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Q: How send electrical signal through spinning shaft ( Answered 5 out of 5 stars,   2 Comments )
Subject: How send electrical signal through spinning shaft
Category: Miscellaneous
Asked by: questionsly-ga
List Price: $25.00
Posted: 10 Mar 2006 09:58 PST
Expires: 09 Apr 2006 10:58 PDT
Question ID: 705769
What are the most common ways in industry to send an electrical signal
down the length of a spinning shaft?  It would seem that a wire would
get tangled up in the spinning shaft.
Subject: Re: How send electrical signal through spinning shaft
Answered By: byrd-ga on 10 Mar 2006 19:06 PST
Rated:5 out of 5 stars
Hello questionsly-ga,

The most common way in which industry solves the problem of sending an
electrical signal down a spinning shaft is by the use of a device
called a ?slip ring.? This is defined as ?an electromechanical device
that allows the transmission of power and electrical signals from a
stationary to a rotating structure.? In your question about a spinning
shaft, the slip ring assembly would consist of the spinning shaft, and
a stationary conductive ring (or sometimes disk) with metal or
graphite brushes (contacts) mounted on it, which rub the shaft and
transfer electrical signal or current to it. However, in other
instances, it is the shaft which remains stationary, while the slip
ring spins around it. Either way, the principle is that part of the
assembly spins, while part remains stationary.

This design is still the standard used in industry, and there are many
thousands of sizes and designs of slip rings, which range from very
tiny fractions of an inch to several feet in diameter, for thousands
of applications from microtechnology to aerospace. However, although
slip rings are fairly simple devices, they are prone to some problems,
which include wear, oxidation, high electrical resistance, and a high
degree of electrical noise. As a result there have been and are
ongoing efforts to improve traditional slip rings and to invent new
devices that will perform the same function while eliminating, or at
least reducing, the drawbacks of slip rings. Some of the names of
these devices are interchangeable with ?slip rings,? while other
indicate a different type of device altogether. These include:

mercury rotating connector
pancake slip ring
rotary band contact
rotary power transfer device
rotary transformer
rotating continuity device
rotating electrical connector

Following is a list of resources that will further explain and
illustrate the construction, operation and use of slip rings, and
answer some common questions.


This article from United Equipment Accessories, Inc. is slanted, of
course, toward this company?s own products, but it gives a very
detailed, nicely illustrated explanation of what slip rings are, how
they?re made, what they?re made of, and examples of some common uses.
In addition, this company has a nice Flash animation showing how a
slip ring works (scroll down a bit to see the link): 

This is a brief overview of slip rings from Airflyte Electronics, on
manufacturer. It?s short, clear and to the point.  
?BASIC SLIP RING DESIGN? on the same site further expands on this, and
has links to detailed explanations of each aspect of slip rings,
including electrical, mechanical, environmental conditions, and
special problems. 

Moog Components Group has some excellent information on slip rings,
and an interesting FAQ, which answers such questions as ?A slip ring
seems to be called a lot of different names - rotary electrical
interface, commutator, collector, swivel, and rotary joint are a few
that I've heard. If they're all the same thing, why are so many names
used? I wish you guys would make up your minds - it's confusing!? 

Wikipedia has a nice short article about slip rings,  here; 

Progressive Engineering of India provides a good FAQ about Rotating
Electrical Connectors, with an animated gif showing one in action:  

A Scottish company, Bowtech Products, Ltd., has some interesting
diagrams illustrating several different ways of mounting slip rings on
this page:  


Some variations on the basic slip ring include:

The Mercotec ?Rotating Electrical Connector? uses an electrical
connection ?made through a pool of liquid metal molecularly bonded to
the contact? instead of the typical brushes. Here?s an interesting FAQ
about their design: 

Honeybee Robotics has designed a ?Brushless Slip Ring? (aka ?Rotary
Band Contact?) that uses rolling contacts to transfer the electrical
signal as opposed to the more common sliding brush type contacts.
Here?s a description of their product, with a photo:

Probably the newest type of connector is the ?Contactless Magnetic
Slip Ring? which was developed by NASA?s Ames Research Center.  It is
not yet commercially available, but you can read about it here:   


Following are links to some of the companies making and selling slip
rings and rotary connectors of various types. Some, like Moog for
instance, have product lists or catalogs with literally thousands of
different designs, and most will also design custom slip rings to spec
for specialized use. All have diagrams, photos, specifications and
lots of interesting information about their products in particular,
and slip rings/rotating electrical connectors in general.


FABRICAST, El Monte, California   


MOOG COMPONENTS GROUP, headquartered in Blacksburg, VA, with offices
in North Carolina, Pennsylvania, Canada, England  
Moog?s catalog of over 6,000 slipring designs): 

Rotary Systems, Inc., Minneapolis, MN 


Simple slip rings:  
Complex slip rings: 

TECHTRON CORPORATION of Naples, FL and Signal Hill, CA   


I hope this information fully answers your question and gives you some
good resource material for learning more about how to get electrical
signal down a spinning shaft without tangling up all the wires. If
not, or if anything isn?t clear, please use the ?Request for
Clarification? feature to ask before rating and closing your question.
I want to be sure you have the answer you wanted and the information
you need. Also, despite care taken, sometimes links don't post
properly, so if you have trouble with any, let me know via RFC and I
can try to repost any difficult ones. Thanks for an interesting hunt!

Best wishes,

Search strategy:

I began by asking an electrical engineer of my acquaintance your
question. His immediate answer was ?slip rings,? which he briefly
described, and which I then used as a basis for further research.

To locate resources and information, I used the following search
terms, which you might like to use also if you?re interested in
locating additional material:

[slip rings]
["slip ring" OR "slip rings" OR sliprings OR "slip ring assemblies" OR
"rotating electrical connectors"]
[?what is a slip ring?]
[?how does a slip ring work?]
[?slip ring? consists of]
[types electrical connectors "slip rings" OR rotary OR rotating]
[electrical connectors rotary OR rotating]
[manufacturer ?slip rings?]

Clarification of Answer by byrd-ga on 11 Mar 2006 05:19 PST
Hi questionsly-ga,

Kottekoe-ga has posted an interesting comment about wireless signal
transmission that I thought would be good to expand upon a bit. I
didn't include mention of this technology in my initial answer because
it isn't commonly used in industry for the purpose you were asking
about, i.e. sending an electrical signal down a spinning shaft.
Rather, these types of devices, known as ?Rotary Joints,? e.g. Fiber
Optic Rotary Joints (FORJ), Microwave Rotary Joints, RF Rotary Joints,
and/or Radar Rotary Couplers, are more often used for sending digital
signals for data transmission rather than electrical signals for power
transmission, though also sometimes used for the latter.

But Moog Component Groups, which manufactures these as well as slip
rings, says, ?(FORJs) are to optical signals what electrical slip
rings are to electrical signals, a means to pass signals across
rotating interfaces, particularly when transmitting large amounts of
data.? Therefore, a frequent use for such devices is in
telecommunications, with other common applications including robotics,
ROVs, radar antennas and security systems.

In fact, these types of devices are frequently used, not necessarily
as a replacement for conventional slip rings, but in addition to and
integrated with them as part of a larger assembly. In these types of
situations, the optical or microwave/RF devices carry data, while the
conventional or modified slip rings handle the electrical power.

If you?re interested in exploring this technology further, here are a
few links for you:

?Fiber Optic Rotary Joints (FORJ)? (Moog Components Group):

?Tutorial: Fiber Optic Rotary Joints? (Princetel):

?Rotary Joints? ? A technical description of various types of
contactless rotary joints. (Sivers Lab) 

Integration of FORJ with Slip Rings (Princetel):


Most of the manufacturers listed in the first part of this answer also
make rotary joints. In addition, here are a few others who specialize
in this area:

Microwave Rotary Joints 

KEVLIN CORPORATION, Methuen, MA (a division of Chelton Microwave Corp.
under Chelton Group, hdq. in Lewisville, TX)
Microwave Rotary Joints 


Radar Rotary Couplers, Microwave Rotary Joints

I hope this additional information helps you better understand the
types of technology that enable data and electrical signals to be sent
to spinning or moving parts. In locating this information, I used the
following search terms:

["rotary joints" "fiber optic" OR microwave OR RF]
[FAQ "rotary joints" "fiber optic" OR microwave OR RF]
[manufacturers "rotary joints" "fiber optic" OR microwave OR RF]

As before, please use the ?Request for Clarification? feature to ask
if any thing isn?t clear.

questionsly-ga rated this answer:5 out of 5 stars
Nothing to add, you guys are great

Subject: Re: How send electrical signal through spinning shaft
From: kottekoe-ga on 10 Mar 2006 21:07 PST
Another method that involves no potentially unreliable sliding
contacts is to use a wireless link that could use optical or radio
frequency communications. This is especially useful if the signal to
be transmitted is in digital form. The digital signal is transmitted
wirelessly from the spinning element to the stationary one or vice
versa. One issue with these methods is finding a way to transmit the
power to the moving side of the link. The easiest way to do this is
with a battery, but you can also couple the power inductively or
Subject: Re: How send electrical signal through spinning shaft
From: byrd-ga on 16 Mar 2006 05:13 PST
Dear questionsly-ga,

Thank you very much for the kind words and five stars! I'm really
happy you're pleased!

Best regards,

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