|For a project I wanted to have fluorescent light tubes turn while they were powered up. I needed four wires connecting the ballast with the tubes.
This is a How-To for a Slip Ring Connector using ball bearings.
(I have more and detailed images at www.stephanschulz.ca/sts/howto/newSlipring/index.html)
"A slip ring (in electrical engineering terms) is a method of making an electrical connection through a rotating assembly." (source: wikipedia.org)
I bought ball bearings from kinecor.com. Their width, inner and outer diameter determine the size of all the other parts.
I also got some clear plastic tubing. The bigger one fits the ball bearing snug inside and the smaller one fits inside the bearings. Make sure that the axle still has enough space to slip easily inside the smaller plastic tube. If needed you could combine different sizes of tubing until you reach the right size.
I used a piece of brass stock as my axle extension. O-rings, small screws and terminal blocks were needed to.
I cut the brass to the right size and drilled a hole in one end. The motors axle will fitted in here. A small threaded hole at the side allowed me to use a screw to hold both axles in place.
I dremeled four groves in brass axle deep enough for the wires to fit and not stick out more then the diameter of the axle. The wire does have insolation which can be squished a bit but try to dremel the grove deep enough.
Then I slipped the smaller plastic tube over the axle and marked where I wanted the wires to come out. I also temporarily slip on the bearings and O-rings to get the right spacing and position. I also marked which groves goes with which hole. My groves were not evenly spaced so I wanted to make sure that the marked hole will go with the right groves.
I cut the smaller piece of plastic tubbing so that it would fit all four ball bearings plus O-rings that go between them. The rubber O-rings prevent the bearings to ever touch each other. Then one by one I stuck a piece of wire with just a bit of uninsulated wire through. I had to make sure that a bit of the insulates was sticking out to. Then I placed the O-ring and then slowly pushed the ball bearing over the wire. I ground a small grove in the inside of the bearing for the wire to have a bit of space. So make sure the grove and the wire are aligned.
Then I slowly pushed the axle in. Now it was helpful that I marked which grove goes with which wire because I was a bit scared to cut the insulation. This would be dangerous because power would run through the axle all over the place!
I took the bigger piece of plastic tubbing slipped and marked where I needed the threaded holes to go. I used small steal screws and cut of their heads after I screwed them in tight.
I also ground a bit of the inside of the tube away so that it would fit better with the motor. My motor had round part sticking out. After grinding the tube it then gave me a tight fit and prevented the tube from moving around too much.
I used terminal block to create a safe connection to any power cable that I wanted to attach to the slip ring connector.
Here you can see the finished connector. I used a lot of O-rings in different places, because I wanted to be sure that no wires gets slowly worn out, cut or any uninsulated wire could be accidentally touched.
I have more and detailed images at www.stephanschulz.ca/sts/howto/newSlipring/index.html
I also have some images of an older design at www.stephanschulz.ca/sts/howto/oldSlipring/index.html
Thanks to Peter Flemming for the idea of using ball bearings.