  Linkages are mechanical devices constructed from rigid bars and freely
rotating joints studied both for their utility in engineering and as
mathematical idealizations in a number of physical systems. Recently, there has
been a resurgence of interest in designing linkages to perform certain tasks
from the physics community. We describe a method to design the topology of the
configuration space of a linkage by first identifying the manifold of critical
points, then perturbing around such critical configurations. We then
demonstrate our procedure by designing a mechanism to gate the propagation of a
soliton in a Kane-Lubensky chain of interconnected rotors.
