Servotecnica Slip Ring Spotlights: Understanding the Differences Between Slip Ring Types with Sara Giussani

Q: Sara, when engineers approach you about slip rings, what is usually driving the conversation?

 A: Most of the time, they come to us because they need to transfer electric power and signals from a fix structure to a rotating one. The real question is how to integrate that rotation into their machine without creating long term reliability issues. That’s where the type of slip ring becomes important.

The choice is rarely just electrical. It’s mechanical, environmental, and functional at the same time. The geometry of the machine, the mix of power and signals, the operating conditions, and even service access all influence which solution makes sense.

Q: If someone were to ask for “the differences” between capsule, through bore, flat and fibre optic slip rings. What’s your simplest way to frame it?

A: I use two questions.
First: What does the mechanics demand? Capsule and through bore are “drum” geometries, flat is a pancake style geometry that trades diameter for reduced height, and through bore exists specifically because many applications need to mount the slip ring on the machine shaft.

Second: What does the transmission demand? If you are mainly transferring electrical power and standard signals, an electrical slip ring is typically the right tool. If the requirement is optical data transmission through continuous rotation, driven by bandwidth and EMI considerations, then a fibre optic rotary joint (FORJ) becomes the only choice.

Q: Let’s talk capsule first. What defines a capsule slip ring in practical terms?

 A: Capsule is the option I reach for when the design needs to stay compact and cylindrical, and when the goal is mainly to transfer a high number of signals in a small envelope.

In the Servotecnica catalogue, SVTS A is positioned around compactness, high circuit density and optimising signal transmission. The family is explicitly described as supporting low noise and reduced interference between circuits, with gold contact technology used for signal quality, including high data rate and high frequency signal transmission.

 From an application perspective, SVTS A is shown in use cases that are very familiar to engineers: video and control systems, medical and pharmaceutical equipment, packaging, small wind turbines and cable reels, places where you need continuous rotation without turning the wiring into the failure mode.

Q: Where do capsule designs have limitations that engineers should be aware of?

 A: The main limitation is that capsule is chosen to protect the mechanical envelope, so if your machine later “discovers” it needs a central bore, or a very large shaft passage, capsule stops being the right architecture.

 The other limitation is more subtle: in compact systems, teams sometimes keep adding circuits until they are mixing power and sensitive signals without a proper architecture behind it. When that happens, the slip ring becomes blamed for noise or intermittent behaviour that is really caused by the overall system layout and grounding and shielding approach. Servotecnica’s own engineering guidance consistently treats signal integrity as a system level design topic, not a checkbox.

Furthermore, capsule slip rings are not suitable for high current applications.

Q: How does that differ from a through bore slip ring?

A: A through bore slip ring is designed around a hollow centre. That single design feature changes how the slip ring integrates into the machine.

Instead of sitting beside the rotating shaft, it becomes part of the rotating structure itself. The bore allows engineers to route a shaft, pneumatic lines, cables, or other mechanical components directly through the centre while still transferring power and signals across rotation.

Servotecnica’s through bore solutions are widely used in robotics, packaging systems, rotary tables, wind turbines, pharmaceutical equipment and industrial automation. They are particularly useful in applications where mechanical integration must remain clean and where multiple services need to pass through the same axis.

In many cases, if a shaft is already present, through bore is the most natural architecture.

Through bore slip rings allow high current transmission.

Q: Flat or pancake style slip rings are often treated as “special”. When do they become the best option?

A: Flat exists for one very practical reason: height.

A pancake style architecture gives you a low profile axial length because the circuits are developed concentrically rather than stacked along the axis. Servotecnica’s own comparison explains this clearly: if your envelope is constrained in the vertical axis but you can accept a wider footprint, pancake style becomes attractive.

Where people get caught is assuming “flat” is simply “a thinner drum slip ring.” It isn’t. The geometry creates different trade offs, particularly around how contacts wear, how susceptible the design can be to shock and vibration depending on construction, and how much power you should realistically expect the flat format to carry in a stable way.

Q: With these different types available, what is the most common mistake you see in selection?

 A: The most common mistake is focusing only on shape. Engineers might say, “I need something small,” or “I need something flat,” without fully considering how the slip ring will behave in real operating conditions.

A slip ring is part of a complete system. It interacts not only with electric signals and power but also with vibration, temperature changes, duty cycles, and installation constraints. If those factors are defined clearly at the beginning, the choice between capsule, through bore, flat, or fibre optic usually becomes much clearer.

Q: How does Servotecnica support customers in making the right decision?

 A: We work closely with customers from the early design stages. Often, it’s not about selecting a catalogue part immediately. It’s about understanding the application, identifying potential risks, and sometimes adapting the solution so it integrates properly into the machine.

That collaborative approach is important because small design decisions can significantly affect long term reliability. Our goal is to ensure the slip ring becomes an enabling component rather than a maintenance concern.

Thanks to our decades of experience, we’re able to guide our customers and help them make the right choice.