Dactyls and inward gripping stance for amphibious crab-like robots on sand

Abstract

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.

Hands to Hexapods, Wearable User Interface Design for Specifying Leg Placement for Legged Robots

“…The goal of our glove is to relate motions of a common hexapod leg to finger motions. A common robot leg design has three joints ( Graf et al, 2019 , 2021 ; Wooden et al, 2010 ; Boston Dynamics, 2022 ; Michael, 2012 ; Hwangbo et al, 2019 ; Darling, 2015 ; Sartoretti et al, 2018 ; Coelho et al, 2021 ), as shown in Figure 3 : a hip joint with vertical axis of rotation, a knee joint, and an ankle joint with parallel axes of rotation. Just like one robot leg has three joints, there are three joints on one finger: the metacarpophalangeal joint (MCP), the proximal interphalangeal joint (PIP) and the distal interphalangeal joint (DIP) ( Jones and Lederman, 2006 ; Palastanga and Soames, 2011 ; Wheatland et al, 2015 ).…”

“… Hexapod robots (left) and human hands (right) have similarities that can be convenient for user interfaces. For example, a user might want to use a single finger to lift a single leg of this crab-like hexapod ( Bjelonic et al, 2016 ; Franchi et al, 2012 ; Carpentier and Mansard, 2018 ; Grezmak et al, 2021 ; Graf et al, 2019 ; Graf et al, 2021 ). …”

“…This is novel compared to current methods for controlling hexapod robots. For hexapod robots ( Bjelonic et al, 2016 ; Franchi et al, 2012 ; Carpentier and Mansard, 2018 ; Grezmak et al, 2021 ; Graf et al, 2019 ; Graf et al, 2021 ), a simple control interface like joystick or arrows on a keyboard ( Kurisu, 2011 ) is easy and intuitive for the operator to control the locomotion velocity, direction, attitude or even step size, as pictured in Figure 2A . However, both these control interfaces can only control the robot to do pre-programmed motions.…”

Shape Memory Alloy‐Based Soft Amphibious Robot Capable of Seal‐Inspired Locomotion

“…[ 1,2 ] There have been many other amphibious robot designs inspired by gait‐changing animals. [ 3–12 ] However, most were built of rigid components that make the interaction of the robots with the environment unwieldy. On the other hand, soft robots based on smart materials and compliant structures have displayed great potential in complying with varying terrain and unplanned situations.…”

“…On the other hand, soft robots based on smart materials and compliant structures have displayed great potential in complying with varying terrain and unplanned situations. [13][14][15][16][17][18][19][20][21][22][23][24][25][26] Therefore, the development of soft amphibious robots based on different soft actuation principles was naturally carried out [4,8,[25][26][27] and was found to be successful in navigating multimodal environments. Among the different soft actuation principles explored, various soft-body movements with shape memory alloy (SMA) wires have been achieved at a compact scale, including jumping, [17] crawling, [15,28,29] peristaltic, [30,31] swimming [32] , and even rolling [14] .…”