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'[ot]rotating sculpture tangled wire problem'
2002\07\12@055005 by sam woolf

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Hi everyone,
I've been designing the electronics for a rotating interactive sculpture.
There are two parts, a static base that acts as a turntable, and a revolving
pink blop that sits on top. The base contains a dc motor and mains
transformer. the top part contains a number of sensors (adapted from parking
sensors from http://www.velleman.be) that switch relays on and off when activated
to start the motor and change direction.

the problem is that wires between the revolving top-part and the static
bottom part get snagged and tangled as they are pulled round. There needs to
be two wires supplying power to the sensors and two wires from the sensors
to the relays. Can anyone suggest a solution to this problem... Surely
someone else must have encountered it before? I am imagining something like
rotating contacts but don;t know if these exist or what they'd be called if
they did. Or maybe I need to communicate wirelessly between the sensors and
the relays using RF?

Any suggestions much appreciated.

Sam.

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2002\07\12@085350 by Russell McMahon

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How much power (watts) do you want to transfer?

Inductive power transfer over distances of mm to a few cm is quite easy.
Do you want continual rotation capability or just say 360 degree rotation
maximum?


       Russell McMahon


{Original Message removed}

2002\07\12@100340 by Madhu Annapragada

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Slip rings.....although be warned that they are not very good for EMI
compliance.
Madhu

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2002\07\12@111937 by Francisco Ares

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Yes, there are rotating contacts, try a web serach to find them.

And, as this is a PIC related list, I'd put a PIC to read your sensors,
use three rotating contacts (power, ground common and serial
communication - RS232, maybe, for better noise rejection) and another
PIC to get the commands from the serial communication line and trigger
the relays.

Hope this helps
Francisco

sam woolf wrote:

{Quote hidden}

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2002\07\12@120319 by John Dammeyer

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Hi,

As an idea for coupling power up to the module that is turning you can
check out this link.

http://www.bobblick.com/techref/projects/propclock/propclock.html

It involves some motor modifications but is an excellent idea.
Communications with the upper turning portion could be RF but then of
course,  I'm slightly prejudiced there.

John


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Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

2002\07\12@134651 by Mike Singer

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Russell McMahon wrote:
> How much power (watts) do you want to transfer?
> Inductive power transfer over distances of mm
> to a few cm is quite easy.
> Do you want continual rotation capability or just
> say 360 degree rotation maximum?

  Navy guys have so-called "rotating transformers"
(translation from Russian). They have 2 ortogonal
windings on stator and 2 ortogonal windings on
rotor. May be used for AC 400 hz power transmission,
data transmission - varying frequency, determining
degree of rotation when rotating by simple motor,
also may be used as good rotating platform, as it
has strong bearings.

  Mike.
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  When responding, keep in mind, please,
this things may be under NDA.

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2002\07\12@140649 by H. Carl Ott

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Yes, a slipring would be the solution . You can buy (expensive) or try to
make your own. One possible cheap suggestion that works because you only
need 4 lines (and if your power requirements are low enough),  pick up one
of those inline gizmos to keep the cord to a phone handset untangled.

  Should only cost a couple of bucks, and should be readily available.

regards,
carl


At 09:47 AM 7/12/2002, you wrote:
{Quote hidden}

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2002\07\12@142109 by Francisco Ares

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This lokks like a very nifty solution! You may have some strong magnets
fixed to the motor case and some coils at the moving part, so you can
get a variable magnectic flux in the coils to get some alternating
current (how much?). And you can add something like a transponder to
send high frequency serial data ;-)

Francisco


Mike Singer wrote:

{Quote hidden}

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2002\07\12@155823 by Mike Singer

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  No magnets, just feeding stator coils (or windings - what
is correct in English?) with 400 hz AC. Rotor coils produce
secondary 400 hz AC to feed moving part's electronics.

  Mike.

Francisco Ares wrote:
{Quote hidden}

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2002\07\12@171632 by David Minkler

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Hi,
What Mike is describing is similar to a CT (control transformer) or a
synchro.  If your project is a one-up, these are regularly available on
e-bay.
Regards,
Dave

Mike Singer wrote:
{Quote hidden}

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2002\07\12@173401 by Kieren Johnstone

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OK, well if no-one will change it to "[OT]:" (which means its filtered out
for me), maybe "[EE]:", since its basically that anyway.

Or maybe I'm just hot and bothered today...

{Original Message removed}

2002\07\12@191659 by Andrew Errington

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Hi,

You could make a rotating slipring assembly with a jack plug and socket.
Depending on what the mechanical load is you can use the plug as the
pivot in the base, and the socket as the bearing and electrical
connection in the moving part.  You can get 4-way jack plugs, or if you
have a common ground then a three way (stereo) might suffice.  I would
suggest the 1/4" variety for strength, and I would imagine that this
construction would not last for long, but then, it might be ideal for
your application.

Andy

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2002\07\12@192544 by Jinx

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> You could make a rotating slipring assembly with a jack plug and socket.
>  Depending on what the mechanical load is you can use the plug as the

You could take some of the load off by using jockey wheels at the edge

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2002\07\12@215347 by Shawn Mulligan

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Filter [ot] as well, that's all.


>From: Kieren Johnstone <spam_OUTmisterfugitTakeThisOuTspamHOTMAIL.COM>
>Reply-To: pic microcontroller discussion list <.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU>
>To: PICLISTspamKILLspamMITVMA.MIT.EDU
>Subject: Re: [ot]rotating sculpture tangled wire problem
>Date: Fri, 12 Jul 2002 22:31:46 +0100
>
>OK, well if no-one will change it to "[OT]:" (which means its filtered out
>for me), maybe "[EE]:", since its basically that anyway.
>
>Or maybe I'm just hot and bothered today...
>

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2002\07\13@054246 by Roman Black

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David Minkler wrote:
>
> Hi,
> What Mike is describing is similar to a CT (control transformer) or a
> synchro.  If your project is a one-up, these are regularly available on
> e-bay.

Rotary transformer! Fantastic idea, every vhs VCR
head assembly has a rotary transformer and precision
bearings... I can just imagine the next wave of
propellor clocks... :o)
-Roman

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2002\07\13@075859 by Russell McMahon

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I'm pleased to see that after a longish digression into electromechanicals
(slip rings and ball bearings) we are starting to get back on track with
rotary transformers :-) (I mentioned inductive power transfer, Mike Singer
mentioned 400 Hz Russian military rotating transformers & Roman now mentions
video recorders).

Roman notes that all video recorders use rotary transformers in the heads -
something I was unaware of but it certainly makes sense. I assume this is
optimised for the several MHz video signal which is not a problem but I also
imagine the power that can be handled is very low.

So, I'll ask again -

       ????  How much power is this design meant to  ????
       ????  transfer to the rotating head?                    ????

The answer probably has a significant affect on which is the best. solution.

Inductive power transfer is not very hard - especially if high efficiency is
not absolutely essential. As an alternative to sliprings and their ilk it
has many advantages.




       Russell McMahon

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2002\07\13@094642 by Peter L. Peres
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On Sat, 13 Jul 2002, Roman Black wrote:

>David Minkler wrote:
>>
>> Hi,
>> What Mike is describing is similar to a CT (control transformer) or a
>> synchro.  If your project is a one-up, these are regularly available on
>> e-bay.
>
>Rotary transformer! Fantastic idea, every vhs VCR
>head assembly has a rotary transformer and precision
>bearings... I can just imagine the next wave of
>propellor clocks... :o)
>-Roman

You'd be hard pressed to pass enough power to light a LED with those.

Peter

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