This New York Times article on Creepy-Crawly Robotics highlights the ascendancy of “biologically inspired” design ideas in robotics. Some sense of the impact of this idea can be seen in the following sequence of 4 videos about a challenging mobility problem: bipedal walking. It is very hard to get a two-legged robot to walk about a room, much less step up a curb or down a flight of stairs, without it landing in a heap. Compare this mechanical mummy-walk (exhibit 1) to Martijn Wisse’s elegant design study at Cornell (exhibit 2) of an old toy patent from 1912, for instance. It is simply gravity and mechanical design that propels Wisse’s design down the ramp; see here those same principles applied to a level-ground walker (exhibit 3) from Jim Collin’s laboratory. Finally, and most recently, this cool dinosaur (exhibit 4) from Gil Pratt’s MIT LegLab is simply stunning.
There are two different ideas at play here. The first, which is the approach behind the mechanical mummy clip and older robotic technologies like the arm on the space shuttle, is to view walking (or grabbing stuff in space) as foremost a control problem. Say you’ve got a leg with a hip, knee, and ankle, which you construct from a series of joints that can each be moved to n different positions. This means that the foot attached to the end of your ankle can be in one of 3n different positions with respect to the torso it is attached to. Standing, walking, running all live in this space, the thinking runs; and if it doesn’t come off in practice, then simply increase the flexibility of your joints by increasing the size of n. The problem is that increasing the size of n increases the complexity of the control problem: there’s more options to choose, which means more processing to be done, and to be done quickly, which translates to more energy and resources required to “think” out each move. This is often a theoretician’s approach to robotic problems, and is often undone by practice. The insight illustrated by these videos is that getting a thing to walk, rather than proving that it should be able to, necessitates reducing the complexity of the control problem. And this serious constraint on resources changes the nature of the problem.
The biologically inspired approach to robotics in this case looks for clever ways to cut down on the space of possibilities by looking to see how biology pulls off similar tricks, rather than following mechanical or artificial constraints. It should be stressed too that one might also radically change scale and look to micro-organisms for inspiration, like this very cool NASA mobility concept study.
In the case of bipedal walking, the interesting insight behind this selection of videos is the benefit from viewing the walking problem to involve more than simply how to orient a pair of 3-jointed limbs, but instead to view walking as an activity of a dynamic system where the control of the moving parts is restricted (and in part, solved) in virtue of their role within the system. Walking involves swaying hips and moving arms. It is more dance than determination. In the dinosaur example, there are a lot of joints (it is a 16 degree of freedom system!), but movement of these joints is restricted both mechanically and by software to model the skeletal and muscular structure of a dinosaur. On top of this, its got a long tail and a heavy head stretched out front to back to help stabilize it, like a tightrope-walker’s pole.
Philosophy is a theoretician’s game, but there are branches which purport to address practical matters, such as decision and reasoning. There are arguments for resource-bounded decision and rationality that are perfectly analogous to the illustrated story I’ve told here about robot mobility, but my sense is that these arguments have yet to be fully engaged. Perhaps movie clips of mechanical mummies and robotic dinosaurs will soften some to the general idea behind these arguments.