A dead reckoning (position) library (for NXT & robotc) to try out. It maintains global variable as to your robots location and heading without a compass, although a compass will help make it more accurate. And provide simple Piloting functions like move, turn, goto(x,y).
Please let me know of any problems you run into. I'm still working on a video explaining it, but as is usual for me, I got carried away and I am trying to do too much. (see update)http://www.spiked3.com/?p=410
The zip file has the LDD for my bot, but the library is generic and should work with any differential drive robots. Let me know if it does not.
update: man, this project has been a pain. I've been calling it localization for a while, and forgot, it's not really, it is dead reckoning. Localization involves using something in the environment to correct dead reckoning errors. So, even though I got a second wind to work on the video tutorial, I now have to go back and fix a bunch of voice overs. I gave up on finding something to use as a whiteboard. Any suggestions? Have you seen and/or know how they did the latest udacity videos?