Please enable Java for an interactive construction (with Cinderella). For a given configuration, a placement is said to be stable if the following condition holds:

G CH ({pi, i I})

where CH(S) denotes the convex hull of S. A robot configuration is stable if there is a stable placement for the configuration.
The spider on the left depicts a stable placement. Click link for Unstable placement
Spider Home

Created with Cinderella