Search Space Analysis of Evolvable Robot Morphologies

Abstract

We present a study on morphological traits of evolved modular robots. We note that the evolutionary search space-the set of obtainable morphologies-depends on the given representation and reproduction operators and we propose a framework to assess morphological traits in this search space regardless of a specific environment and/or task. To this end, we present eight quantifiable morphological descriptors and a generic novelty search algorithm to produce a diverse set of morphologies for any given representation. With this machinery, we perform a comparison between a direct encoding and a generative encoding. The results demonstrate that our framework permits to find a very diverse set of bodies, allowing a morphological diversity investigation. Furthermore, the analysis showed that despite the high levels of diversity, a bias to certain traits in the population was detected. Surprisingly, the two encoding methods showed no significant difference in the diversity levels of the evolved morphologies or their morphological traits.

Lamarckian Evolution of Simulated Modular Robots

“…Zhang and Shasha ( 1989 ). Second, we consider the phenotypes and characterize the forms of the robots through seven different morphological descriptors, size, symmetry, proportion, number of active joints, coverage, length of limbs, number of limbs , after Miras et al ( 2018 ). Details are given in Appendix 2 .…”

Morphological Attractors in Darwinian and Lamarckian Evolutionary Robot Systems

“…For the analysis of the morphological properties of the evolved populations we measure and compare a set of morphological descriptors [22]. The morphological descriptors are a tool for quantifying the properties of each robot's morphology.…”

“…Recent research explores the influence of fitness functions on the outcome of evolution [21]. The basis for this research is the morphological descriptors defined in [22] along with [16].…”

Insights in evolutionary exploration of robot morphology spaces

“…For analyzing the morphological properties of the robots, we used a framework proposed in our previous work [1], [2] containing nine morphological descriptors. The descriptors, for which a more detailed explanation can be found in our previous work, range from 0 to 1 and are named: Branching,…”

“…To this end, we have identified several morphological properties, e.g., size, symmetry, branching, that together span a multidimensional search space for evolution in [1]. In a followup study we have investigated how these evolved morphological properties change when using different criteria for selection, cf.…”