Page 37 - Introduction to Autonomous Mobile Robots

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Figure 2.8 Chapter 2
Static walking with six legs. A tripod formed by three legs always exists.

Figure 2.9 shows the Raibert hopper [28, 124], one of the most well-known single-
legged hopping robots created. This robot makes continuous corrections to body attitude
and to robot velocity by adjusting the leg angle with respect to the body. The actuation is
hydraulic, including high-power longitudinal extension of the leg during stance to hop back
into the air. Although powerful, these actuators require a large, off-board hydraulic pump
to be connected to the robot at all times.
Figure 2.10 shows a more energy-efficient design developed more recently [46]. Instead
of supplying power by means of an off-board hydraulic pump, the bow leg hopper is
designed to capture the kinetic energy of the robot as it lands, using an efficient bow spring
leg. This spring returns approximately 85% of the energy, meaning that stable hopping
requires only the addition of 15% of the required energy on each hop. This robot, which is
constrained along one axis by a boom, has demonstrated continuous hopping for 20 minutes
using a single set of batteries carried on board the robot. As with the Raibert hopper, the
bow leg hopper controls velocity by changing the angle of the leg to the body at the hip
joint.