Sideways crab-walking is faster and more efficient than forward walking for a hexapod robot

Abstract

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.

Underwater legged robotics: review and perspectives

“…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.…”

Get a grip: inward dactyl motions improve efficiency of sideways-walking gait for an amphibious crab-like robot

“…The crab leg's workspace consists of −80 • to 20 • for θ 1 and −130 • to 0 • for θ 2 (figure 2). This range and workspace is the same as defined in [32,43].…”

“…In this paper, we aim to determine the effects of incorporating the DIG strategy into walking gaits for a crab-like robot. Because we have previously demonstrated the benefits of sideways walking rather than forward walking for our crab-like robot, Sebastian (figure 1) [32], we solely focus on sideways gaits. Specifically, we implement two different alternating tripod gaits which differ in their swing path: one which minimizes swing path distance for a desired step height and lifting angle, and the other which alters the former's swing path to incorporate the DIG strategy.…”

Multi-constraint spatial coupling for the body joint quadruped robot and the CPG control method on rough terrain

“…In this process, the robot has to both climb over different obstacles and constantly adjust its position to adapt to the drastic changes of the terrain, and the dynamic change of the robot can cause its center of gravity (COG) to project outside the area of foothold, which can lead to unstable or even overturn [3]. The quadruped robots should have features such as optimized gait planning algorithms [4], high stability margins [5], and sensitive responses to ensure they can efficiently and quickly complete preset tasks in complex or rough terrain environments, where a stable gait is essential [6]. Currently, legged robots are mainly rigid bodies, and the primary research concerns improving their high dynamicity, environmental adaptability, and large load capacity [7][8][9].…”