Roombots: Design and Implementation of a Modular Robot for Reconfiguration and Locomotion

In this thesis we present the design and implementation of a novel self-reconfiguring modular (SR-MR) robotic system: Roombots. We are aiming at three main applications with Roombots; locomotion through self-reconfiguration in the regular cubic 3D-lattice on structured surfaces, locomotion in non-structured environments applying central pattern generators (CPG) as the locomotion controller, and self-assembly and reconfiguration of static objects of the day-to-day environment, such as furniture. Robot assemblies from self-reconfigurable modular robots have the ability to adapt to a given task and working environment by altering their shape through a series of reconfiguration moves, and attachments and detachments between the modules. We are interested in self-reconfiguring modular robots for their shape-changing capabilities, and their distributed characteristics. We envision the following applications for Roombots: First, self-reconfiguration in a structured 3D lattice, i.e. a floor and walls equipped with connectors. Embedded connectors can provide pivot points for locomotion of SR-MR assemblies, and docking and recharging places for our adaptive furniture pieces. Second, our proposed concept for locomotion control of modular robots on non-structured ground are central pattern generators. Third, we would like to build adaptive and versatile furniture from modular robots and light-weight elements. In the following we are able to count more than 60 modular robotic systems, developed over the last two decades. However we were unable to identify an existing system which could provide us with all desired kinematic and geometric capabilities. This led us to design and implement a novel self-reconfiguring modular robotic system: Roombots. To tackle the module design we attempt to identify both meaningful design parameters from existing modular robots, and essential features for our applications. The combination of both leads to the kinematic and geometric description of the Roombots modules, and eventually to its implementation. In order to be able to assemble furniture from our Roombots units in the future, we need a reconfiguration framework which supports the specific requirements of Roombots. Metamodules made of two units attached in-series are attracted and guided by a virtual force-field, they use broadcast signals, look-up tables of collision clouds and simple assumptions about their near environment to reach their seeding positions, which are currently hand coded. For the task of locomotion in non-structured environments we propose a framework for learning to move with modular robots using central pattern generators and online optimization. The distributed implementation of CPGs offers an ideal substrate for producing locomotion patterns and for online learning, and an optimization framework for fast learning.

Learning to move in modular robots using central pattern generators and online optimization

Auke Ijspeert, Jérôme Maye

This article addresses the problem of how modular robotics systems, i.e. systems composed of multiple modules that can be configured into different robotic structures, can learn to locomote. In particular, we tackle the problems of online learning, that is, learning while moving, and the problem of dealing with unknown arbitrary robotic structures. We propose a framework for learning locomotion controllers based on two components: a central pattern generator (CPG) and a gradient-free optimization algorithm: Powell’s method. The CPG is implemented as a system of coupled nonlinear oscillators in our YaMoR modular robotic system, with one oscillator per module. The nonlinear oscillators are coupled together across modules using Bluetooth communication to obtain specific gaits, i.e. synchronized patterns of oscillations among modules. Online learning is done by running the Powell optimization algorithm in parallel to the CPG model, with the speed of locomotion being the criterion to be optimized. Interesting aspects of the optimization are: it is carried out online, it does not require stopping or resetting the robots, and it is fast. We present results showing the interesting properties of this framework for a modular robotic system. In particular, our CPG model can readily be implemented in a distributed system, it is cheap computationally, it exhibits limit cycle behavior (temporary perturbations are rapidly forgotten), it produces smooth trajectories even when control parameters are abruptly changed, and it is robust against imperfect communication among modules. We also present results of learning to move with three different robot structures. Interesting locomotion modes are obtained after running the optimization for less than 60 minutes.

2008

Roombots: Reconfigurable Robots for Adaptive Furniture

Aude Billard, Stéphane Bonardi, Pierre Dillenbourg, Auke Ijspeert, Rico Möckel, Soha Pouya, Alexander Spröwitz, Jesse van den Kieboom

Imagine a world in which our furniture moves around like legged robots, interacts with us, and changes shape and function during the day according to our needs. This is the long term vision we have in the Roombots project. To work towards this dream, we are developing modular robotic modules that have rotational degrees of freedom for locomotion as well as active connection mechanisms for runtime reconfiguration. A piece of furniture, e.g. a stool, will thus be composed of several modules that activate their rotational joints together to implement locomotor gaits, and will be able to change shape, e.g. transforming into a chair, by sequences of attachments and detachments of modules. In this article, we firstly present the project and the hardware we are currently developing. We explore how reconfiguration from a configuration A to a configuration B can be controlled in a distributed fashion. This is done using metamodules-two Roombots modules connected serially-that use broadcast signals and connections to a structured ground to collectively build desired structures without the need of a centralized planner. We then present how locomotion controllers can be implemented in a distributed system of coupled oscillators-one per degree of freedom-similarly to the concept of central pattern generators (CPGs) found in the spinal cord of vertebrate animals. The CPGs are based on coupled phase oscillators to ensure synchronized behavior and have different output filters to allow switching between oscillations and rotations. A stochastic optimization algorithm is used to explore optimal CPG configurations for different simulated Roombots structures.

2010

Legged locomotion with spinal undulations

Konstantinos Karakasiliotis

Legged locomotion with spinal undulations is a topic that has not received much attention yet in robotics, though, vertebrates depend on both their limbs and spine to move efficiently in their environments. In this thesis, my aim is to get more insights into the role and function of these two body parts as well as their coordination. Biology provides several answers to these questions. Salamanders and lizards are great biological paradigms for studying animal locomotion with limbs and flexible spine. Not only do they have a highly flexible spine and limbs that can sometimes vary in strength or even number, but they also demonstrate a rich repertoire of locomotor modes. They can walk on land, while they can swim and walk in water. This provides many more examples on the ways that limbs and spine function and coordinate. Biorobotics is a growing field of robotics that aims at answering questions that cannot be answered from animal observations. Those questions often deal with the development of a specific function of a body part. In my studies, I initially used a bio-inspired amphibious salamander-like robot Salamandra robotica II to extract basic principles of salamander locomotion. Although the improvements of the limb and tail designs enhanced the robot’s performance to a level that was surprisingly close to the salamander’s, several limitations were identified owing to the simplicity of the bio-inspired design. These limitations motivated me to design a new amphibious salamander-like robot, Pleurobot, which is capable of replicating the movements of salamanders with reasonable accuracy. A novel methodology was also used during this process which proved to be effective but simple at the same time. Three-dimensional kinematics of the salamander’s skeleton were recorded and used to guide the design process and optimization of the robot’s morphology and joints’ topology. The raw angular kinematics, extracted from X-ray biplanar videos of salamanders, were then used to drive the joints of Pleurobot, resulting in natural-looking and effective locomotion. The main contributions of this thesis are two-fold: i) biological data and robotic prototypes that improve our understanding on sprawling locomotion and ii) a successful methodology for robotic design for more animal-like robots and agile control

EPFL2013

Legged locomotion with spinal undulations

Konstantinos Karakasiliotis

EPFL2013