Genie S-60 Gets the Lead Out
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May 19, 2004 - The industry seemed to hold its collective breath in 2002 when Genie Industries was purchased by Terex Corp., Greenwich , Conn. Locked in an arms race of sorts with JLG, Genie had been turning out new products every couple of months. But, based on previous Terex acquisitions, many expected Genie's business model to dramatically change. Now back on track, Genie is again building new models at its Redmond , Wash. , facility. An all-new S-60 boom lift and the jib-equipped S-65 are the first major product introductions since that merger.
Genie's first 60-foot straight boom lift was introduced in 1991 and was brought to market with great acceptance. It has enjoyed a successful 12-year-run as one of the largest selling boom lifts of all time. Its popularity, however, was weighed down by one key issue. At nearly 27,000 pounds GVW, the inability to legally trailer two units together was a problem. And as the market tightened and competition raged, each pound added to the price of ownership, a luxury that the market could not continue to afford.
Part One of a two-part series follows on the all-new design of the Genie S-60 straight boom lift. Watch the next issue of Lift and Access 360 for my full opinion and final verdict of this new generation machine.
To overcome the inherent weight handicap steel presents, Genie thought way outside of the box when re-designing the S-60. The lightest conventional 60-foot boom lift available is from Snorkel International, St. Joseph , Mo. Snorkel relies heavily on aluminum boom sections and an internal boom linkage system to minimize weight. For years, its weight advantage at 20,700 pounds has been untouched by any competitive all-steel boom lift. Other manufacturers have employed swinging or sliding counterweights to limit additional weight. Many design considerations were addressed in reducing the S-60's weight. But two initiatives were the key to achieving a 21,000-pound gross vehicle weight-a nearly 20% reduction over the former model.
Boom extension and retraction
First, Genie eliminated dual over/under telescoping hydraulic cylinders used for extending and retracting the boom. One of the original motivations for using an all-hydraulic boom was European Union safety inspection requirements. Current standards call for the annual inspection and mandatory replacement of the steel cables used in a boom lift's extension retraction system. Not having to replace these was a great feature but with one major drawback. The issue with the over/under telescoping cylinder arrangement is the extra weight associated with using an additional hydraulic cylinder. Added to that is the extra hydraulic lines and oil needed to extend the cylinder rods.
In light of these benefits, how can Genie abandon its design in favor of the inherently lighter and less expensive cylinder/cable combination? The answer is that with improvements to that basic system, the trade-off is worth it.
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All internal components that require an annual inspection are visible by removing covers on the boom. The cables, sheaves, and cylinder are housed in one sub-assembly. Once the proper bolts and fittings have been removed or disconnected, the sub-assembly is easily removed from the back of the main boom. According to Genie engineers, the entire job can be done in less than two hours. My review of the S-60's service and parts manuals seems to satisfy Genie's assertions. The design concept appears sound and the procedure is straight forward. This makes the job of replacing the cable every five years, as mandated for CE certification, a much less daunting and costly task.
Genie could have achieved a significant weight reduction by simply converting the boom to the more common cable/cylinder extend and retract system. But the company didn't stop there, and the result is much, much more.
Centering the pivot point
The second and most fascinating facet of the S-60's transformation is accomplished with, what Genie calls, "Virtual Pivot Boom." The balancing act required for rotating telescopic boom lifts is a complex one, and counterweight is the key to maintaining that balance. But, you can't just pile it on without making sacrifices. Additional weight is more costly and results in reduced performance. Gradeability, flotation, and fuel economy are each affected. Additional weight increases wear and tear on many major components. Plus it costs more to transport.
So how did Genie successfully shed so much counterweight? For starters, for every pound removed from the boom, it was possible to remove about three pounds from the swing counterweight and six pounds from the belly counterweight. At least that's a good approximation for this specific machine. When you multiply nine pounds for every one cut from the boom assembly, you quickly realize that the weight savings is huge. But, more central to the transformation is a design that shifts the machine's center of gravity.
The main boom is attached to four bar linkages. (See Image 2.) Internally at Genie these are called short and long links. The previous boom design required weight to be transferred from the boom side of the machine to the rear of the unit as the boom elevated. Now, the linkage transfers the boom's pivot point or fulcrum closer to the center of the machine as the boom is raised. As a result, the amount of weight loaded over the rear and the backward tipping moment are greatly reduced. Centering this weight as the boom rises translates into a much lower amount of counterweight required to keep the machine in balance. You can see how the end of the boom, once totally elevated, is positioned so that it points directly down at the center line of rotation. This differs from older Grove and Skyjack designs that employed moving counterweights. In the Genie design the counterweight never moves-only the boom does.
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The new geometry did, however, present a small engineering problem with the platform leveling system. A traditional master/slave hydraulic system is utilized, but with a twist. Note the long rod running vertically down the center of the machine in Image 3. This is what Genie calls a platform leveling link. It is connected to a master cylinder bell crank that is in turn linked to the master cylinder.
In light of the new S-60, Genie's impending announcement of a mega-articulating boom lift along with numerous product upgrades, it seems Genie has made a return to its ambitious business model. The S-60's all new design is part of the company's goal to build equipment that delivers maximum up-time while being easy to service. And, although the boom design stands out, it is not the only improvement you will find on the S-60. A more efficient design enabled much of the machine's cost to be rationalized through smaller and less expensive components, such as bearings, axles, motors, and fabricated structures. Next issue, I will discuss other design changes and how they have been adapted to qualities that existed previously on the Genie S-60.
