Maintenance-free slip ring alternative for mission critical
military and aerospace applications worldwide.

Diamond Roll-Ring: Roll-Rings for Naval Radar

Air Search Radar

Diamond Roll-Ring: Roll-Rings for Mobile Artillery

Mobile Artillery

Diamond Roll-Ring: Roll-Rings for Patriot Missile System

Missile Defense

Diamond Roll-Ring: Roll-Rings for Air Traffic Control

Air Traffic Control

Diamond Roll-Ring: On Space Station Freedom

International Space Station

Diamond Roll-Ring: Benefits for Mission Critical Applications
Maintenance Free
Long Life
Milliamp to 2,400+ Amps
Very Low Torque
Shock Resistant
Low Signal Noise
Data Transfer Rates
0 - 3,000 rpm
High Transfer Efficiency
Custom designs


Roll-Rings are designed to roll. Slip-rings are designed to wear. The maintenance-free benefit of Roll-Rings is derived from its design concept, a ring of spring copper rolling between two conductive races. Slip-rings must create wear debris to function properly thus requiring periodic maintenance.

Diamond’s Air Traffic Control Roll-Ring units must operate without interruption to keep skies safe. To understand just how long a Roll-Ring would last in service, a standard unit was operated at 200 rpm for well over two years and accumulated 240 million revolutions or the equivalent of thirty years in Air Traffic Control search radar service. After the test was concluded the Roll-Ring was evaluated and found to perform in specification. Diamond Antenna & Microwave has supplied over nineteen countries including the US Military with multiple channel Air Traffic Control rotary joints with Roll-Rings since 2001. To date no Roll-Rings have been returned for service.

Long Life
Roll-Rings are made from a spring copper alloy then plated for low electrical resistance and corrosion resistance. Roll-Ring Engineers design the gap between the races such that the spring copper Roll-Ring will never accumulate fatigue stresses which would lead to a fatigue failure. The plating system chosen for the races and the rings is designed for long life with virtually no wear.

Roll-Ring units contain no wear items with the common exception of bearings and seals. The sixteen Roll-Ring units aboard the International Space Station have been in continuous service since activation with several of them operating in excess of ten years, all without any maintenance. A standard Air Traffic Control Roll-Ring® unit underwent accelerated life testing for 240 million revolutions or the equivalent of 30 years uninterrupted operation. In other words, each Roll-Ring rolled 63,480 miles or 2.5 times around the earth before the test was concluded.

Current Handling

Roll-Rings are designed to handle low noise signal circuits, 0-15 milliamps, to high current power circuits for wind turbines, over 200 amps per Roll-Ring. ¾” diameter is the smallest Roll-Ring currently designed into new units with the largest at 3” for wind turbine generator service.

Roll-Ring Engineers start with a customer’s current requirements then calculate the necessary number of races to safely handle the current at operating condition. There is no upper limit to the ability of a Roll-Ring system to handle current. As of May 2012 a 1,200 Amp 1,800 rpm unit is in operation in the R&D center. The next iteration will be capable of handling 2,400 Amps.

Roll-Rings do not require relative motion to be able to pass current and can remain in one position indefinitely without degradation in performance. While most Roll-Ring units are designed to handle full in-rush currents at 0 rpm, some, like wind turbine applications, can double their current carrying capability by passing full current only under rotation.

Very Low Torque

The original design intent for Roll-Rings was to drastically reduce the torque required for slip-rings used in directional and attitudinal gyroscopes for aircraft. The first Roll-Ring device ever produced reduced slip-ring torque in gyroscopes by 99%.

Roll-Rings do not require friction to enable contact like slip-rings. The Roll-Ring rolling interface is much like a steel railroad wheel on a railroad track, if given a push and a flat section of good track it will seemingly roll forever. The torque of the 2,400 amp Wind Collector Roll-Ring unit comes only from the two bearings that maintain the spacing of the rotor and stator relative to each other. By netting out the effect the bearings, there is no practical measurable torque required to rotate the Roll-Rings inside a 2,400 amp unit.

Shock Resistant

Roll-Rings are made from spring copper and are under slight compression when installed in their races. Combining well designed rotor and stators frames with a good bearing system keeps the races in close relative position to one another during extreme shock and vibrations. This close relative race position combined with the properties of the spring copper means the Roll-Ring is well captured and because of its very light weight is not strongly affected by high shock or vibration loads.

Slip-rings utilize a spring of one form or another to hold the brush contact against the rotor. Since the spring is constrained only by its spring constant a shock or vibratory load can cause the brush contact to momentarily leave the surface and potentially draw a damaging arc. Roll-Rings do not have this issue by design.

Low Signal Noise

Units with two Roll-Rings per channel, the standard configuration, routinely demonstrate noise in the +20 mΩ range. If an additional Roll-Ring is added in parallel with the first two, noise can be reduced to the +10 mΩ range. Speed does have an impact on the noise measured and each application must be reviewed individually by Roll-Ring Engineers to provide the best estimate of performance.

Data Transfer Rates

Roll-Rings have been proven to successfully transfer data at 15 Mbit/sec for RS-485 signals while rotating at 1,200 rpm. Roll-Rings are also capable of transferring a variety of other signal types including RS-422 and RS-232.

The diameter of the clear bore drives the data rate capability. As the diameter increases additional mitigating design techniques must be employed to maintain performance. Roll-Ring Engineers are continually testing the upper data transfer capability of various design configurations as they are manufactured. Power Over Ethernet (PoE) is slated for Roll-Ring testing during the summer of 2012.

Rotational Speed

Air Traffic Control Radar Roll-Ring units are capable of operating at above 3,000 rpm. The ability of a Roll-Ring device to operate at high speeds is a function of the clear bore allowed in the customer’s application. The smaller the clear bore the faster the Roll-Ring unit can spin and maintain performance.

Roll-Ring Engineers are continually evaluating their products to determine the upper operating limit of the design. Pictured below is one test fixture rotating an ATC Roll-Ring unit at 2,400 rpm for an accelerated life test.

A customer requested Roll-Ring Engineers design a 6,000 rpm unit capable of conducting 1,000 amps for greater than one year of continuous operation minimum. Slip-ring companies declined to bid on the application due to the speeds. An initial design was completed to successfully handle the speed required.

High Transfer Efficiency

Roll-Rings roll in races that are gold plated. Roll-Rings themselves are gold plated. This gold on gold interface provides for very low electrical resistance as well as a surface completely resistant to oxidation. 3” Roll-Rings for wind turbine generator service measured at 2.65 mΩ in rotation which equates to a transfer efficiency of 99.735%. This calculates to a power loss in a wind turbine generator application of 954 Watts total. Comparable numbers for slip-rings are not published by their manufacturers.

Custom Designs

All Roll-Ring products are designed, manufactured and tested in Littleton, Massachusetts. The New England area of the United States contains a vast array of suppliers which enables Diamond Roll-Ring to source components locally with rapid turnaround for prototypes or large production runs at competitive economics.

This excellent supply base combined with a talented local labor force enables Diamond Roll-Ring to design and build custom Roll-Ring units in as little as five and one half week s after receipt of order. Normal lead time is 12-22 weeks depending on complexity or required design iterations. We welcome the opportunity to work with you to design and supply your Mission Critical Diamond Roll-Ring device.

Diamond-Roltran, LLC        978-486-0039       59 Porter Road, Littleton, MA 01460