Page 14 - The Unofficial Guide to Lego Mindstorms Robots

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Mobile robots actually come in two varieties: tethered and autonomous. A tethered robot "cheats" by dumping its power
supply and brain overboard, possibly relying on a desktop computer and a wall outlet. Control signals and power are run
through a bundle of wires (the tether) to the robot, which is free to move around, at least as far as the tether will allow.

Autonomous mobile robots are even more challenging. These robots need to bring everything along with them, including a
power supply and a brain. The power supply is typically an array of batteries, which adds a lot of weight to the robot. The brain
is also constrained because it has to fit on the robot, not weigh a ton, and be frugal about sucking power out of the batteries.

This Is Tough Stuff

The field of autonomous mobile robotics is extremely challenging. Have you ever seen an autonomous mobile robot, besides in
the movies? Probably not. If you have been lucky enough to see such a robot, was it doing something useful? Probably not. If
the robot was supposed to do something useful, did it work? Probably not.

If it wasn't so hard to make autonomous mobile robots, the world would be full of them. Wouldn't it be nice to have a robot do
your laundry or drive you to the airport? But the cold truth is that it's unbelievably difficult to make a robot that can do even
the simplest of tasks. It all comes down to one fact: it's very hard to deal with the real world.

To understand this, think about how you might try to make a robot to vacuum your living room. This is a pretty simple task to
describe: basically you just want to move the vacuum back and forth over the rug until the whole thing is clean. Suppose you
modify your vacuum cleaner so that it can move around on its own, by adding more motors and a small computer brain. Just
consider the staggering complexity:

• How does the robot keep from getting tangled up in its own power cord, assuming it's a tethered robot? If it's not tethered,
you need to find a power supply that will run the robot for long enough to clean at least one room.

• How does the robot know where it's been already? How does the robot know where it is? How does it know where to go
next?

• How does the robot navigate around obstacles like table legs and furniture?

• How does the robot recognize things it shouldn't vacuum, like money, or toys, or your cats?

You can answer these questions, but not well, not simply, and not cheaply. After years of sweat and expense, you might
produce a robot that could vacuum a room, but only under very closely controlled conditions. Add a rocking chair, or drop a
child's toy in the middle of the room, and you'd probably have to start all over again.