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'[PIC] Design of a slip ring system (also known as '
2007\03\20@102331 by Thilo Klein

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Dear readers,

I want to design a slip ring system with concentric circles to
transmit 7 signals(ie 8 connectors). Do thou know a source(I prefer
books) which shows several methods of transmitting signals on rotating
elements ?!

Diameter of the outermost circle: 117 mm.

Diameter of the innermost circle: 81 mm.

Max voltage: 12V

Max current: 1A

The system is not very sensitive so there can be fluctuations(+- 0.2A,
+- 1V).

Regards

Thilo Klein

2007\03\20@115154 by Nigel Duckworth

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I did several channels of temperature information on a rotating flywheel
test rig for a former employer. This was battery powered and the
interface was 12 x 38KHz digital infra-red receivers arranged as points
on a clock face. The rotating transmitter used two infra-red LEDs spaced
at one third of the distance between two adjacent receivers. I used a
simple check sum for the data and had two error LEDs, one for no-receive
and one for checksum-error. I never witnessed the rig running but was
told it operated quite happily at 4000 RPM with little or no errors.

Regards,

Nigel        


Thilo Klein wrote:
{Quote hidden}

2007\03\20@121508 by Nigel Duckworth

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I've seen telemetry systems for measuring torque on prop-shafts which
are battery powered and use short-range RF. The transmitter is enclosed
in a plastic collar which clamps around the shaft and the receiver
antenna is a partial ring of brass of slightly larger diameter than the
collar.

Regards,

Nigel      


Thilo Klein wrote:
{Quote hidden}

2007\03\20@122333 by Bob Axtell

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Thilo Klein wrote:
{Quote hidden}

There are commercial slip ring assemblies, but they are VERY dear.

Personally, I believe one could design his own using custom beryllium
copper stampings and a precious-metal
PCB with circular traces.

Good luck.

--Bob

2007\03\20@135732 by Matt Bauman

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> There are commercial slip ring assemblies, but they are VERY dear.

I work in a university research lab, and we've purchased a few (some  
for many thousands).  If you're not looking for very high rpm/low  
torque/low noise, there are actually some reasonable assemblies out  
there.  Just a few months ago, we purchased a 12-channel assembly  
from Moog components (polysci.com) for about $150.  It's the AC6023,  
and is very compact; rated for 2A, 220VAC, and 250rpm.  We haven't  
used it extensively (yet), but it seems to work as prescribed.  It  
may be worth your while to give them a call -- they may have  
something for less than you can make on your own.

-Matt

2007\03\20@161741 by Peter P.

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Thilo Klein <ostentativ <at> arcor.de> writes:

> I want to design a slip ring system with concentric circles to
> transmit 7 signals(ie 8 connectors). Do thou know a source(I prefer
> books) which shows several methods of transmitting signals on rotating
> elements ?!
>
> Diameter of the outermost circle: 117 mm.
>
> Diameter of the innermost circle: 81 mm.
>
> Max voltage: 12V
>
> Max current: 1A

It is much easier to make a cylindrical transmitter (with eight copper rings
glued on a delrin tube pushed over the axle and use standard carbon brushes and
holders obtained as spare parts for an electric motor with the same diameter
collector as stator contacts).

For the 'disc' approach I have used four (or eight) pieces of model car race
track and the contact 'shoes' from the cars once. This is good for 4 wires and
1A and 12V as you need. The tracks are laid in a circle and glued on the moving
part (which was a spinning exhibit table in my case - so it did not need to be
very reliable or long lived). The shoes were glued on plastic rulers which were
each held by a bolt on the other side, so they could pivot. This took care of
any small eccentricity. A piece of rubber tube glued under the rulers provided
tension (very little is needed for car brushes).

Of course this is a toy.

hope this helps,
Peter


2007\03\20@202704 by Bob Axtell

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Peter P. wrote:
{Quote hidden}

That's how the slip rings on cable reels work. The brushes are
replaceable but if I remember right were not carbon
(but might've been carbon graphite, its been about 7 years since I was
in that industry). The reel did not turn very fast,
about 10RPM max.
{Quote hidden}

Good points, P.

--Bob

> hope this helps,
> Peter
>
>
>  

2007\03\21@081208 by Nigel Duckworth

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Hi Thilo,

I've only got time for a quick description and this is all from memory,
sorry.

The end user was measuring temperatures on the face of a rotating
flywheel using thermocouples so the transmitter was battery powered.

Transmitter
I signal conditioned the thermocouples using AD595s into a 10 or 12 bit
parallel A to D (can't remember which). This project was in the mid
nineties so I'm guessing I used a 16C84 or a 16C71, code was written in
CCS C.

The PIC scanned the temperatures, formatted a data-packet (split the
10/12 bit readings into two 8 bit values), calculated a checksum and
modulated a pair of IR LEDs at 38KHz via a transistor. Traditional
serial data protocol (RS232) was used which I must have done in code as
neither of the above PICs have UARTs.  

Receiver
I used 12 digital IR receivers with 38KHz filters then logically 'ored'
their outputs into a PIC interrupt and read the bit stream using code
(the IR receivers stripped out the 38KHz carrier leaving me just data).
   
The receiver checked the data for errors then latched it into DACs which
were then buffered and fed out to a chart recorder as analogue values.
As I said before I had two LEDs for 'checksum' and 'no-receive' errors.

As the temperatures changed relatively slowly I could tolerate a short
loss of data but as far as I know this didn't happen.

Hope this helps.

Regards,

Nigel




Thilo Klein wrote:
{Quote hidden}

2007\03\21@094613 by Nigel Duckworth

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Hi Thilo,

I was responding to the "several methods of transmitting signals on
rotating elements ?!" part of your request.

Can you give more details about your application, it sounds like you're
powering something more than signalling to/from it?

I'm not aware of any books on this subject, sorry.

Regards,

Nigel




Thilo Klein wrote:
{Quote hidden}

2007\03\21@171155 by Gerhard Fiedler

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Thilo Klein wrote:

> in my application I am driving a stepper motor and reading three variable
> resistors' values. These components are on a rotating table which
> rotates around 20 times in one direction with around 2 rpm. Then it
> turns around and rotates 20 circles back. This is already too much to
> connect a cable and to let it twist.

Maybe not... If you use a flat material (flex circuit) that you can wind to
a spiral and wind it 20 times, the additional 20 rotations only reduce the
diameter (to half of the original diameter, if you imagine all 20 or 40
windings on one diameter). This may be doable.

Gerhard

2007\03\21@191149 by Recon

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Thilo Klein wrote:

>Hello Nigel,
>
>  in my application I am driving a stepper motor and reading three
>  variable resistors' values. These components are on a rotating table
>  which rotates around 20 times in one direction with around 2 rpm.
>  Then it turns around and rotates 20 circles back. This is already
>  too much to connect a cable and to let it twist.
>  
>
I have worked brass and copper slip rings on different peices of
equipment.  Fair  rides, farm feed equipment  and others.   most of the
equipment was transferring  110 to 440 volt A.C.

If you are trying to read a resistance value through slip rings you
might have a problem with the resistance between your slip ring and
pick-up brush not being constant.

I know when the brush holder is designed it is built to go a certain
direction.  If you try to go the wrong way you have problems with brush
wear.

What kind of size are you talking about? shaft dia? how much space can
you allow for the slip ring?

Recon

2007\03\22@131228 by Jon Chandler

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We used a "home made" slip ring system for transferring data from hydro
turbine and other slow speed shafts.

The last project we did this on was interesting.  The turbine turned at
87 RPM, but the only place we could install a slip ring was a coupling
that was 7.5 FEET in diameter.  The slip ring was just a shade under 24
feet in circumference.

To make the slip ring, we used standard copper-clad PCB material and
mechanically removed copper to leave 4 tracks of about 1/2" width with
about 1/2" space between them.  Carbon brushes rode on each track.  We
transmitted power (low voltage DC) and a conditioned, multiplexed
signal.  We were measuring temperature, so we scanned each sensor for a
few seconds, with one reading set to zero to determine the starting
point of the sequence.  Worked really well despite our nightmares of the
slip ring assembly flying apart.

Jon

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