Sandy beaches are areas that challenge robots of all sizes, especially smaller scale robots. Sand can hinder locomotion and waves apply hydrodynamic forces which can displace, reorient, or even invert the robot. Crab-like legs and gaits are well suited for this environment and could be used as inspiration for an improved design of robots operating in this terrain. Tapered, curved feet (similar to crab dactyl shape) paired with a distributed inward gripping method are hypothesized to enable better anchoring in sand to resist hydrodynamic forces. This work demonstrates that crab-like legs can withstand vertical forces that are larger than the body weight (e.g. in submerged sand, the force required to lift the robot can be up to 138% of the robot weight). Such legs help the robot hold its place against hydrodynamic forces imparted by waves (e.g. compared to displacement of 42.7 mm with the original feet, crab-like feet reduced displacement to 1.6 mm in lab wave tests). These feet are compatible with walking on sandy and rocky terrain (tested at three speeds: slow, medium, and fast), albeit at reduced speeds from traditional feet. This work shows potential for future robots to utilize tapered and curved feet to traverse challenging surf zone terrain where biological crabs thrive.
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), robots that can walk forward or sideways often pick a direction by convention. In this paper, we compare walking in forward and sideways directions. To do this, a simple gait design method is introduced for determining forward and sideways gaits with equivalent body heights and step heights. Specifically, the frequency and stride lengths are tuned within reasonable constraints to find gaits that represent a robot’s performance potential in terms of speed and energy cost. Experiments are performed in both dynamic simulation in Webots and a laboratory environment with our 18 degree-of-freedom (DOF) hexapod robot, Sebastian. With the common three joint leg design, the results show that sideways walking is overall better (75% larger walking speed and 40% lower COT). The performance of sideways walking was better on both hard floors and granular media (dry play sand). This supports the development of future crab-like walking robots for future applications. In future work, this approach may be used to develop nominal gaits without extensive optimization, and to explore whether the advantages of sideways walking persist for other hexapod designs.
Crabs are adept at traversing natural terrains that are challenging for mobile robots. Curved dactyls are a characteristic feature to engage terrain for resisting wave forces in surf zones. Inward gripping motions at the onset of stance could increase stability.Here, we add inward gripping motions to the foot trajectories of walking gaits to determine the energetic costs and speed for our 12 DOF crab-like robot, Sebastian. Specifically, we compared two gaits in which the step size (stance length) was the same, but the swing trajectories were either triangular (to minimize trajectory length) or quadrilateral (in which the leg deliberately oversteps in order to perform a distributed inward grip (DIG). The resulting gripping quadrilateral gait significantly outperformed the non-gripping triangular gait on diverse terrains (hard linoleum, soft mats, and underwater sand), providing between 15% and 34% energy savings. Using this gait eliminates the advantage of spherical end effectors for slip reduction on hard linoleum, which may lead to a better understanding of how to use crab-like morphology for more efficient locomotion. Finally, we subjected the walking robot to lab-generated waves with wave height approximately 166% of the dactyl length. Both gaits enabled the robot to walk undisturbed by the waves. Taken together, these results suggest that impact trajectory will be key for future amphibious robots. Future work can provide deeper understanding of the relationships between dactyls, gaits, and substrates in biology and robots.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.