SRS up to the job for complex server rack design

Edited by the Engineeringtalk editorial team Jun 8, 2000

SRS was selected as the company that would work together with CCC and its designers to form a three-way partnership to develop the mechanical aspects of the Freevision subrack and front panels.

Companies developing systems at the forefront of technology often have their resources geared to elements related to the ultimate product vision.

CCC started to develop the Freevision Server Management System some two to three years ago.

Its engineers recognised that to achieve the mechanical design aspects of the system in the given timescales, this element ought to be left to the experts, who have the experience and 'know how' to steer the design around all the possible pitfalls.

Time was of the essence and CCC's engineers could not afford to engage in singular discussions with possible suppliers.

As a result, one meeting was convened where SRS Products' designers were invited to attend along with some of their competitors.

At this meeting, CCC designers presented their vision and what they wished to achieve in a particular timescale, then each potential supplier was asked to present its proposed solution.

Resulting from this, SRS was selected as the company that would work together with CCC and its designers to form a three-way partnership to develop the mechanical aspects of the Freevision subrack and front panels.

Constraints were numerous and, due to the value and prestige of the final product, external styling/appearance was of paramount importance.

Next to this came the mechanical, performance and environmental aspects, all of which had the potential to hinder the visual aspects.

The design concept had to incorporate modularity to allow expansion and customer specific configuration.

CCC had already committed to a backplane design that combined DIN41612 connectors plus 2 mm pitch High-Density Metric connectors.

This combination enabled the number of pin-outs and power performance to be achieved.

Whist this combination satisfied the inter-connectivity requirements, it imposed a major mechanical problem - that of how to plug and dis-engage the daughter cards into the backplane where the pin density represented an insertion/withdrawal force greater than a normal push/pull action could achieve.

In addition, it was also identified that transmitting this force through the daughter card created stresses, which had a detrimental effect on the tracking and components.

SRS considered and modelled a number of solutions, including a screw jack concept where the force came off the leading edge of the card.

The final solution used inject/eject levers, which could operate from a specially contoured rail profile.

To prevent distortion within the PCB, bracing/stiffeners were designed to pick up on key stress points, bypassing components and tracking to eliminate any potential damage.

The final product, being aimed at global market, needed to meet the European Directive for EMC emissions and immunity for this class of product.

To achieve the level required could have been quite simple if it was not for the need to dissipate a high level of heat.

Temperature demand is high and CCC uses a forced-air solution, maintaining a high level of EMC performance.

Various perforation patterns were tried which ranged upto 65% free air, to find that a greater percentage was required.

To meet both constraints a Honeycomb vent was fitted to the top and bottom of the subrack providing 95% free air and with the honeycomb acting as a wave guide it provided an extremely efficient EMC shield.

As the project progressed SRS maintained a close link with CCC so that when it reached the pre-production stage, the design was within spec, in terms of performance and appearance, but needing a review to bring down the cost.

Working in partnership with CCC, SRS put forward ways of changing the design such that it did not compromise its qualities but reduced cost through either taking cost from components within the assembly, negotiating better pricing with suppliers and making the final unit easier to build, reducing cost at the final system build stage.

This process has been followed all the way into production where both SRS and CCC make a contribution to implementing ideas for improvement on a continuous basis.