What’s In A Slip Ring?

We know that when [Big Clive] puts up another video, the chances are we’re in for another fascinating look into a piece of tech on his bench. The latest is a slip ring assembly, and he gives it a teardown to reveal its secrets.

For most of us, the only place we encounter a slip ring is in some electric motors or alternators when it provides a connection via a conductive ring and a graphite brush from a fixed component to a rotating one. But they also appear as components in their own right wherever a rotating assembly needs an electrical contact, and it’s one of these that [Clive] has on his bench. It’s a compact unit with an impressive six conductors, and its manufacturer boldly claims that it’s good for mains voltages. We’re going with the verdict in the video below the break. That’s wishful thinking, given the size of the unit.

Inside is a rotor with six brass rings and a couple of decent little bearings, while the other half of the unit is a set of gold-plated spring contacts. There is extensive use of potting, and the verdict is that this is a surprisingly good quality component for the eBay price. We look forward to our community finding inventive uses for them. Having a ready-made unit sure beats making your own.

20 thoughts on “What’s In A Slip Ring?

  1. I’ve looked at these before, they seem.to be ok, especially for their price. But they are of limited use because there is no hole through them for an axle. They need to end mounted.

    1. You make a fair point, in this configuration without a hole as you say, you become somewhat reliant on the thing itself to be the axle, and reliant on its structural strength to fulfill that role.

      1. In one of my projects, I used a hallow shaft running through the bearing and mounted the slip ring assembly on the end of the shaft. So, no structural load on the slip ring.

        In another project, I used a “Lazy Susan” bearing that had a large enough hole in it for the slip ring assembly.

        Later, I replaced the slip ring with LEDs and photo-diodes using 2 different colors for the (2-way) data connection. The power connection still required a slip ring, but I was able to use a simpler, more robust one.

    2. Not really, though you do need big-ish bearings on either side of it. I have been using one of these (though with thicker wire) as a mains extension reel thing for the past 3 years, and my design puts no load on the slip ring at all. Just a bearing on either side.

    3. This is exactly why I bought a bit higher end of a slip ring. I tried using this thing as an axle. Ran it way over the speed ratings in the datasheet and all of the wires ripped right out of the slip ring. I knew I was running it out of spec but was impressed at how thoroughly it destroyed itself.

  2. I have quite mixed feelings with these.
    The plastic looks quite sturdy enough, but I don’t believe the bearings and the rest of the construction is intended for any other load then to hold the slipring construction itself together.

    Relying on some metal wires contacting a brass ring for the electrical contacts seem quite flimsy. It may be adequate for low power signals. I’m not sure about noise. A power bus can be buffered with a bulk capacitor on the other side, but for data, the amount of noise should be minimised. It looks like each wire is in a V-groove, and each contact has two wires, so that does make it unlikely that all 4 of those contacts will be open at the same time (due to some contamination, oxidization, etc).

    But the biggest problem with this is how long it will last. The wire construction may work for some time, but it does not look like it would last for many years. They look like they are adequate for toys. For robustness I have much more trust in the carbon brush based designs. They may be twice or thrice as expensive, but still a small part of the cost of most products. The carbon brush based designs often also have two brushes per contact to reduce intermittent contact during rotation (which also reduces wear though sparking).

  3. Jenny – I worked extensively with sliprings for a company that manufactures multi-axis robotic camera platforms for the TV and film industries.

    There are a few notable manufacturers – particularly, but not limited to China.

    Some sliprings can carry up to 48 low current (1 amp) conductors – they just keep adding stacks, so the length of the slipring grows in proportion.

    Some have co-axial connections for RF and video applications, others for ethernet, and some have optical fibre, for really high-bandwidth digital video (4K and 8K) applications.

    1. When Clive mentioned possible use for CCTV video sognals I assumed he was wrong because they’d do the video signal via WiFi and you only need the slipring for motors/power and IR filter activation.
      And in fact since most cameras only rotate a limited arc you could just use a flexible video cable to the camera itself. I mean when does a camera need to rortate so much that a cable with some slack won’t do? It would need to rotate for near or over 360 degrees

      1. There are many applications where a camera has to revolve a full 360 degrees, such as those fitted to the underside of media and police helicopters, and the cameras suspended on wires over a sports stadium.

        You will struggle to get good high definition video source images out of WiFi. The latency and dropouts would not be up to broadcast quality requirements.

        Most sports stadia use optical fiber for their 4k and 8k broadcast video sources.

  4. Very interesting engineering…. but…. the applications must be really super niche. I’d rather use Qi charging and wireless data if at all possible. Or, at the very least, I’d probably want to use all the lines on a slip ring for power to have redundancy for a little extra life, then make the data wireless.

    1. Slip rings are everywhere, what you you think the knob on your DMM is? Or even (sort of) a potentiometer?

      Not everything needs the latest & greatest tech, especial when it isn’t suitable. Good luck getting a few hundred watts thru QI, and wireless thru a foot of steel.

  5. LOL!

    I’ve worked in the ROV (Remotely Operated Vehicle) industry for some 40 years now. Sliprings are a constant in that arena, typically 2 per system. One topside, and one bottomside in the tether management system.

    Originally developed by Focal Technologies in Halifax, there are a number of manufacturers of these systems now.

    Just for laughs, the power transmitted is typically >3000 VAC down 9 conductors at ~15 amps each. Added to the fun is that nowadays multiple passes of fiber optic communications are included in the fray.

    The link to the Amazon S/R was pretty cool. I’ll forward that to a friend how uses small slip rings.


  6. These are commonly used on Astromech Droids like R2-D2 so that the dome can spin infinitely while most of the electronics can stay in the main body. The dome is mounted on a large lazy susan with a geared or friction drive.

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