Shape Formation by Self-Disassembly in Programmable Matter Systems by Kyle William Gilpin B.S., Massachusetts Institute of Technology (2006) M.Eng., Massachusetts Institute of Technology (2006) Submitted to the Department of Electrical Engineering and Computer Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering and Computer Science at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2012 c Massachusetts Institute of Technology 2012. All rights reserved. Author............................................. ...................... Department of Electrical Engineering and Computer Science May 22, 2012 Certifiedby......................................... ...................... Daniela Rus Professor Thesis Supervisor Acceptedby......................................... ..................... Leslie A. Kolodziejski Chair, Department Committee on Graduate Students 2 Shape Formation by Self-Disassembly in Programmable Matter Systems by Kyle William Gilpin Submitted to the Department of Electrical Engineering and Computer Science on May 22, 2012, in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering and Computer Science Abstract Programmable matter systems are composed of small, intelligent modules able to form a vari- ety of macroscale objects with specific material properties in response to external commands or stimuli. While many programmable matter systems have been proposed in fiction, (Barbapapa, Changelings from Star Trek, the Terminator, and Transformers), and academia, a lack of suitable hardware and accompanying algorithms prevents their full realization. With this thesis research, we aim to create a system of miniature modules that can form arbitrary structures on demand. We develop autonomous 12mm cubic modules capable of bonding to, and communicating with, four of their immediate neighbors. These modules are among the smallest autonomous mod- ular robots capable of sensing, communication, computation, and actuation. The modules employ unique electropermanent magnet connectors. The four connectors in each module enable the mod- ules to communicate and share power with their nearest neighbors. These solid-state connectors are strong enough for a single inter-module connection to support the weight of 80 other mod- ules. The connectors only consume power when switching on or off; they have no static power consumption. We implement a number of low-level communication and control algorithms which manage information transfer between neighboring modules. These algorithms ensure that messages are delivered reliably despite challenging conditions. They monitor the state of all communication links and are able to reroute messages around broken communication links to ensure that they reach their intended destinations. In order to accomplish our long-standing goal of programmatic shape formation, we also de- velop a suite of provably-correct distributed algorithms that allow complex shape formation. The distributed duplication algorithm that we present allows the system to duplicate any passive object that is submerged in a collection of programmable matter modules. The algorithm runs on the processors inside the modules and requires no external intervention. It requires O(1) storage and O(n) inter-module messages per module, where n is the number of modules in the system. The algorithm can both magnify and produce multiple copies of the submerged object. A programmable matter system is a large network of autonomous processors, so these algo- rithms have applicability in a variety of routing, sensor network, and distributed computing appli- 3 cations. While our hardware system provides a 50-module test-bed for the algorithms, we show, by using a unique simulator, that the algorithms are capable of operating in much larger environments. Finally, we perform hundreds of experiments using both the simulator and hardware to show how the algorithms and hardware operate in practice. Thesis Supervisor: Daniela Rus Title: Professor 4 Acknowledgments Many people deserve my gratitude and thanks for helping to make this thesis a reality. First, my advisor, Daniela Rus, was instrumental in the process. I have been incredibly fortunate to find such an amazing advisor who’s always been a staunch ally and a supportive mentor. More than anything, Daniela has taught me to dream big. My committee members, Rob Wood and Anantha Chandrakasan, also deserve a great deal of thanks. Not only have Rob and Anantha provided useful feedback as I have developed my thesis, they have been long-term collaborators and mentors as well. Under Anantha’s guidance, I had the chance to develop several high-performance FPGA systems that were essential in securing my first job outside academia. Rob has been an ideal collaborator as part of the DARPA Programmable Matter project. From day one, he has been incredibly generous with his time and equipment, no questions asked. Ara Knaian developed the electropermanent magnets that are essential to the Smart Pebble modules. Ara was always full of energy and wild ideas. Fueled by Ara’s enthusiasm alone, we painstakingly built more than 250 electropermanent magnets by hand. Kent Koyanagi helped with the Robot Pebbles project over the course of two summers. Kent’s dedication and work ethic were amazing. Despite some awfully boring tasks, he never complained, and he often was in lab for longer hours than I was. I also owe my thanks to my fellow graduate students in the Distributed Robotics Laboratory. Few groups function so well together with so little conflict or competition. In particular, there are several alumni who were instrumental to my quick integration and success with the group: Keith Kotay, Marty Vona, Carrick Detweiler, and Iuliu Vasilescu. Outside of MIT, I have the BMG to thank for reminding me not to take life too seriously. Scott, Eric, Sangeen, Brad, KC, Mahmoud, Ihsanul, Matt, Joe, and Paul, thanks for all the good times. Finally, I have my parents, Bill and Linda, sister, Amy, and wife, Erin to thank for their sup- port, encouragement, and understanding. My parents fostered my love of all things electronic and mechanical from an early age with many trips to yard sales for old radios and record players to take apart in the basement. As I grew older, there was never a shortage of Capsella modules, Radio 5 Shack electronic project kits, Legos, and, most important, encouragement to explore. Amy, you were always a good, if not willing, test subject for my contraptions. More importantly, you have always taken interest in my life and, by doing so, encouraged me to aim high. Erin, your generos- ity, unwavering support, perpetual excitement, and reminders that there are more important things in life than working all the time have been essential. I could not ask for a better partner, and I could not have done this without you–thank you. This work was supported by DARPA and the US Army Research Office under grant number W911NF-08-1-0228, NSF EFRI grant number 0735953, Intel, and the NDSEG fellowship pro- gram. 6 Contents 1 Introduction 17 1.1 Challenges...................................... 19 1.2 CurrentStateoftheArt . .. .. .. .. .. .. .. .. .... 21 1.3 OurApproach..................................... 22 1.3.1 Self-AssemblyandDisassembly . .... 25 1.3.2 DistributedDuplication. .... 26 1.4 ThesisContributions . .. .. .. .. .. .. .. .. .... 27 1.5 ThesisOutline................................... .. 30 2 Related Work 33 2.1 ModularRobotics................................. .. 34 2.1.1 ChainSystems ................................ 35 2.1.2 LatticeSystems................................ 36 2.1.3 TrussSystems ................................ 39 2.1.4 Free-FormSystems.............................. 39 2.2 OtherProgrammableMatterSystems. ....... 40 2.3 Self-AssemblingSystems. ..... 41 2.4 SimplifyingShape Formation by Self-Disassembly . ............ 42 2.5 Simulators...................................... 43 3 Hardware 45 3.1 ConnectionMechanism. ... 48 7 3.1.1 ElectropermanentMagnetTheory . .... 49 3.1.2 ElectropermanentMagnetConstruction . ....... 52 3.2 PowerElectronics................................ ... 53 3.3 Processors...................................... 55 3.4 Bonding........................................ 55 3.5 Communication................................... 59 3.6 Power ......................................... 61 3.7 TestFixture ..................................... 64 3.8 3DModules...................................... 66 3.9 Miniaturization ................................. ... 68 3.9.1 ConnectorTechnologies . .. 69 3.9.2 UnitModuleFabrication . .. 72 4 The Sandbox Simulator 75 4.1 SimulatorDesign ................................. .. 78 4.2 ProcessDistributionandCodeReuse. ........ 80 4.3 Communication................................... 81 4.4 Extensibility................................... ... 84 4.5 Front-endandSimulatedRobotSeparation. .......... 84 4.6 Experiments..................................... 86 5 Low Level Communication 89 5.1 MessageBuffers .................................. 90 5.2 PacketFormat.................................... 93 5.3 Packet-LevelExperiments . .100 5.4 ApplicationMessageFormat . .103 5.5 MonitoringLinkState. .. .. .. .. .. .. .. .. .107 5.6 Robustness:RespondingtoBrokenLinks . ........110 5.7 LinkStateExperiments . .114 8 5.8 Two-DimensionalRouting . .116 5.8.1 RoutingAlgorithm .............................. 116 5.8.2 ExperimentalResults. 117 6 Shape Formation Basics 123 6.1 Sculpting