8. Walking Gaits and Motion Control

An omni-directional walking robot requires legs whose leg-tips can independently access 3-dimensional space. ‘Omni-directional’ means the ability to walk in all directions such that the walking robot is able to walk sideways left, sideways right, forwards and backwards, and turn left and right. Furthermore, possession of 3dof legs enables the robot to turn while translating, which is similar to ballroom dancers when they dance the Viennese waltz as already discussed in chapter 1. In fact other complex manoeuvres are possible that include maintaining the body in a level attitude as the legs negotiate uneven terrain. Such motion can be analysed as the body rotating about any Instantaneous Axis of Rotation (note, ‘axis’ as compared to ‘centre’) which is a three dimensional vector as compared to a two dimensional point. (This interesting problem serves as a mathematical challenge to students). The leg tip motion and the leg tip locus have been analysed in detail in chapter 4 so we now consider how leg tip motion can achieve walking gaits and motion control.