Abstract-LDP (Locally Distributed Predicates) is a distributed, high-level language for programming modular reconfigurable robot systems (MRRs). In this paper we present the implementation of two motion-planning algorithms in LDP, and analyze both their performance and ease of implementation. We present multiple variations of one planner, including a novel resource allocation algorithm. We then draw conclusions about both the utility of the motion-planning algorithms and the suitability of LDP to the problem space. Our experiments suggest that metamodule-based planning approaches have a cost in time and/or energy terms, but that the cost can be worth paying in exchange for the additional generality and separationof-concerns offered by these techniques. The particular tradeoff for a given system will depend upon its goals and the details of the underlying modules.
I. MRRS AND MOTION PLANNINGThe problem of reconfiguration / shape planning for modular robotic systems (MRRs) presents several challenges over and above those found in non-modular robots. The large number of discrete modules results in a correspondingly large number of degrees of freedom, and creates a very large state space that a planner may have to explore. Furthermore, the motions of individual modules are often restricted in non-trivial ways, e.g., moving a module to an adjacent empty space may require many other modules to move out of the way due to blocking constraints. Essentially, two configurations that are similar in state space, may actually be separated by a long reconfiguration path.Two recent approaches attempt to overcome blocking constraints and allow scalable, disconnection-free, stochastic planning in large MRRs. A scaffold-based technique [1] restricts modules to a specific grid structure that allows other modules to pass through unhindered. More recent work [2] groups modules together into metamodules and provides a high-level set of primitives that are not subject to blocking constraints. Both allow greedy or stochastic shape planning to succeed. However, the metamodule system is more general, and can be implemented on a variety of different MRR designs. The question we seek to answer is what price does one pay, if any, for this added generality? In this paper, we compare these approaches to scalable shape change, using LDP [3], a system for concisely representing distributed programs for MRRs. As part of this study we illustrate the capability of LDP to enable rapid and concise
A. The Shape Change ProblemThe shape change problem considered in this paper is the reconfiguration of a large lattice-style MRR from a starting shape to a target shape. We assume that the system is provided with a target shape (e.g., list of desired module positions, variably-sized blocks [1], or isosurface equations). Furthermore, we assume that the modules are aware of their locations in the initial shape, either through a-priori knowledge (e.g. from the structure of the lattice), or from a localization algorithm [4], [5].All communication within large ...