  We study fixed assemblies of touching spheres that can individually rotate.
From any initial state, sliding friction drives an assembly toward a slip-free
rotation state. For bipartite assemblies, which have only even loops, this
state has at least four degrees of freedom. For exactly four degrees of
freedom, we analytically predict the final state, which we prove to be
independent of the strength of sliding friction, from an arbitrary initial one.
With a tabletop experiment, we show how to impose any slip-free rotation state
by only controlling two spheres, regardless of the total number.
