[Al Skierkiewicz]

Steve,
You asked an engineering question, so I gave you an answer. I didn't say it was a good one. There is no possible way to not have some noise in a slip ring, particularly one that is carrying a lot of current. However, with large brushes or multiple brushes, you should be able to transfer enough current to be useful. Slip rings for sensor use should be fine since the current is fairly low, and the noise should also be low. Please be sure that power supply for sensors are filtered near the sensor.
There are some mercury filled rotary electric connections out there. I am against using them but I do believe the GDC answered (In a Q&A) that they could be used this year. In the hard hits, and misalignments I see on robots during inspection, I believe the chance for a mercury spill is pretty high. For that reason, I advise against their use.