Locomotion Analysis of Hexapod Robot

Abstract

flexible gait allowed it to overcome complex terrains, but its configuration was quite complicate for control system design. R Hex, introduced by Uluc et al. in 2001, is another hexapod robot with half-circle legs with a simple alternate tripod gait. Most popular hexapods can be grouped into two categories, rectangular and hexagonal ones. Rectangular hexapods have a rectangular body with two groups of three legs distributed symmetrically on the two sides. Hexagonal hexapods have a round or hexagonal body with evenly distributed legs. The gait of rectangular six-legged robots has motivated a number of theoretical researches and experiments which nowadays reached to some extent a state of maturity. In 1998 Lee et al. showed for rectangular hexapods the longitudinal stability margin, which is defined as the shortest distance from the vertical projection of center of gravity to the boundaries of the support pattern in the horizontal plane, of straight-line motion and crab walking. Song &Choi in 1990 defined the duty factor as the fraction of cycle time in which a leg is in the supporting phase and they proved that the wave gait is optimally stable among all periodic and regular gaits for rectangular hexapods when 3/4 1. Both the tripod gait and the problem of turning around a fixed point on an even terrain have been widely investigated and tested for a general rectangular hexapod with three DOF legs The so called 4+2 quadruped gaits A series of fault-tolerant gaits for hexapods were analyzed by Yang et al. [Yang & Kim, 1998a, 1998b, 2000 and 2003]. Their aim was to maintain the stability in case a fault event prevented a leg from supporting the robot. In 1975, Kugushev and Jaroshevskij proposed a terrain adaptive free gait that was non-periodic. McGhee et al. in and other researchers [Porta & Celaya, 2004; Erden & Leblebiciogl] went on studying free gaits of rectangular hexapod robots. At the same time, the hexagonal hexapod robots were studied with inspiration from the insect family, demonstrate better performances for some aspects than rectangular robots. Kamikawa et al. in 2004 confirmed the ability to walk up and down a slope with the tripod gait by building a virtual smooth surface that approximates the exact ground. Yoneda et al. in 1997 enhanced the results of Song & Choi in 1990, developing a time-varying wave gait for hexagonal robots, in which velocity, duty factor and crab angle are changed according to terrain conditions. A. Preumon et al. in 1991 proved that hexagonal hexapods can easily steer in all directions and that they have longer stability margin, but he did not give a detailed theoretical analysis. Takahashi et al. in 2000 found that hexagonal robots rotate and move in all directions at the same time better than rectangular ones by comparing stability margin and stroke in wave gait, but no experimental results were presented. Chu and Pang in 2002 compared the fault tolerant gait and the 4+2 gait for two types of hexapods of the same size. They proved theoretically that hexagonal hexapod robots have superior stability margin, stride and turning ability compared to rectangular robots. It is also worth to mention here a work carried out by Gonzale de Santos et al. [Gonzale de Santos et al., 2007a and Gonzale de Santos et al., 2007b]. They optimized the structure of rectangular hexapods and found that extending the length of middle legs of rectangular robots helps in saving energy. This outcome can be seen as a transition from rectangular sixlegged robots to hexagonal ones.