On Tue, 31 Jan 2006 07:48:13 +0800, "Ravi Shankar Nair"
<sujashankar@pacific.net.sg> wrote, quoted or indirectly quoted
someone who said :

your basic device you need is a accelerometer with a wireless
connection. GPS would not be useful at those small distances.

Another sort of device you could use in the thing Polaroid used in its
SX-70 cameras.  They bounced a beam of sound, ultrasound, ? and
listened for the echo to get distance.  You could use them pointed in
various direction to measure distance to the nearest wall.

If the thing in on wheels, you can measure rotation very easily with a
square wave detector mounted on the axle -- the sort the old
mechanical mice used.

You could mount an optical mouse on the bottom of the device and have
it scan the carpet as is goes rolling by. That would be the cheapest
way to fly.  Years ago Logitech sent me a book on how to write mouse
drivers  -- how these things work at the lowest level.