [27]. Many researchers in the field of robotics have already studied crabs and developed a variety of crab robots [9,[28][29][30]. We have learned one kind of the walking gait of Portunus and demonstrated its viability in the amphibious environment with a simple robotic platform [31]. ...
Bionic amphibious robots are the intersection of biology and robotics; they have the advantages of environmental adaptability and maneuverability. An amphibious robot that combines walking and swimming move modes inspired by a crab (Portunus) is presented in this article. The outstanding characteristic of the robot is that its environmental adaptability relies on the bionic multi-modal movement, which is based on two modular bionic swimming legs and six modular walking legs. We designed the biomimetic crab robot based on the biological observation results. The design, analysis, and simulation of its structure and motion parameters are introduced in this paper. The swimming propulsion capability and the walking performance are verified through indoor, pool, and seaside experiments. In conclusion, the designed bionic crab robot provides a platform with practical application capabilities in amphibious environment detection, concealed reconnaissance, and aquaculture.
... The planar motion of these limbs resembles that of simple robotic limbs and therefore may inform effective design principles [37]. Since sideways walking has also been shown to enable faster walking for both biological crabs and crab-inspired robots [27,33], sideways-walking crabs provide valuable inspiration for legged robotics on uneven terrain. ...
... Our intent is to provide a simple, theoretical discussion of how limb geometry influences the ability to step across hemispherical obstacles, and to confirm this geometry in animals who face relevant Our goal is to explore how to use legs with two coplanar joints with horizontal axes of rotation to traverse terrain with regular valley features. These optimizations will be relevant for many robots, including Ghost [23], ANYmal [9], and our crab-like robot Sebastian [27]. The blue and red legs in robots correspond to the same colored limbs in the biological crab. ...
... We envision a gait in which multiple stance legs work together to create opposing forces for stabilization, which can be accomplished by moving either one leg at a time for stability or moving more legs in phase, for example in an alternating tripod gait. This work does not address the control or trajectory planning for the limbs to find the valleys, but other work suggests that this is possible either passively [27,38] or with vision [8,39]. Instead, we are answering the question: how does the ratio of distal to proximal length of a two-jointed leg influence the ability to reach over hemispherical obstacles of varying sizes and produce sufficient traction for force closure and successful walking? ...
Natural terrain is uneven and walking over these substrates may benefit from grasping into the depressions or "valleys" between obstacles. To examine how leg geometry influences walking across obstacles with valleys, we (1) modeled the performance of a two-linkage leg with parallel axis "hip" and "knee" joints to determine how relative segment lengths influence stepping across rocks of varying diameter and (2) measured the walking limbs in two species of intertidal crabs, \textit{Hemigrapsus nudus} and \textit{Pachygrapsus crassipes}, which live on rocky shores and granular terrains. We idealized uneven terrains as adjacent rigid hemispherical "rocks" with valleys between them and calculated kinematic factors such as workspace, limb angles with respect to the ground, and body configurations needed to step rocks. We first find that the simulated foot tip radius relative to the rock radius is limited by friction and material failure. To enable force closure for grasping and assuming that friction coefficients above 0.5 are unrealistic, the foot tip radius must be at least 10 times smaller than that of the rocks. However, ratios above 15 are at risk of fracture. Second, we find the theoretical optimal leg geometry for robots is with the distal segment 0.63 of the total length, which enables traversal of rocks with a diameter 37\% of the total leg length. Surprisingly, the intertidal crabs' walking limbs cluster around the same limb ratio of 0.63, showing deviations for limbs less specialized for walking. Our results can be applied broadly when designing segment lengths and foot shapes for legged robots on uneven terrain, as demonstrated here using a hexapod crab-inspired robot. Furthermore, these findings can inform our understanding of the evolutionary patterns in leg anatomy associated with adapting to rocky terrain.
Quadruped robots have frequently appeared in various situations, including wilderness rescue, planetary exploration, and nuclear power facility maintenance. The quadruped robot with an active body joint has better environmental adaptability than one without body joints. However, it is difficult to guarantee the stability of the body joint quadruped robot when walking on rough terrain. Given the above issues, this paper proposed a gait control method for the body joint quadruped robot based on multi-constraint spatial coupling (MCSC) algorithm. The body workspace of the robot is divided into three subspaces, which are solved for different gaits, and then coupled to obtain the stable workspace of the body. A multi-layer central pattern generator (CPG) model based on the Hopf oscillator is built to realize the generation and switching of walk and trot gaits. Then, combined with the MCSC area of the body, the reflex adjustment strategy on different terrains is established to adjust the body’s posture in real time and realize the robot's stable locomotion. Finally, the robot prototype is developed to verify the effectiveness of the control method. The simulation and experiment results show that the proposed method can reduce the offset of the swing legs and the fluctuation of the body attitude angle. Furthermore, the quadruped robot is ensured to maintain stability by dynamically modifying its body posture. The relevant result can offer a helpful reference for the control of quadruped robots in complex environments.
