https://www.mdpi.com/2218-6581/3/2/181/pdf

Design Issues for Hexapod Walking Robots

The objective of this paper is to present the evolution and the state-of-the-art in the area of legged locomotion systems. In a first phase different possibilities for implementing mobile robots are discussed, namely the case of artificial legged locomotion systems, while emphasizing their advantages and limitations. In a second phase a historical overview of the evolution of these systems is presented, bearing in mind several particular cases often considered as milestones of technological and scientific progress. After this historical timeline, some of the present-day systems are examined and their performance is analyzed. In a third phase the major areas of research and development that are presently being followed in the construction of legged robots are pointed out. Finally, some still unsolved problems that remain defying robotics research, are also addressed.

/pdf/a-historical-perspective-of-legged-robots-27p66nhkqy.pdf

A Historical Perspective of Legged Robots

Mobility analysis of the typical gait of a radial symmetrical six-legged robot

In this paper, distribution of required forces and moments to the supporting legs of a six-legged robot is handled as a torque-distribution problem. This approach is comparatively contrasted to the conventional approach of tip-point force distribution. The formulation of dynamics is performed by using the joint torques as the primary variables. The sum of the squares of the joint torques on the supporting legs is considered to be proportional to the dissipated power. The objective function is constructed as this sum, and the problem is formulated as to minimize this quadratic objective function with respect to linear equality and inequality constraints. It is demonstrated that the torque-distribution scheme results in a much more efficient distribution compared with the conventional scheme of force distribution. In contrast to the force distribution, the torque-distribution scheme makes good use of interaction forces and friction in order to minimize the required joint torques

Torque Distribution in a Six-Legged Robot

Multi-legged robots display significant advantages with respect to wheeled ones for walking over rough terrain because they do not need continuous contact with the ground. In Multi-legged robots, hexapod robots, mechanical vehicles that walk on six legs, have attracted considerable attention in recent decades. There are several benefits for hexapods rover. (a) Hexapod robot is easy to maintain static stability on three or more legs, (b) It has a great deal of flexibility in how it can move. (c) Hexapod robot is the most efficient one for statically stable walking. Preumount et al. 1991, observed that a larger number of legs more than six do not increase walking speed. (d) Hexapod robots show robustness in case of leg faults (e) Hexapods makes it possible for the robot to use one, two or three legs to work as hand and perform complex operations. The most studied problem for multi-legged robots concerns how to determine the best sequence for lifting off and placing the feet (gait/locomotion planning). From the stability point of view, robot locomotion can be classified into dynamic locomotion, such as running and hopping, and statically stable locomotion as walking. Statically stable locomotion has the constraint that the moving body is stable at all times. The vertical projection of the centre of gravity of the robot must be within the convex of the supporting polygon linked positions of all supporting feet. Statically stable gait is solely dependent on the design of bodies and legs. Hexapod gaits have been widely investigated as a function of shape and characteristics of the robot structure. In 1985, Kaneko et al. addressed the gait of a rectangular hexapod with decoupled freedoms where the propelling motion was generated by one degree of freedom (DOF). In 1988, Lee et al. realized an omnidirectional walking control system for a rectangular hexapod robot with adaptive suspension. A circular gait was studied for a layered hexapod robot (called Ambler) at the Carnegie Mellon University [Bares et al., 1989; Krotkov & Bares, 1991; Wettergreen, 1990] with rotating legs connected to the same vertical axis at six different heights. Hirose et al. in 1992 and 1998 and Gurocak in 1998 developed other two hexapods whose bodies were consisting of two different layers, each connected to three legs. The relative motion of the layers realized the omnidirectional robot gait in a simple way, but limiting the walking capability under leg faults. Two Lees in 2001 studied the gait of a special robot whose body was composed of three parts connected by revolute joints. Its 18

/pdf/locomotion-analysis-of-hexapod-robot-4sm0gv21iz.pdf

Locomotion Analysis of Hexapod Robot

This paper describes a successful attempt to have Mechanical Engineering and Electrical Engineering final year students working together on a mechatronics project. The work consisted of constructing a prototype six leg walking machine on which arbitrary gaits could be implemented and tested. This vehicle was also used to conduct some basic studies on terrain adaptive gaits and pit avoidance strategies. The test machine consists of a 38 cm long, 1.3 kg rectangular hexapod. Each leg has two degrees of freedom, actuated by position controlled servomotors, and a contact switch in the foot. The electromechanical part was first constructed and interfaced with a PC, via an umbilical. Later, a on-board microcontroller (Intel 8096) was installed, to make the vehicle semi-autonomous. In order to emphasize the influence of the gait on the vehicle behaviour, the paper begins with a review of the stability properties of some well known regular symmetric gaits on flat ground. This work is part of a EEC sponsored TELEMAN project aiming at developing a legged inspection vehicle for disordered, hostile environment. >

Gait analysis and implementation of a six leg walking machine

A conceptual walking vehicle for planetary exploration

The paper reviews the main strategies for the leg co-ordination of a six-legged walking machine. A “free gait” algorithm is presented which allows a smooth and stable motion for an arbitrary velocity vector of the vehicle, including a rotation about the vertical axis. It consists of a rule-based central decision process, based on the analysis of a six component vector called ‘leg phase state’ The co-ordination strategy consists of preventing gait states where two neighbouring legs are lifted simultaneously. It is shown that, for a uniform translation with no spin, the free gait algorithm is optimal with respect to static stability.

On the gait control of a six-legged walking machine

Antipersonal mines kill or mutilate tens of people every day. Military mine clearance methods make use of heavy vehicles and cannot achieve a satisfying destruction percentage. Consequently, humanitarian deminers use the classical manual methods. This work is very tedious, dangerous and costly. The detection is not always reliable and is very slow. Improvements can be made by developing new sensors and by automating the detection sequence. The Robotics workgroup of the Belgian Hudem '97 project focuses on the development of low cost vehicles that could be equipped with mine detectors. In this paper, we first review the main characteristics of such platforms. We then show that the architecture of the vehicle is also determined by the chosen detection strategy. Afterwards, we describe in detail the original wheeled vehicle we are building. Its main characteristic is a very high mobility given by the 3 drive/steer wheels. The low-level control is made by a microcontroller, while paths are generated by the remote computer. Preliminary indoor test have demonstrated the potentialities of this vehicle.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Paul Alexandre

Papers

Gait analysis and implementation of a six leg walking machine

A conceptual walking vehicle for planetary exploration

On the gait control of a six-legged walking machine

Development of a high-mobility wheeled robot for humanitarian mine clearance

An Autonomous Micro Walking Machine with Articulated Body