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Electronics on a rotating platform

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m1tch37

New Member
I am required to build a 360 degree proximity sensor. I plan to use a ultrasonic range finder on a constantly rotating servo.

The problem I am having at the moment is how do I wire the sensor without it tangling and twisting up.

Its a simple, stupid problem, but I cant work out a practice way to attach 3 wires to a rotating platform.

Any ideas?

Thanks
Mitch
 

ericgibbs

Well-Known Member
Most Helpful Member
I am required to build a 360 degree proximity sensor. I plan to use a ultrasonic range finder on a constantly rotating servo.

The problem I am having at the moment is how do I wire the sensor without it tangling and twisting up.

Its a simple, stupid problem, but I cant work out a practice way to attach 3 wires to a rotating platform.

Any ideas?

Thanks
Mitch
hi,
A simple way is to use 'slip rings' on the platform shaft.
 

m1tch37

New Member
Thanks Eric, I just needed to know the jargon

Edit: I am having a hard time finding slip rings in small quantities and something that would nicely fit a servo. What would a good retailer be?
 
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ericgibbs

Well-Known Member
Most Helpful Member
Thanks Eric, I just needed to know the jargon
hi,
The signals/power passing thru the slip rings will determine the type/rating of the contacts.

Its possible to make home made light duty slip rings, using copper as the 'ring' and the wiping contacts,
using the screening braid from screened cable.
The braid is kept in tension by light springs, wiping an arc of about 120 degrees.
Space the wipers 120 degrees apart around the shaft in order to even out the 'pull' on the shaft.
 
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m1tch37

New Member
I am considering something like that, they dont appear something easily available to the DIY market.
 

ericgibbs

Well-Known Member
Most Helpful Member
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Mikebits

Well-Known Member
Hey, that is real slick. I ran across a similar problem sometime back when I built a wind speed/direction measuring device, but I could not remember what I did. Cool link thanks. I think I will bookmark it, but I have so many bookmarks now, I will never be able to find it again. :(
 

m1tch37

New Member
Thats a real nice approach I agree. Unless you drilled a hole all the way through the servo (?) I don't see how that could work unfortunately. The first website was helpful and i have some ideas of my own.

I was thinking of having a few conductive rings on the bottom of the platform and bend metal strips onto it. As the platform rotates, conductivity is maintained on the 3 rings.

I might just have to experiment.

Edit: Just like the audio jack, I found a nice solution similar. A google search for phone cable detangler gives 100s of slip rings with RJ11 connectors. Like: http://www.shopping.com/xPO-Softalk-SOF03215-Softalk-Tangle-Free-Telephonetwisstop-Cords

I might be able to work with one of them.
 
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RadioRon

Well-Known Member
I recently found that the steering wheel in a car uses slip rings to carry control lines out to the buttons on the wheel. Older ones just have one slip ring for the horn, but I wonder if there are more than one slip ring in newer ones. Perhaps a visit to the auto wrecker might be interesting.
 

Boncuk

New Member
Here's my suggestion, easy to build and always proper and reliable function.

Make a double sided PCB (70µm copper layer for longer life, normally 35µm). Take one of those pins holding the bracelet of of a wrist watch. (Sorry, don't know the exact term)

It is a hollow steel bar with two small solid bars inside which are spring loaded.

Cut that part into two equal pieces using a dremel. Do it with caution because the spring will pop out eventually. Cut the spring in two halves too and shorten for minimim pressure. Insert the solid bar into 1/2 pipe followed by the adapted spring. Close the hole with a suitable piece of copper wire and solder the copper and the hollow steel bar together (it should be stainless steel, easy to solder) for mechanical strength. The stroke of the small steel bar is 0.5 to 0.7mm which will compensate for a slightly tumbling movement of the disc.

Use a second piece of PBC material and solder the contactors in place. Solder the connections on the rotating disc using through contacting. Make sure the contactor is absolutely smooth and ball shaped (ball shaped for self cleaning). Sharp edges will cut a groove in the PCB copper layer very quickly.

That way I've made measuring clips for for screw terminals to contact three terminals simultaneously.

For clarity take a look at the small Eagle sketch.

Hans
 

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The Mad Professor

New Member
As a quick build solution I would go for the 1/4'' jack plug and socket route and look at sourcing a captive bearing to go around it and take the load from above once the prototype functioned as required.

Wild guess here... is this part of an Automated Sentry Gun project ;)
 

m1tch37

New Member
Thanks for your long response Boncuk. I have decided to use a audio cable (or similar) and pass it through a through-bore servo I have. It will work well.

My question now is, what cable should I use? I obviously want one that can rotate like a audio cable, RCA cable or DC power jack, however I would ideally like 4 wires (I can do with 3 if i must) and for it to be as thin as possible. I am not having much luck with my usual suppliers, could anyone give me a hand?

Edit: What about the iPhone headsets? That would be perfect. I will just get one of the adapters made to fix the recessed iPhone jack and use that. I wonder how many channels it has? Will be atleast 3 i guess.
 
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Boncuk

New Member
Hi,

your'e not going to salvage an I-phone headset for a piece of cable, are you?

Check with your local radio-TV-shop for a suitable cable. Combined record/replay audio cables usually have four wires + shielding. They are pretty flexible.

One meter of that cable shouldn't cost more than a dollar.

Hans
 

Externet

Well-Known Member
Hey Mitch... the 99¢ store sells packs of 3 AT&T slip ring contacts used in RJ22 telephone handset cables, I bought a pack today. As the current you need is not too high for a proximity detector, it is worth implementing the thinghy. RadioShack has them too at 15 times the price if you prefer.
I have it in my hand now, says part #91078 at www.telephones.att.com
The beauty is you can use already made handset cords with it.

Miguel
 
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Diver300

Well-Known Member
Most Helpful Member
You could use one of the rotary transformers from a video recorder. (VCR)

The heads on a video recorder spin to give the helical track, and they are fed with a rotary transformer inside the head drum. The bearings are already there for you.
 

jbeng

Member
Have you considered not moving the electronics at all? Use a concept similar to the one used in rotating police beacons, where a reflector directs the beam and the lamp does not move. It would negate the need for any power or signal transmission via slip rings.

In this case, use a motor to rotate a 45-degree reflector mounted above (or below) a stationary transducer.

Jeff
 

Krumlink

New Member
Here's an idea that would be pretty easy:


It would require a piece of copper pipe cut into a thin piece (quarter inch) and put a commutator on it.
 

mvs sarma

Well-Known Member
How about trying Radio link(433.92MHz pr some approved frequency for the area) to the rotating platform, imagining that the power supply is there atop.
 
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