A Platform for Local Interactions between Robots in

A Platform for Local Interactions between Robots in Large Formations Ross Mead Jerry B. Weinberg Jeffrey R. Croxell

Problem swarm formation A Platform for Local Interactions between Robots in Large Formations

Background l Fredslund & Mataric 2002 l Balch & Arkin 1998 l Reynolds 1987 l Farritor & Goddard 2004 A Platform for Local Interactions between Robots in Large Formations

Formation Control l Utilize reactive robot control strategies ¡ closely couple sensor input to actions l Treat the formation as a cellular automaton ¡ lattice of computational units (cells) ¡ each cell is in one of a given set of states l governed by a set of rules A Platform for Local Interactions between Robots in Large Formations

Formation Control l A desired formation, F, is defined as a geometric description… ¡ i. e. , mathematical function ¡ F ← y = ax 2, where a is some constant F ← y = ax 2 A Platform for Local Interactions between Robots in Large Formations

Formation Control l A robot is chosen as the seed, or starting point, of the formation. F ← y = ax 2 seed A Platform for Local Interactions between Robots in Large Formations

Formation Control l The desired location on the formation is determined by calculating a relationship vector from c, … ¡ l where c is the formation-relative position (xi, yi) of the robot, … and the intersection of the function F and a circle centered at c with radius r, where r is the distance to maintain between neighbors in the formation. F ← y = ax 2 r 2 c ← (xi, yi) ← (x-cx)2 + (y-cy)2 r r seed A Platform for Local Interactions between Robots in Large Formations

Formation Control Relationships and states are communicated locally to robots in the seed’s neighborhood, which propagates changes in each robot’s neighborhood in succession. l Using sensor readings, robots attempt to acquire and maintain the calculated relationship with their neighbors. l F ← y = ax 2 r 2 c ← (xi, yi) ← (x-cx)2 + (y-cy)2 r r seed A Platform for Local Interactions between Robots in Large Formations

Formation Control l Despite only local communication, the calculated relationships between neighbors results in the overall organization of the desired global structure. F ← y = ax 2 r 2 c ← (xi, yi) ← (x-cx)2 + (y-cy)2 seed A Platform for Local Interactions between Robots in Large Formations

Formation Control l Thus, it follows that a movement command sent to a single robot would cause a chain reaction in neighboring robots, which then change states accordingly, resulting in a global transformation. seed A Platform for Local Interactions between Robots in Large Formations

Formation Control A Platform for Local Interactions between Robots in Large Formations

Formation Control l Likewise, to change a formation, a seed robot is simply given the new geometric description, and the process is repeated. F←y=0 seed A Platform for Local Interactions between Robots in Large Formations

Robot Platform l Each robot features: ¡ a Scooterbot II base l ¡ an l ¡a differential steering system XBC v 2 microcontroller executes formation control algorithm color-coding system and color camera l ¡ an l visual identification and tracking of neighbors XBee radio communication module sharing information within a robot’s neighborhood A Platform for Local Interactions between Robots in Large Formations

Robot Platform l Scooterbot II base ¡ precision cut double-decker base rigid expanded PVC l strong, but very light l ¡ 2" risers for additional decks ¡ differential steering system ¡ http: //www. budgetrobotics. com/ A Platform for Local Interactions between Robots in Large Formations

Robot Platform l XBC v 2 microcontroller ¡ executes formation algorithm ¡ back-EMF PID motor control ¡ fast charging l ~1 hour to fully charge ¡ http: //www. botball. org/ A Platform for Local Interactions between Robots in Large Formations

Robot Platform Starty l Color-coding system ¡ visual identification and tracking of neighbors Starty - IDy Starty - Stopy IDy - Stopy Robot. ID = IDmax * (Starty - IDy) / (Starty - Stopy) l Color camera ¡ multi-color, multi-blob simultaneous color tracking A Platform for Local Interactions between Robots in Large Formations

Robot Platform l XBee radio communication module ¡ ¡ ¡ ¡ ¡ sharing state information within a robot’s neighborhood Zig. Bee/IEEE 802. 15. 4 specification up to 65, 535 nodes on a network support for multiple network topologies low duty cycle long battery life collision avoidance retries and acknowledgements link quality indication 128 -bit AES encryption http: //www. maxstream. net/ A Platform for Local Interactions between Robots in Large Formations

References l Balch, T. & Arkin R. 1998. “Behaviorbased Formation Control for Multirobot Teams” IEEE Transactions on Robotics and Automation, 14(6), pp. 926 -939. l Fredslund J. , & Mataric, M. J. 2002. “Robots in Formation Using Local Information”, The 7 th International Conference on Intelligent Autonomous Systems, Marina del Rey, California. l Bekey G. , Bekey, I. , Criswell D. , Friedman G. , Greenwood D. , Miller D. , & Will P. 2000. “Final Report of the NSF-NASA Workshop on Autonomous Construction and Manufacturing for Space Electrical Power Systems”, 4 -7 April, Arlington, Virginia. l Reynolds, C. W. 1987. “Flocks, Herds, and Schools: A Distributed Behavioral Model, in Computer Graphics”, 21(4) SIGGRAPH ’ 87 Conference Proceedings, pages 25 -34. l Tejada S. , Cristina A. , Goodwyne P. , Normand E. , O’Hara R. , & Tarapore, S. 2003. “Virtual Synergy: A Human. Robot Interface for Urban Search and Rescue”. In the Proceedings of the AAAI 2003 Robot Competition, Acapulco, Mexico. l Farritor, S. M. , & Goddard, S. 2004. “Intelligent Highway Safety Markers”, IEEE Intelligent Systems, 19(6), pp. 811. A Platform for Local Interactions between Robots in Large Formations

Questions? For more information, visit the exhibition or http: //roboti. cs. siue. edu/projects/formations/