Slip Rings

Nice link, bookmarked for future reference.

Here is a pic of some much simpler slip rings I did on a project:

I haven't built any but I've cursed them a lot. I had to add four liquid level sensors onto a rotating print head with only a wildly fluctuating 80V supply to power them.

I would make them simple and easily repaired or replaced, for instance

3/4" copper pipe rings on turned-down 1/2" plastic pipe, or some other combination that leaves internal room for the wires around or within the axle. The rings would be wide enough for screws to attach them to the insulator and to fasten the wire to. Slip rings don't have to be perfectly round.

The brushes would be carbon for power and 3 or 4 redundant stainless wires for signal, with their own ground return, current limited in case the carbon brush fails. Their holders would be easily removed and adjusted for tension. On my Ford alternator there is a crosswise hole in the brush holder for a wire to hold the brushes off the slip rings during installation.

I'd send data with I2C or some other self-clocked, error-checking protocol and avoid DC control signals or sensor outputs on the rings, unless they were very tolerant of intermittent contact. Optical transmission works well when the shaft is turning and the rotation allows a simple serial to parallel converter.

Jim Wilkins

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> --Would like to hear from others that have been there/done that in

Slip rings are the easiest way to move power, but BlueTooth or ZigBee RF links can't be beat for data. Unlike optical, they work well in dirty environments.

I've seen some data acquisition systems on rotating machinery where the power was produced on the shaft via an 'inside-out' PM generator (fixed field magnets and coils on the shaft) to power all the electronics and the data was relayed back via an RF link.

cts. Da plan is

/done that in

I've repaired slip rings on automotive alternators with copper plumbing tubing. Automotive electrical brushes give very good life times for this material combination.

Turned off the old rings, and the insulator below to the ID of the Cu tube plus a few thou. Heated the tube and slipped on. After cooling turned the separate sections of the rings being careful not to cut through the wires and lugs.

New brushes of the correct hardness provided life of this assembly until the car rusted out. ('85 Hunday Pony of a neighbour's).

Replacement alternator brushes are cheap, or practically free at a scrap yard.

Wolfgang

I've only seen RF data links in commercial product development that required and had available expensive RF test equipment. Can you prototype and debug a Bluetooth type link with only an oscilloscope? I haven't found a cheap, functional spectrum or network analyzer yet.

The remote for my car operates at around 300MHz, which a good scope & probe will detect and display at close range.

Jim Wilkins