A Platform for Local Interactions between Robots in Large Formations

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

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

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

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

5. F ← y = ax2 Formation Control • A desired formation, F, is defined as a geometric description… • i.e., mathematical function • F ← y = ax2, where a is some constant A Platform for Local Interactions between Robots in Large Formations

6. seed Formation Control • A robot is chosen as the seed, or starting point, of the formation. F ← y = ax2 A Platform for Local Interactions between Robots in Large Formations

7. r r seed Formation Control • The desired location on the formation is determined by calculating a relationship vector from c,… • 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 = ax2 c ← (xi, yi) r2 ← (x-cx)2 + (y-cy)2 A Platform for Local Interactions between Robots in Large Formations

8. seed 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. • Using sensor readings, robots attempt to acquire and maintain the calculated relationship with their neighbors. F ← y = ax2 c ← (xi, yi) r2 ← (x-cx)2 + (y-cy)2 r r A Platform for Local Interactions between Robots in Large Formations

9. seed Formation Control • Despite only local communication, the calculated relationships between neighbors results in the overall organization of the desired global structure. F ← y = ax2 c ← (xi, yi) r2 ← (x-cx)2 + (y-cy)2 A Platform for Local Interactions between Robots in Large Formations

10. seed Formation Control • 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. A Platform for Local Interactions between Robots in Large Formations

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

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

13. Robot Platform • Each robot features: • a Scooterbot II base • differential steering system • an XBC v2 microcontroller • executes formation control algorithm • a color-coding system and color camera • visual identification and tracking of neighbors • an XBee radio communication module • sharing information within a robot’s neighborhood A Platform for Local Interactions between Robots in Large Formations

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

15. Robot Platform • XBC v2 microcontroller • executes formation algorithm • back-EMF PID motor control • fast charging • ~1 hour to fully charge • http://www.botball.org/ A Platform for Local Interactions between Robots in Large Formations

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

17. Robot Platform • XBee radio communication module • sharing state information within a robot’s neighborhood • ZigBee/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

18. Balch, T. & Arkin R. 1998. “Behavior-based Formation Control for Multi-robot Teams” IEEE Transactions on Robotics and Automation, 14(6), pp. 926-939. 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. Farritor, S.M., & Goddard, S. 2004. “Intelligent Highway Safety Markers”, IEEE Intelligent Systems, 19(6), pp. 8-11. Fredslund J., & Mataric, M.J. 2002. “Robots in Formation Using Local Information”, The 7th International Conference on Intelligent Autonomous Systems, Marina del Rey, California. Reynolds, C.W. 1987. “Flocks, Herds, and Schools: A Distributed Behavioral Model, in Computer Graphics”, 21(4) SIGGRAPH ’87 Conference Proceedings, pages 25-34. 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. References A Platform for Local Interactions between Robots in Large Formations

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