Pancake slip rings

What a pancake slip ring is

A pancake slip ring, sometimes called a platter or flat slip ring, arranges its rings as concentric circles on a flat disc rather than as a stack along a shaft. Brushes press axially onto the face of the disc. This makes the assembly very short along the axis, often only a few tens of millimetres, at the cost of a larger diameter as circuits are added. Most pancake designs also have a central bore, so a shaft or services can pass through the middle.

When to choose a pancake slip ring

Choose a pancake design when axial height is the tightest constraint, such as in low-profile turntables, medical tables, rotary platforms under a payload or equipment mounted against a bulkhead. The trade-offs are circuit count and speed: each extra ring adds diameter, outer rings run at higher surface speed and the flat face is more exposed to debris. For many circuits in a modest diameter, a barrel-type through-bore unit is usually more economical. Speed ratings are typically lower than for capsules.

How to specify pancake slip rings

• Maximum axial height and outer diameter (mm)
• Bore diameter (mm)
• Number of circuits and current per circuit (A)
• Voltage between adjacent rings (V)
• Speed (rpm)
• Contamination exposure and sealing (IP code)
• Orientation: horizontal or vertical axis

Common mistakes

• Asking for many circuits in a pancake format, which drives diameter and cost up quickly
• Ignoring axial runout of the mounting face, which changes brush pressure around the turn
• Leaving the ring face exposed to dust or swarf without a cover
• Specifying high speed without checking the surface speed of the outermost ring

Series compared

Maximum figures across each series, summarised from manufacturers' published data on the date shown on each series page. Always confirm against the current datasheet.

Where pancake slip rings are used

Pancake slip rings: frequently asked questions

When is a pancake slip ring better than a barrel slip ring?

A pancake slip ring wins when there is very little axial space but room to spread out radially, such as under a flat turntable. A barrel or through-bore design wins when you need many circuits, higher speed or a smaller diameter. If both length and diameter are tight, the circuit count usually has to be reduced or some signals multiplexed onto a data channel.

Do pancake slip rings have a lower speed rating?

Often, yes. Because the rings sit at different radii, the outermost ring runs at the highest surface speed, and the flat face makes brush dynamics more sensitive to axial runout. Pancake designs are typically used at modest speeds. If the application turns quickly, check the rated rpm against the largest ring and consider a barrel design instead.