Meeting Abstract
Bipedal walking is central to our lives yet it cannot be fully understood by studying a single species. Taking a broadly comparative approach, we analyze the walking of 1) humans, 2) birds, 3) simulations of simple models – the inverted pendulum (IP) and bipedal spring-loaded inverted pendulum (BSLIP), and 4) current bipedal robots that embody the IP and BSLIP. For birds and humans, we determined the center of mass dynamics for a full stride of walking using a series of force platforms. Walking simulations were done in Matlab using published code for the IP and BSLIP and metrics for walking robots were taken from the literature. We recorded the walking and running speeds used by birds, along with a range of speeds from the slowest walking through slow running for humans (dimensionless speeds from 0.3 to 1.3). Humans walked at dimensionless speeds between 0.31 and 0.78, whereas birds transition to running before reaching humans’ preferred walking speed of about 0.5. Walking speed is limited in both the BSLIP and IP models because they become ballistic at dimensionless speeds of 0.44 and 0.78, respectively. Birds and humans show consistently flat trajectories across the full range of human walking speeds. In contrast IP and BSLIP models have much greater vertical oscillations, with velocity angles becoming two- to three-fold greater than those of birds or humans as walking speed increases. Hence, current walking models produce markedly different center of mass dynamics than those of living bipeds at all but the slowest speeds. In fact, bipedal robots such as Cornell Ranger (IP-based) and ATRIAS (BSLIP-based) walk at such low dimensionless speeds of 0.19 and 0.32, respectively.
