Mobile Robots Introduction
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ERA-MOBI
Onboard PC
Laser Rangefinder
IR Floor Sensors
Sonar Sensors
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Onboard PC on ERA-MOBI vs Net-centric Robot Computing
Every ERA-MOBI has an onboard PC for control of the robot. We have chosen to mount the PC as a separate unit on top of the robot, rather than integrating a PC motherboard inside the robot. Why? So that the computer can be easily changed as better ones become available, and more processing power can be added to the robot. For example, you could add a new dual-core processor PC to the one already on the robot, and connect them with an ethernet cable, to provide a powerful processing setup for the robot. It would be very expensive and mechanically difficult to do the same thing with a motherboard inside the mobile robot.
The onboard PC is the key to making the ERA-MOBI platform responsive and autonomous. You can see the difference between a robot with and without an onboard PC below.
Offboard PC
In the picture below, the robot has a microcontroller, a laser rangefinder, and a wireless link to an offboard PC. The microcontroller can perform low-level motor control (for example, keeping the wheels turning at a constant speed), and also sends information from the laser rangefinder to the offboard PC. The PC interprets the rangefinder information, builds a map, and figures out where to send the robot. It then sends command to the microcontroller to move the robot accordingly.
If the wireless link is interrupted or slowed down, the robot cannot function. Wireless interruption can occur even when the distance between the wireless links is short - for example, as the robot moves, it might come near an electrical outlet whose interference blocks the wireless signal.
A wireless link to the PC also makes it difficult to achieve precise, realtime control of the robot. Even if information is sent out from the microcontroller at precise time intervals, the wireless link may clump them together, with irregular time intervals between sensor updates. Similarly, commands from the PC to the robot may experience delays, and the robot may take a long time to react to new information.
Onboard PC
In the picture below, the robot has an onboard PC. This PC, although small, is a fully-functional PC with the computational capabilities of a standard desktop PC. The onboard PC connects directly to the microcontroller and sensors, and can execute advanced robotic algorithms such as map-making and planning. It can send movement commands directly to the microcontroller, and react quickly to new information in the environment.
The onboard PC also has a wireless connection to the internet. It can send information across this link, to be displayed on any PC connected to the internet. Because the critical functions for robot autonomy reside on the robot, the wireless connection can slow down or disappear without affecting the performance of the robot. The onboard PC was a key element of the performance of the robots in the Centibots project at SRI International.
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