Capsule slip rings: series compared and how to specify

What a capsule slip ring is

A capsule slip ring is a compact, solid-centre rotary electrical joint that passes power and signals from a fixed frame to a rotating assembly. Precious-metal brushes, usually gold on gold, ride on a stack of small-diameter rings inside a sealed cylindrical housing, so surface speed, contact noise and wear all stay low. Because there is no bore, the unit sits on the axis of rotation, typically fixed by a flange at one end with flying leads leaving each side. Capsules carry many signal circuits and modest power in a very small envelope.

When to choose a capsule slip ring

Choose a capsule when the centre of the rotating axis is free and space is tight, as in camera heads, small turntables, sensor heads and robot wrists. Small rings give low drag torque, low electrical noise and long life, which suits analogue, encoder and low-level data signals. The trade-offs are current and access: power rings are typically limited to a few amps each, and nothing can pass through the middle. If a shaft, hose or cable must run along the axis, a through-bore design is the better fit.

How to specify capsule slip rings

Number of circuits, split into power, signal and data
Current per circuit (A) and working voltage (V AC or DC)
Maximum and continuous speed (rpm)
Envelope: outer diameter and length (mm)
Signal types: analogue, encoder, RS485, CAN, Ethernet or video
Ingress protection (IP code) and temperature range (°C)
Lead length, wire gauge and connector terminations

Common mistakes

Pushing one ring past its current rating instead of paralleling two or more rings per conductor
Mixing motor power and low-level signals on adjacent rings without screening or allocation planning
Fixing the rotor rigidly to a shaft that runs out, so bearing loads go through the capsule
Letting the leads act as the anti-rotation device instead of fitting a proper torque strap or pin

Series compared

Brand	Series	Circuits	Current	Speed	Bore / OD
Motion Control Products	AR/BR/CR Series Capsule Slip Rings	76	15 A	300 rpm	OD up to 35.5 mm
Moog	SRA-73540	12	2 A	250 rpm	OD up to 11.17 mm
Moog	SRA-73625	18	2 A	100 rpm	OD up to 11.18 mm
Moog	AC6373	12	2 A	100 rpm	OD up to 12.7 mm
Moog	SRA-73762	24	2 A	250 rpm	OD up to 15.5 mm
Moog	SRA-73526 / SRA-73528 / SRA-73599	24	2 A	250 rpm	OD up to 22.1 mm
Moog	AC6023	24	2 A	250 rpm	OD up to 22.1 mm
Moog	AC6305	15	5 A	250 rpm	OD up to 22.1 mm
Moog	AC6310	9	10 A	250 rpm	OD up to 22.1 mm
Moog	SRA-73574 / SRA-73587	36	10 A	250 rpm	OD up to 22 mm
Moog	AC6355	56	5 A	250 rpm	OD up to 25.4 mm
Moog	AC7356	56	10 A	250 rpm	—
Moog	AC7094	48	5 A	250 rpm	OD up to 55.1 mm
Moog	AC7036	—	15 A	150 rpm	OD up to 78.74 mm
Moog	AC7212	—	10 A	250 rpm	OD up to 99.06 mm
Moog	P Series	8	14 A	600 rpm	OD up to 31.7 mm
Moog	Rotoflux ESR 70	24	20 A	200 rpm	OD up to 70 mm
Moog	Rotoflux ESR 110	32	30 A	150 rpm	OD up to 110 mm
Moog	Miniature gold capsules (AC264, AC267, AC6292, RE4815, RK4288)	95	2 A	600 rpm	—
Moog	M Series (1021202)	120	2 A	1000 rpm	OD up to 68.6 mm
Servotecnica	SVTS A (A 01-A 07)	56	8 A	500 rpm	OD up to 25 mm
MOFLON	MC Series capsule slip rings	56	2 A	—	OD up to 25 mm
Senring	M Series capsule slip rings	56	30 A	—	OD up to 30 mm
Princetel	SR223 series	40	—	100 rpm	—
Rotary Systems	Capsule slip rings (SR009, SR010)	—	3 A	750 rpm	—
Meridian Laboratory	ROTOCON M series (end-of-shaft)	100	35 A	—	—

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 capsule slip rings are used

Robotics & robot wrists Packaging machines & rotary indexing tables CCTV & pan-tilt cameras Gimbals & drones Rotating test rigs & dynamometers Bottling & filling machines Stretch-wrapping & flow-wrapping machines Mixers & process vessels Satellite communication antennas (SATCOM on the move)

Capsule slip rings: frequently asked questions

What is the difference between a capsule and a through-bore slip ring?

A capsule slip ring has no central hole and mounts on the end of the rotating axis, which keeps the rings small, drag torque low and life long. A through-bore slip ring has a hollow centre so a shaft, air line or cable can pass along the axis. At equal rpm, through-bore rings run at a higher surface speed and are larger, so choose by whether the axis is free.

How much current can a capsule slip ring carry?

Signal rings in a capsule typically carry well under an amp, while dedicated power rings are commonly rated at a few amps up to around 10 A depending on the design. For a heavier load, several rings are paralleled on one conductor, which uses up circuit count and length. If the machine needs tens of amps, a through-bore or purpose-built high-current unit is usually more practical.

Capsule slip rings