  Prototyping robotic systems is a time consuming process. Computer aided
design, however, might speed up the process significantly. Quality-diversity
evolutionary approaches optimise for novelty as well as performance, and can be
used to generate a repertoire of diverse designs. This design repertoire could
be used as a tool to guide a designer and kick-start the rapid prototyping
process. This paper explores this idea in the context of mechanical linkage
based robots. These robots can be a good test-bed for rapid prototyping, as
they can be modified quickly for swift iterations in design. We compare three
evolutionary algorithms for optimising 2D mechanical linkages: 1) a standard
evolutionary algorithm, 2) the multi-objective algorithm NSGA-II, and 3) the
quality-diversity algorithm MAP-Elites. Some of the found linkages are then
realized on a physical hexapod robot through a prototyping process, and tested
on two different floors. We find that all the tested approaches, except the
standard evolutionary algorithm, are capable of finding mechanical linkages
that creates a path similar to a specified desired path. However, the
quality-diversity approaches that had the length of the linkage as a behaviour
descriptor were the most useful when prototyping. This was due to the
quality-diversity approaches having a larger variety of similar designs to
choose from, and because the search could be constrained by the behaviour
descriptors to make linkages that were viable for construction on our hexapod
platform.
