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3. Have a robot competition. In Chapter 9, RoboTag, a Game for Two Robots, I'll talk about one possible robot competition. There are many other types of competitions. You and a friend could
build robots to accomplish a specific task. Then you could see whose robot performs better. The "Online Resources" section at the end of this chapter lists some existing competitions.
You might think that having three or more RCXs would be even better, but it actually complicates things considerably. Although IR communication between two RCXs is fairly straightforward, it
gets messy with three or more RCXs. How do you know if an IR message is destined for a specific RCX? A simple solution is to assign a specific range of message values to various message
pathways. For example, with three RCXs, named RCX1, RCX2, and RCX3, you might assign the message numbers as shown in Table 7-1.
Table 7-1. Sample Message Assignments for Three-way RCX
Communication
Message Numbers Message Pathway (Two-way)
0 to 9 RCX1 to RCX2
10 to 19 RCX1 to RCX3
20 to 29 RCX2 to RCX3
A more general solution may someday be supplied by the LEGO Network Protocol, a work in progress in the online MINDSTORMS community (see the "Online Resources" for more
information).
The Allure of Telerobotics
Replacing the function of your robot's brain with that of a human brain is appealing in many situations. It's easy to program a robot to do the same task over and over again. However, if the task
changes or if the environment changes, the robot may have a hard time adjusting. Humans are much better at adapting to new conditions.
On the other hand, telerobotics is a kind of cheating. Part of the point of autonomous mobile robots is that you can set them running and forget about them until they're done with whatever they're
doing. If you build a robotic vacuum cleaner, you want to set it running and forget about it until it's done cleaning your floors. If you used a teleoperated robotic vacuum cleaner, you'd spend just
as much time cleaning as with a conventional vacuum cleaner.
In the simplest form of telerobotics, the human can see the robot and can control it much as you might play with a radio control car. This is basically how the remote control for Minerva works:
you can see Minerva and control it by sending IR messages from the remote control.
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More sophisticated telerobots have a video camera that sends pictures back to a human operator. The operator can see what the robot sees and can send commands to control the robot.
Teleoperation does not work well if the human operator and the remote robot are separated by a very large distance, such as the distance between Mars and the Earth. In this case, the video signals
from the robot take a long time to reach the operator, and the control signals from the operator take a long time to reach the robot. What the operator sees is really a second or two behind what's
actually happening, so it's very hard to control the robot with any precision.
Fortunately, you don't have to worry about this with Minerva. Because the remote and the robot communicate with IR light, there must always be a line-of-sight between them. If you can control
the robot, you can see it—there's no video connection to add confusion.
Building Instructions
The controls for the remote are built on the bottom of the RCX. This was a conscious design decision—it orients the IR port of the remote in the best place to broadcast commands to Minerva.