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I am curious about using a rolling element bearing (several) to deliver either signals, processing power, or even drive power to a rotating shaft.

As I understand, all bearing manufacturers discuss mechanical damage to bearings that are transmitting spurious currents through erosion, something like EDM (electric discharge machining).

In this case, the machine's loaded bearings are seeing unmanaged induced currents to ground or some other thing. The mechanism seems to be that the grease insulating layer is broken down by the potential, and an arc is what is causing the damage.

I am imagining a system where the bearing's entire job is to transmit electrical current so run essentially unloaded, and potentially 'dry', to ensure good electrical contact, perhaps with a spring preload to maintain contact.

Has anyone attempted such a thing with any level of success? Is there significant resistance to power transmission? Is there noise on signal lines?

  • Acoustic noise is not an issue
  • Data is nominally analog but could be digitised over the right protocol.
  • Maximum power 500W DC.

Edit: Ideas summary

  • Graphite lubrication
  • Optical digital signals
  • Inductive processing power
  • Electrically conductive grease
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    Mar 2 at 18:21
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3 Answers 3

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Reliable attempts to electrically bridge a rotating element often require extraordinary effort. One example is a variable capacitor, where rotating plates interact with fixed plates: a low-resistance path to rotating plates is required.

This military capacitor was used in a 100W transmitter, where considerable radio-frequency power was present. It operated over extreme temperature range, in a very high-vibration environment, circa 1940.
One rotating shaft end is suspended by un-lubricated ball bearings. No doubt, some electrical current could flow across.
However, the main electrical path was carried at the other shaft end, via a silver-plated spring-loaded wiping contact. This capacitor was not meant for constantly-rotating service...I doubt the silver plate would last. Without this wiping contact, I've seen a variable capacitor fail in a far-less severe environment. This approach seems common for intermittently-rotating service.military capacitor photo

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The ISS uses roll rings (rolling flexures that transfer electrical power through a rotating joint), as an alternative to slip rings. You can find papers on the implementation. They are suitable both for high current and for low-noise signals.

In a system I worked on we used inductive power transfer and optical data transmission (RF could have been a possibility in another situation), but that was mostly because we needed to keep the friction to almost zero. It used air bearings which don't provide an electrical contact.

Another possibility which works in some situations is to use optical, RF or inductive data transfer and to use batteries for power.

Non-conductive (eg. ceramic) bearings are available (or the bearings themselves could be insulated from the surrounding structure) in order to restrict current flow to the desired path(s).

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    \$\begingroup\$ I wonder how they avoid vacuum welding. \$\endgroup\$
    – DKNguyen
    Mar 1 at 16:46
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    \$\begingroup\$ @DKNguyen, the solar alpha joints are in continuous motion, and I'm fairly sure the radiator joints are too. That leaves only the solar beta joints, which are adjusted frequently but not continuously. \$\endgroup\$
    – Mark
    Mar 1 at 23:25
  • \$\begingroup\$ I like the NASA solution here, the rings appear to allow the bearing to deform and increase the surface area of contact. I wonder if these are all bespoke if any manufacturer makes them as a standard fitment part. \$\endgroup\$
    – J Collins
    Mar 7 at 12:49
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Maybe whatever scheme you come up with will work, maybe it won't. The issue will be that even if it "works", you don't know any of the specs -- how much current it could carry, how much noise you'll introduce, how long it's likely to work for, ....

So if you're doing something important or risky, you'll need to spend effort and time to validate whatever approach you want to take.

I suppose you can do this, but the more cost effective option would be to use the element designed for such uses -- slip rings -- and spec out the right set of slip rings to do the job right.

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