Page 109 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 6

802.11 802.11 Ethernet
Lap Top
Ethernet Ethernet Camera
Master Computer
Access Point Radio
Slave 2 Xducers
(Sonar)

Ethernet Access Point Slave 3 Ranger
802.11
Laser
Ethernet
(Lidar)

Host
Computer Mobile Robot

Figure 6.7. Communications structure based entirely on Ethernet

If one does not immediately appreciate the elegant simplicity that wireless Ethernet
systems have brought to mobile robots, it is instructive to see how things were done
only a few years ago. Figure 6.8 is the equivalent system as implemented for the SR-2
system fielded by Cybermotion before 1998. Since only low-speed radio modems were
available, video had to be sent over separate channels. As robots moved through
facilities, they would exceed the range of both systems.
Radio repeaters would relay the data channel to the robot, but at the expense of
bandwidth. Video, however, could not be handled by repeaters and each receiver was
connected to a switch. As the robot moved from location to location, the host
computer would send commands to the switch to select the nearest video receiver.
Actually, things were even messier than this when two-way voice communications
were required. In these situations, yet another transceiver was added to the robot.

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