Comprehensive Solutions for Every Application
Slip rings enable seamless rotation while transmitting power, signals, or data, solving the challenge of maintaining electrical connections in rotating systems. Electro-Miniatures delivers durable, precision-engineered solutions for the most demanding applications in defense, aerospace, and beyond.
Problem: “How can I get electricity to a continuously rotating part of my assembly? For example, if I want power available in a tank turret, how can I enable the turret to rotate without limits?”
Solution: “Use a sliding contact slip ring!”
How to Specify a Slip Ring
Specifying the right slip ring requires understanding its role within a larger mechanism and the environment it operates in. To ensure the design meets its intended application, consider the following key criteria:
Primary Design Criteria
- Physical Dimensions:
Include attachment arrangements and de-rotating features. - Circuit Requirements:
Detail the number of circuits, maximum current, and voltage. - Operating Environment:
Account for factors like temperature, humidity, salt fog, shock, and vibration.
Detailed Specifications
- Electrical Resistance:
Maximum resistance between rotor and stator, typically measured in milli-ohms. - Circuit Isolation:
Isolation between circuits, expressed in dB. - EMI Protection:
Isolation from external electromagnetic interference (EMI), also expressed in dB. - Torque Requirements:
Starting and running torque specifications. - Weight:
Define weight limitations for the assembly. - Data Circuit Descriptions:
Include specific data requirements.
Optional Features
Slip rings can incorporate additional components for enhanced functionality:
- Connectors
- Resolvers
- Encoders
- Fluid rotary unions
- Coax rotary unions
- Fiber optic rotary joints
At Electro-Miniatures, we help you define the exact criteria needed to create a slip ring design that meets your performance requirements and excels in its application. Let us guide you through the process to ensure precision and reliability.
Design, Integration, and Manufacturing Excellence
Capabilities Overview
Design
Design, Integration, and Manufacturing Excellence
Our design capabilities combine cutting-edge tools and decades of expertise to create slip ring solutions that meet the most complex requirements. From advanced modeling in SolidWorks and AutoCAD to innovative configurations like drum-in-drum designs, we ensure precision, reliability, and seamless integration into your systems.
Solid Works
Autocad
Proprietary design protocols for mechanics, electronics and metallurgy
Pioneered designs using a drum within a drum
Integration
Integrated Design for Advanced Systems
Today’s engineers face the challenge of designing smaller, lighter, and more cost-effective components while streamlining manufacturing and reducing overhead. Electro-Miniatures excels in integrating traditionally separate components—like motors, resolvers, encoders, and fiber optic rotary joints—into a single, efficient assembly. These innovations reduce housing size, weight, and the need for multiple bearings, simplifying system assembly and procurement.
With decades of expertise and access to top-tier suppliers, we specialize in custom solutions, including fluid-filled slip rings for deep-sea applications, EMI-isolated designs with Faraday cage housings, and EMI suppression filters for sensitive circuits. Let us help you achieve smarter, more efficient systems.
Insights
Dive Deeper into Slip Rings
This straightforward technique works in the frequency domain without the need for exotic test equipment to accurately find the distance to a fault in RF/microwave coaxial cables.
Great opportunity to learn more about the pioneer of slips rings.
No one seems to know who invented the sliding contact slip ring. The idea emerged from mists of the past like many ingenious things we take for granted…fire, the wheel, beer, domestication of animals and…slip rings. We know about Edison, the Wright brothers, (and their nemesis Curtiss,) Walter Reed and others whose inventions established whole industries. But what about that unsung hero who first passed current through a rotating surface?
When signals must pass rotating surfaces such as in security cameras, gun turrets and sensor gimbals, engineers often employ sliding contact slip rings to allow unlimited rotation. The trend is for more digital signals and more high density digital signals.
Slip rings seem to be one of the last considerations for systems designers, and for good reasons. Before serious work can begin on a slip ring design, the circuit requirements for the system must be finalized.
Read part of an interview about how slip rings were designed in radar systems.
Slip Ring History Series: Charles H. Smith, Slip Ring Pioneer
In 1916 Charles H. Smith published an in-depth article on brush technology (see our earlier article, “Brush Technology In 1916”) while employed by Westinghouse in Pittsburgh as, “Engineer of the Executive Department, and the Nation was my field of operation.” But before achieving that exalted position he was a poor country boy in Georgia. In an autobiography he wrote late in life for a family tree project, he lovingly describes his early education in a one room school house, recalling a classmate who was an ace at marbles and a blond girl who was his nemesis in spelling bees, whose nickname was ‘Cottonhead.’ Smith recalled that his teacher required students to pause as they entered the door and declare, “Bonjour, Madame,” as they entered, and “Bonsoir, Madame,” upon deperture; and that was the only French they learned!
Smith must have been an impressive young man. In 1888 at age 16 he became a messenger for the freight dispatcher of a small railroad. Abruptly and for no apparent reason he was told to pack his bag and begin studies at Auburn in September, 1889. He graduated at age 21 as part of the school’s first Electrical Engineering class. After a satisfactory temp job as an inspector with a Fire Insurance company, he was out of work for a while. Then an Auburn professor pulled some strings, and he was offered a position with Westinghouse in far-away Pittsburgh. After boasting of his good fortune, he reported in to discover his wage was 12 cents an hour and he was expected to work 54 hours a week! He worked and saved for months to buy a new pair of pants. After some time Smith won a raise to 16 cents an hour and became an apprentice to a “selfmade” construction engineer who taught him the importance of workmanship—the ‘extra touch—too often neglected’. After Westinghouse refused his request for 25 cents an hour, he accepted a job as Chief Electrical Inspector at the Cotton States Exposition in Atlanta ($75/month).
Odd jobs followed until the outbreak of the Spanish American War. Smith applied for a rank of Captain in an engineer regiment. He turned down an offer of 2nd Lieutenant. When asked if he would accept a commission as 1s Lieutenant, he agreed to consider it, and when it was formally offered, he accepted. In short order he was promoted to Captain and shipped out to Cienfuegos, Cuba. The War was already over, but Captain Smith worked on interesting projects there, including rehabilitation of a Spanish Army barracks for US Army use and laying out the camp site opposite Castillo de Jagua for occupation troops. Capt. Smith’s unit was “mustered out” on May 17, 1899, at Fort McPherson, Georgia.
After a few months he rejoined Westinghouse, where he served in engineering posts, including “District Engineer”, in St. Louis and New York City. In 1907 he returned to East Pittsburgh as Engineer of the Executive Department, where he wrote his learned article on brushes in 1916. When America entered World War I, Smith was granted leave to rejoin the Army Engineers. His commission as Major was delayed until January 28, 1918. At the age of 45 he reported to Camp Lee, Virginia, on May 5, 1918, for training. His first wartime assignment was at Fort Belvoir, Virginia, where he soon was assigned to the 20th Regiment of Engineers, “a skeleton outfit,” and then on to Camp Frement, California. There he selected a camp site for 170 officers and men who were due to arrive within 5 days. He was to have quarters and breakfast ready. He proudly reported that when they arrived two days early, quarters and breakfast were ready. This group was to have trained three new engineering regiments. But the Armistice occurred on November 11th, and the job at hand was mustering out. Smith became Camp Inspector for a 40,000 man troop area, where he quickly transformed the interiors of post buildings to expedite the discharging of men, a process that was “inexcusably slow.” Smith also administered claims by locals for property usage. But this work got interrupted when someone in Washington got him confused with another Smith, and he was abruptly discharged on January 6, 1919. He continued to refer to himself as Major Smith, even in his retirement.
After the War he returned to Westinghouse at East Pittsburgh, where he was again Engineer of the Executive Department, a position he held until he retired in 1938. He served as Director of the Westinghouse Club for twenty years, and he was elected President four times. This organization was both a social club and a technical education institution within Westinghouse.
During World War II Smith was a key manager of the construction of Ravenna Ordnance Plant and the Lake Ontario Ordnance Plant in Lewiston, NY. In July, 1943 Smith rejoined Westinghouse, where he was involved with “salvaging technical talent from the draft” and finally collecting data for a history of Westinghouse’ work during the War. After the War he retired. In his autobiography he complained, “the vicious, inane, and illogical practice of arbitrary retirement has precluded my further employment.”
Charles Smith’s expertise in slip ring brushes was part of a larger life as a practical engineer who took on challenges of many kinds wherever he found himself. Whether it was designing lighting circuits for expositions, establishing encampments on short notice, refurbishing electric locomotives for a mining operation, building ordnance plants to win WW II or leading The Westinghouse Club, Smith was a good man to have on the team.
Brush Technology in 1916
No one seems to know who invented the sliding contact slip ring. The idea emerged from mists of the past like many ingenious things we take for granted…fire, the wheel, beer, domestication of animals and…slip rings. We know about Edison, the Wright brothers, (and their nemesis Curtiss,) Walter Reed and others whose inventions established whole industries. But what about that unsung hero who first passed current through a rotating surface? With these things in mind I set out on a Google search to see what I could find. Of course the journey proved more interesting than the objective.
I soon found myself reading an article written in 1916 by Charles H. Smith, who at the time served as “Engineer, Executive Department,” of the Westinghouse Electric and Manufacturing Company of Pittsburgh, PA. The article was published in The Electric Journal, and the article’s title was, “Brushes For Commutators and Slip Rings, Their Selection, Application and Care.” The advanced technology of the day was carbon brushes, and Smith quoted brush manufacturers who said, “Carbon brushes were brought to the attention of the electrical profession in 1889, however, it was not until 1893 that this then radical departure in brush design met with any degree of success.” Recall this was an era when the country was rapidly adopting electricity and one can imagine the demand for power station generator equipment was strong. In 1916 Charles Smith was riding that wave.
A second quote Mr. Smith chose to introduce his article on brushes could have been made by an Electro-Miniatures design engineer today. Smith wrote:
The second [quote], not without justification, relegates excessive theory to the scrap heap in the following statement: “Abstract knowledge based on theoretical considerations offers little assistance in the solution of brush problems.”
The article offered an extensive discussion of the different brush materials available, along with their advantages and disadvantages. Lubrication was discussed along with the importance of cleaning up the debris they created. Smith pointed out the importance of proper brush alignment.
In a section on slip ring brushes Smith was critical of a new development of his time, the metal-graphite brush. He wrote:
In view of the doubtful virtues of the metal graphite brush, the apparently logical solution of the slip ring brush problem is the development of a graphite, or related, brush suitable for the purpose.”
Of course we now use very capable silver-graphite brushes with hard silver rings in many demanding applications. Smith seemed to be working with all copper rings in his day, and the ‘metal graphite’ brushes cut grooves in the copper. It was tough to envision the future back then, too!
Smith concluded his article with a detailed list of specifications to provide a manufacturer when ordering brushes. He ended with two maxims that wise slip ring customers should adopt today:
- “From the above it must be concluded that if what is wanted is expected it must be made clear what is wanted.”
- “… requirements are in no sense stable. It is wise, therefore, to encourage a receptive disposition and to be ready for such advances in the art as may seem worth while
In a future Note I will review highlights of Charles H. Smith’s career, from his first job with Westinghouse at $.16 an hour to his trip to Cuba as an Army Officer in the Spanish American War.
Slip Ring Considerations For High Speed Signals
When signals must pass rotating surfaces such as in security cameras, gun turrets and sensor gimbals, engineers often employ sliding contact slip rings to allow unlimited rotation. The trend is for more digital signals and more high density digital signals. Today’s ‘vetronics’ suite for armored vehicles, for example, increasingly requires higher speed digital signals to support Ethernet communications and better images from sensors. Slip rings must provide the interface of these signals between the vehicle hull and the turret. Sliding contact slip rings have limitations for passing these new signals. What limits and options does this leave the system designer? What are the design trades? What are the cost impacts?
Maintaining signal integrity
Before addressing the trades, let’s address a more fundamental question. What are the fundamental challenges to passing high frequency signals through sliding contact slip rings?
- Impedance matching:
High frequency signals are passed over coaxial cable (typically 50 or 75 Ω) or twisted pair cable (typically 110 Ω). For best fidelity, this impedance level must be maintained over the length of the cable. The cable impedance (measured in ohms, denoted by Ω) is determined by the materials used and by the physical dimensions of the cable. However, a slip ring intrinsically violates both of these constraints: its geometry and materials used are very different from those of cable. Therefore, special care must be exercised in the design and manufacture of a slip ring to be used for high frequencies so as to cause the least disruption to the system impedance level. - Signal path:
Signals travel around the rotor in both clockwise and counterclockwise directions. While for low frequency signals this path difference is negligible, at high frequencies it is not. Depending on the position of the rotor relative to the stator, these distances will not be equal, resulting in varying signal distortion as the joint is rotated. For high frequency signals, the rotor diameter (and hence the path lengths) must be kept small. Depending on the mechanical constraints of the system, the rotor may have a section of smaller diameter to accommodate such signals. - Crosstalk
At high frequencies, signals are not bound by insulation and electromagnetically travel from conductor to conductor. Thus, the signal on one circuit may interfere with that of a neighboring circuit. Careful design of the slip ring can minimize this interference, bringing it to a low enough level that it will not cause problems in the system. - EMI shielding
Often it is necessary to ensure that a signal does not radiate from its cable and/or is not susceptible to external electromagnetic radiation. For this reason, system designers use shielded cable, which has a grounded braid surrounding the conductor. This shielding is interrupted when the signal must pass through a slip ring. Careful design techniques are used to ensure shielding integrity while the signal is passing through the slip ring. - Noise
Because a slip ring contains sliding contacts, a certain amount of noise will be introduced as the brush passes over microscopic imperfections in the rotor. The noise can be mitigated by adjusting the brush pressure and by the use of multiple contacts on each ring.
Summary of things to consider when specifying a slip ring to be used for high frequencies
- What are the frequencies that must be transmitted through each circuit?
- Which signals must be isolated from others? What is acceptable crosstalk?
- What are the EMI shielding requirements?
- What are the rotational noise constraints?
The hardest part in designing a slip ring for your system is properly determining its requirements. Requirements that are too stringent result in overly complex and expensive products; if too lax they can result in unpleasant surprises when trying to integrate the slip ring into your system. Specifying a slip ring is most successful when there is a dialog between the customer and the slip ring manufacturer, negotiating between what is desired and what is practical, separating the “must haves” from the “it would be nice if’s…”.
The most important decision for a slip ring design project is the choice of the slip ring vendor to recruit onto the system team. Electro-Miniatures Corp. brings over 50 years of design experience, a solid record of successful designs delivered on time and produced to the highest quality standards. You can make your slip ring program successful by joining BAE, Lockheed Martin, Raytheon, Northrop Grumman and L-3 and make Electro-Miniatures Corp. part of your design team.
Introduction To Slip Ring Trades
Slip rings seem to be one of the last considerations for systems designers, and for good reasons. Before serious work can begin on a slip ring design, the circuit requirements for the system must be finalized. In an ideal world the system design should allow sufficient space of a convenient shape to accommodate the slip ring and cable harnesses to the rotor and stator. Somewhere along the path to a final design concept the systems design team and the slip ring specialists should confer to establish the slip ring design concept to meet the circuit requirements within the space available. Here is a list of trades and other considerations that should help advance this process to a happy conclusion:
- Power, Voltage and Current. Designers should recognize that current requires copper and voltage requires space. When amps go up there is no alternative to increasing the cross section of copper in the wire and beefing up other components to control heat generation. At the same time when voltage increases there is a need for increased isolation, and this usually means more distance between circuits and more space for the slip ring.
- Shape. In general additional length is more useful to a slip ring designer than additional diameter. Length can often be shortened by using an inner and outer slip ring (an approach pioneered by Electro-Miniatures), but this is more costly than a single long slip ring.
- Compactness vs Manufacturability and Cost. There is often pressure on the systems people, especially for airborne systems, to drive size and weight as small and light as possible. But this comes at the expense of manufacturability. The effect of making slip rings more difficult to manufacture is to make them more expensive.
- Isolation. The more compact the slip ring, the tougher it is to achieve circuit isolation goals.
- Connector Selection. It seems there should be potential for cost and lead time savings by selecting common connectors used in industry rather than trying to optimize space utilization with a custom or rarely used connector. Lead times tend to be less for commonly used connectors, too.
- Sealing vs. Torque. Some applications must operate in harsh environments that require the rotating seal to be tight. Other applications, especially where the slip ring is part of an accurate aiming device, demand that the slip ring offer low resistance torque. Systems designers should be aware that there is a trade between torque and the degree of sealing. It is tough to optimize the seal and provide the lowest torque in the same unit.
- Housing Material. Most slip ring assemblies for defense applications use aluminum housings. Aluminum is strong, inexpensive, easy to machine, relatively light, conducts electricity and provides the basis for a Faraday Cage, if required. If weight is critical, then titanium can be used. Titanium is expensive and harder to machine. For applications in corrosive environments the housing can be made from stainless steel. This adds weight and cost.
Since the introduction of the Sequestration budget and DoD’s “Better Buying Power” guidelines, there has been increased demands from defense customers for suppliers to offer alternatives to the RFP specification that could save the Government money and have negligible impact on performance. This new era of procurement will be a challenge, requiring engineers to consider alternative designs and understand cost impacts of their choices.
We hope this summary of slip ring trades will help you to shape your thoughts on your next slip ring design project. Contact us for help with your slip ring design challenges.
Early Radar Slip Rings
From Rutgers Oral History Archives.
Jared Kosch: This begins an interview with Robert H. Zeliff, Class of 1943, on May 17, 2003.
[Much material skipped.]JK: What were your feelings on being involved in radar in its early days and its use in World War II? Can you give me a little background as to how radar came into being in this time and its significance, possibly, in the attack on Pearl Harbor, as well as its significance generally throughout the war?
RZ: No, I’m hardly an expert on that, but the radar really, in its practical infancy, was developed in England, and all of our people that got into radar, in their early training, had to go to England to get it, because that’s where the knowledge was. So, what we picked up to get our radar program starting just grew out of the development that was really going on in England. … To my knowledge, the first two radars that were developed that were put into, you know, mass use by our forces were the SCR-268 and the SCR-270. SCR, incidentally, it was “Signal Corps Radio;” they didn’t even have a name for it, and so, … they had numbers, just like a radio did, but it was [radar]. … The 268 was a searchlight-control radar, because that was the first application, was to try to help to steer searchlights, and the SCR-270 was the first long-range search radar and that was the one that was employed in Oahu at the time of Pearl Harbor, but, again, this was such a new device that the “old guard” officer corps had no real confidence in it at all and they just thought it was a new toy that they were playing with, I think. I think that’s pretty much the story. I’m not, of course, conversant on anything first-hand, but … there’s no question about it, that the radar was active that morning and did pick up the Japanese flight coming in, but, essentially, what it amounts to is, they couldn’t get anybody to believe that, you know, what it could possibly have been, and, again, I guess, because nobody had really understood, you know, the tactical significance of this new toy. Of course, the things quickly changed and, like everything else, the radar program blossomed very quickly after, after World War II [developed] and special radars were developed for the Navy, which were different than the ones that developed for the Army. I’d mentioned the SCR-584, which is the other one I was trained on and did some instructing [on]. Now, that was a radar that was used for gun laying, for directing fire of antiaircraft artillery. … 584 was used extensively during the war and was used for, I’ve seen them in the field in other countries, because we gave some of them, I think, to the Russians and, somehow or another, some of them got in Chinese hands, and I think I’ve seen them used, like, thirty, forty years after the war was over. It was a very successful radar. It was ten-centimeter radar, shortwave radar, that had a long life, yes, and, as I say, radar today, I would hesitate even to talk about it, because it has advanced way beyond any experience I had with it. So, it’s not the same animal, but a derivative from the same technology. I mean, you can see that, you know, if you follow the development of radar, how it was an evolutionary process and started out from one common base. Interesting little story about this; the English developed [a system that] had their radars where the operator would sit on the pedestal that the antenna was on. So, if it was an antenna that was a rotating antenna, … to track aircraft, the operating hood, that would rotate around with the antenna. … When we first started to develop our rotating ones, we had, we called it “slip rings,” where we could make electrical contact with the radar, but with the operator staying fixed. … Again, the English were one of the first ones that developed automatic tracking radars, where you could lock on to a target and, without the operator doing anything, … you could get it to follow the radar, I mean, the radar to follow, track, the target, but, in the early ones they developed over there, and, of course, they had the same business where they would go around with the antenna; … they started off, they put one of their first prototypes in Hyde Park in London. …
————————————–END OF TAPE ONE, SIDE ONE————————————–
RZ: When they first picked up a flight of incoming [aircraft], a German flight, they’d be about a hundred miles out and, at that distance, a group of planes just looked like one target, but, as they got closer, then, you could start to see the individual airplanes would start to show up on the screen. … Of course, this device, attempting to lock on a target, couldn’t figure out which one, when they start [breaking up], one started to become many, which one to lock on. So, these [radar], this antenna would bounce around [laughter] and the operators in it would be bouncing around, they’d be flying off the walls, until they figured out, … for that, they had to figure out a little different way [of] how to handle that problem. I think that probably [is] what got the development of the slip rings going, I guess, [laughter] when they started bouncing operators off the wall … on these automatic tracking radars, but, oh, I would venture to say there are probably a thousand stories, you know, semi-comical, … in the early days of many inventions, as that one always, always made me laugh.
