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At the Field Musuem of Natural History in Chicago, an exhibit called Nature Clouds features four hanging gardens, or ‘clouds’, showcases plants from the prehistoric era above the museum floor.

In total, 28 tons had to be lifted, with the four clouds weighing between 5,000–19,000lbs each.

The clouds, designed by Branch Technology, have 279 3D printed parts, and include more than 12,000lbs of vegetation and support equipment weight, 9,650lbs of steel and almost 4,000lbs of printed component weight. The clouds have a travel speed of 16 feet per minute with variable speed in acceleration and deceleration. They travel to three pre-set positions using a wireless pendant on the main floor.

The engineering solution to raise and lower the clouds was developed by Chicago Flyhouse. “We have done many projects of this scale and larger,” said David Millard, project manager. “We specialise in the unique and difficult. This fits the criteria of a unique and difficult project that required immense attention to detail and aesthetics.”

The hoists, which were custom designed and manufactured by Flyhouse, are wire rope hoists with custom double helix groove zero fleet drums. The hoists’ capacities range from 5,000–19,000lbs, with two large and one medium capacity hoists for the clouds. The hoists also have redundant braking and cable management systems.

“We did all the rigging during regular hours while no part of the museum was closed to visitors,” Millard said. “This required us to develop a custom suspended floor structure that was capable of supporting 28 tons over a 1,250 square foot surface that acted as a hoist and as a protective layer between our work and the general public 75 feet below us.”

Millard said the primary challenges involved designing hoists that could move the clouds quickly but which were also small enough to fit within limited spacing. They also faced multiple mechanical obstructions as they set up the rigging system in the small confines of the attic at the Field Museum. The Flyhouse team designed, engineered, fabricated, and installed three hoists between the museum’s lay lights and skylights.

To assist with the movement of the clouds, the Flyhouse team used a 75-foot energy chain from Igus, the Germany-based manufacturer of motion plastics. They designed a system through which a pulley allowed them to pull the chain at the bend of the chain, instead of the typical pushing or pulling at the end.

“We tied the movement of this pulley directly into the hoist,” Millard said. “We created a series of mechanical advantage systems to allow the pulley for the chain to travel at exactly one half the rate of the suspended clouds. Since we are moving the middle of the chain, the chain moves at twice the speed of the pulley at the bend in the chain, thereby making it sync exactly with the moving cloud.”

The energy chain is a standard product for Igus, but the centre support was an innovative application: “Supporting it at the centre with our custom pulley and controlling the movement from there instead of one of the ends is what makes it unique,” Millard said.

The energy chain also carries cables from Igus that provide water, power, and fibre-optic to the sculptures. Four of the Igus Chainflex cables, such as those for fibre-optics and air line for water, are 100 feet long. There is also a 300-foot cable, which is typically used in heavy duty indoor applications and in high bay warehouses, packaging machines and indoor cranes. The cables are designed to have a long service life and require little maintenance.

The energy chain needed to be wide enough to accommodate all of the various cables, which helped with the movement of the clouds.

“This particular chain was sized around the fill package which was provided to us by Chicago Flyhouse,” said Brad Stanley, the Igus representative who worked on the project. “If there would be additional needs to pull new cables, there is room to do so provided our rules of separation with any energy chain are met.”