Chaotic physical systems as random number sources

I'm curious if anyone knows of any attempts to use a chaotic physical system (such as the famous double pendulum) as a source of random numbers. I did an Alta Vista check on the problem, and all I turned up was a paper (in postscript, so I couldn't read it) on all mathematical pseudorandom number generators being logical chaotic systems. (It's at http://csl.ncsa.uiuc.edu/~herring/publications/rand.ps). One problem that I can see is that of strange attractors. While the path through each time would be different, they're still _close_ to each other, and a practical mechanical system might not be sensitive enough to pick up the differences. Thanks, -Allen