Sun Microsystems created a new design concept for an improved rack-mounted computer server that uses space more efficiently, while maintaining low computing costs and high reliability. If Sun’s engineers succeeded, customers could free up space in cramped data centers without compromising IT maintenance or the server system’s uptime. After initial concept evaluation, Sun concluded it needed a partner who specialized in torque solutions to achieve its design objectives, so it engaged Reell Precision Manufacturing to design a highly specialized module support mechanism.

The Reell/Sun collaboration resulted in a compact, clutch-based vertical module mounting system that allows Sun to create enough additional space in a 19-inch rack for customers to store three servers in the same space that previously held two servers. Reell’s clutch-based module-support device makes the server modules reliably accessible from the top of Sun’s horizontal drawer slide rather than the traditional horizontal access. The reorientation improves reliability because it permits a straight airflow path and increases cooling. The Reell module support clutch eases reliable assembly and serviceability to the vertical module insertion.

The Design Challenges for Sun:

  • Increase the number of server systems that can fit into a 19-inch rack from two systems to three systems.
  • The more compact, rack-mounted system must meet extremely tight torque tolerances; airflow and cooling requirements, and stand up to the external vibrations of power-on service actions and the operation of adjacent equipment.
  • The system must meet Sun’s enterprise-class performance and reliability requirements for demanding installations in telecommunications and data centers.

The Design Challenges for Reell:

  • The server modules, which are heavy and fragile, must be accessed easily so they can be removed and inserted without damage. The customized clutch mechanism must allow an IT technician to let go of the server module at the top of the rack-mounted drawer and the clutch mechanism will support the module and allow the technician to safely lower it into place.
  • The new module support device must fit within a very limited space allowance.

The Solution:

Sun Microsystems called Reell to create a custom torque solution after other design concepts could not meet Sun’s requirements. Initially, Sun had contracted an outside design firm to help Sun’s mechanical engineering team design the rack-mounted system. Although the firm’s mounting system looked good in the first prototype, it did not survive Sun's rigorous test and review process.

“The original firm created a pretty elegant solution, but we couldn't guarantee it would work in all environments,” said Jay Osborn, Sun Microsystems Senior Engineer. “We needed a solution that could give us very high predictability of torque and accommodation of dimensional tolerances so we could keep tight control of the whole system.”

Sun evaluated 26 different mechanism concepts, including products from two other clutch providers. “Reell came out first and that’s why we selected them. Reell specializes in torque control,” Osborn said. “The other products did not have as tight of control on functional tolerances.”

Sun’s engineering team worked with George Larson, a principal engineer at Reell, to develop an effective solution. Sun and Reell discussed the functional specifications and engineering constraints and divided the design process between the Sun and Reell engineering teams according to who had the most experience in a particular aspect of the design. The team frequently compared the compatibility of Sun’s module mounting requirements and Reell’s clutch solutions.

Reell brainstormed cost-effective solutions based on the discussions and created a reference proposal, a risk assessment, and alternate designs. Sun’s engineering team adopted Reell’s design and sold the new rack-mounted server concept to management based on the projected increase in reliability.

Reell assembled a combination of a pinion gear, a one-way clutch, and existing Reell patented high-torque density friction components, to mate with a linear rack gear on the Sun modules which converted the clutch's rotary friction torque to the controlled vertical force required to support the module weight. This clutch assembly pivots with a spring bias on a mounting bracket to absorb chassis and module dimensional tolerances; the geometry of the clutch housing and bracket were designed so the gears would self-engage, eliminating "kick-out". Sun engineers designed the module-mounted rack gears to properly engage to and disengage from the pinion teeth at the beginning and end of the insertion stroke; the one-way bearing allows free lift of the module.

“The design process went extremely well,” said Osborn. “Reell didn’t just modify an existing product. They studied the problem and used common components to exactly hit the need. And they had fast prototyping that met all the final specifications.”

“Unlike many other suppliers, Reell supported the specific design we asked for but they also helped us understand the component behavior needed to optimize the design. They gave us a lot of performance curves, not just single numbers. They helped us understand how and why the mechanism would work under different conditions so we could make modifications and adjustments on our own,” Osborn said enthusiastically.

Looking back on the project, Osborn said, he found Reell to be extremely responsive. He also mentioned he appreciated Reell’s open and honest communication throughout the process:

“Reell always supplied good information and they clearly understood the product design issues. Other suppliers are protective about the inner workings of their companies. I was routinely impressed with Reell’s openness. We had some delicate design tradeoffs, and encountered a few technical issues we hadn't anticipated; when Reell had an issue to be resolved, they were very upfront – even for issues related to their own technology. We have a very small staff here and we can’t afford to spend a lot of time going back and forth with each supplier. It’s inefficient. Reell always anticipated our information needs so the entire process was efficient.”

Design verification and introduction of the clutch design into Sun's production line went smoothly, and the new Sun Fire V1280 server was brought to market in January 2003. Customer feedback on the module support system has been very positive, helping to ensure excellent market reception for the new server.