The Active Body
Honda’s Asimo (see fig. 1.1) is billed, perhaps rightly, as the world’s most advanced humanoid robot. Boasting a daunting 26 degrees of freedom (2 on the neck, 6 on each arm, and 6 on each leg), Asimo is able to navigate the real world, reach, grip, walk reasonably smoothly, climb stairs, and recognize faces and voices. The name Asimo stands (a little clumsily perhaps) for Advanced Step in Innovative Mobility. And certainly, Asimo is an incredible feat of engineering, still relatively short on brainpower but high on mobility and maneuverability.
As a walking robot, however, Asimo is far from energy efficient. For a walking agent, one way to measure energy efficiency is by the so-called specific cost of transport (Tucker 1975)—namely, “the amount of energy required to carry a unit weight a unit distance.”1 The lower the number, the less energy is required to shift a unit of weight a unit of distance. Asimo rumbles in with a specific cost of transport of about 3.2, whereas we humans display a specific metabolic cost of transport of about 0.2. What accounts for this massive difference in energetic expenditure?
Whereas robots like Asimo walk by means of very precise, and energy-intensive, joint-angle control systems, biological walking agents make maximal use of the mass properties and biomechanical couplings