Two robots working together

This video shows how two robots are working together. At the beginning, the master node sends out instructions that robot 1 is working and robot 2 is charging. Then robot 1 moves in zigzag trying to cover the area, and robot 2 is waiting in charging area. When robot 1 is "running out of charge", it sends a message to master with its current location. When it receives master's feedback, it starts moving to the charging area. In the meanwhile, robot 2 gets master's instruction with the position to start. Robot 2 moves to the specific position.