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
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
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.
> --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
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
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.