The best place for research on hurdy-gurdy's is http://www.hurdygurdy.com/hg/hghome.htmlBriefly, a hurdy-gurdy has a crank attached to a wheel (4'-7") which spins against several strings, like a violin bow rubs against strings. Some strings are drones, while other strings go through a box with buttons in a standard keyboard pattern. The buttons push against the melody, or chanter, string(s), which shorten them and raises the pitch.
These instruments sound like a small bagpipe with violin-like tone, with some small rattling mechanical noises also. Very medieval tone!
Dave :^)