> There are commercial slip ring assemblies, but they are VERY dear.

I work in a university research lab, and we've purchased a few (some  
for many thousands).  If you're not looking for very high rpm/low  
torque/low noise, there are actually some reasonable assemblies out  
there.  Just a few months ago, we purchased a 12-channel assembly  
from Moog components (polysci.com) for about $150.  It's the AC6023,  
and is very compact; rated for 2A, 220VAC, and 250rpm.  We haven't  
used it extensively (yet), but it seems to work as prescribed.  It  
may be worth your while to give them a call -- they may have  
something for less than you can make on your own.

-Matt
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