Figure 1.

Four dynamic walking models. (a) McGeer (1990b) demonstrated gravity-powered walking with knees. The model walks down a gentle slope, with a gait generated entirely by the passive dynamics of the limbs. The knee provides automatic ground clearance for the swing leg's foot. (b) Kuo (2002) showed that a push-off impulse could power straight-legged gait on level ground, with a hip spring modulating step frequency for faster, economical walking. Here we consider (c) a powered kneed model with uni-articular hip and/or knee springs, as well as (d) bi-articular springs acting across both knee and hip. Separate models are depicted with a common hip trajectory. See table 1 for dimensions in (a).