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For Decades, the Humble Pogo Stick was Built from the Same Basic Design. Recently, however, Three Entrepreneurs have Followed Different Paths to Create Sticks that can Launch People to Dizzying Heights.

[+] Author Notes

Michael Abrams is a freelance writer in New York City, and a frequent contributor to Mechanical Engineering.

Mechanical Engineering 134(08), 40-43 (Aug 01, 2012) (4 pages) doi:10.1115/1.2012-AUG-3

Abstract

This article discusses recent changes in the design of pogo stick. Entrepreneur Brian Spencer and his father, Bruce, have designed a new pogo, which they call a Vurtego. The father and the son began sketching out a bold new direction in pogoing in the late 1990s. On the suggestion of Bruce Spencer, they designed a tube using air compression rather than a spring. In the garage, Bruce Spencer cobbled together a first prototype from PVC tubing and other plastic parts, and this new pogo stick worked well. The air spring lifted Spencer well off the ground. Through a series of refinements and trials, Spencer discovered that the key factor was the compression ratio. In addition to patenting the design of their stick, the Spencers have now also patented a range of maximum compression ratios, between 2.5 to 1 and 4.5 to 1.

Article

Young people do stupid things for fun. Suburban garages are stuffed with the detritus of what were, in retrospect, dumb things that seemed like fun at the time. Paddle balls, Hula-Hoops, lawn darts—what were we thinking?

The pogo stick was once such a toy. You bounced up a few inches, you came down again, then repeated the cycle till boredom set in. A small subsection of pogo owners, however, found that bouncing for minutes, or even hours, on end, was a thrill. In the early 1980s, for instance, the world record (in the Guinness book thereof) for most consecutive hops was held, briefly, by one Jeff Kane, who pogoed 120,715 times in just over 16 hours.

The pleasure was simple enough that the pogo stick's design has survived the better part of a century with virtually no change. Why optimize when up and down is accomplished so efficiently? But recently, there has been a renaissance, a veritable punctuated equilibrium in stick design where engineers have looked for new ways to store and release the kinetic energy of a bouncing person.

And with those new designs, there has been a revolution in the way people use pogo sticks. Thanks to technology that stores and releases energy more efficiently than ever before, pogoing is now recognized as a sport, of sorts, as wild, dangerous, and breathtaking as anything you’d see at the X-games. At this year's Pogopalooza last month, you might have seen someone launch himself five, six, eight feet in the air. Or do back flips, or land with one foot, or bounce perpendicularly off a wall.

The new technology has turned pogoing from a joy of the stupid sort, to one a lot closer to crazy.

Extreme pogo, as it is called, got its first national exposure ten years ago at the Winter Olympics in Salt Lake City. Entrepreneur Brian Spencer trucked a few prototypes of a new, pneumatically powered pogo stick in from Orange County, California. Spencer convinced Olympic organizers to give him enough space for an extreme pogo demonstration.

The sight of Spencer and his compatriots rocketing around the demonstration grounds and into the air drew some gasps and all sorts of attention, including that of a television reporter. Would it be possible, the reporter asked, for Spencer to launch himself over the reporter during a segment on the pogo exhibition?

“I’m thinking there's probably a 50/50 risk of cracking him in the head,” Spencer recalled.

But the stunt went smoothly and Spencer—who had wanted the Salt Lake City event to promote his pogo stick—got his national exposure. Though it was great publicity, there was a downside: Spencer still only had prototypes. “We let the cat out of the bag on national television,” he said.

Spencer's pogo, which he called a Vurtego, was a radical rethinking of the basic pogo stick of childhood memory. That stick had changed little since Max Pohlig and Ernst Gottschall—the po and go of pogo—patented their federnd wirkende Hüpfstelze in 1920. An outer frame is kept from crashing into an inner piston by an internal coiled spring. Near the base of the outer frame are two footrests, much like that of a stilt. When the pogoer steps onto the footrests, his weight compresses the spring.

An air spring enables the Vurtego to launch pogoers to dizzying heights.

Grahic Jump LocationAn air spring enables the Vurtego to launch pogoers to dizzying heights.

That in itself won’t do much. But pressing down hard or jumping onto the footrests stores more energy in the spring than is needed to support the pogoer's weight; when that energy is released, the extra energy accelerates the rider just a bit into the air. Repeat that action again and again and again, and the pogoer can achieve the promise of Pohlig and Gottschall's spring-action hopping stilt.

Although venerable, the coil spring-loaded pogo stick has its limitations. You want the spring to have some give, but not too much or you’ll bottom out and waste the energy of the bounce with a bone-rattling jolt. Similarly, a stiff spring can be heavy, and if it's too stiff it becomes difficult to deflect it enough to get any height.

But there are other materials that can replicate the compression and expansion of a coiled spring, and Spencer was using one of them: compressed air. Spencer and his father, Bruce, began sketching out a bold new direction in pogoing in the late 1990s, after a random discussion at a family gathering. On the suggestion of Bruce Spencer, an aerospace engineer, the father and son designed a tube using air compression rather than a spring. In the garage, papa Spencer cobbled together a first prototype from PVC tubing and other plastic parts.

And it worked. The air spring lifted Spencer well off the ground. Unfortunately, he also kept bottoming out. Through a series of refinements and trials, Spencer discovered that the key factor was the compression ratio. In fact, in addition to patenting the design of their stick, the Spencers also patented a range of maximum compression ratios, between 2.5 to 1 and 4.5 to 1.

While Brian Spencer could put on amazing demonstrations with prototypes, at first he couldn’t get an investor interested in producing his pogo stick for the masses. In the meantime, SBI—the oldest and largest maker of pogo sticks worldwide— was heading to market with a design of its own. The stick was as much a departure from the traditional pogo as Spencer's Vurtego, and yet it was a distinct design of its own.

SBI Enterprises traces its heritage back to George Hansburg, who is credited with popularizing pogo sticks in America. And the company has been making the traditional spring-in-cylinder pogo sticks for decades. It was a steady if not spectacular business.

One day in 2000, however, an MIT-trained physicist named Bruce Middleton approached the company with a different idea: instead of coiled springs, why not use thick rubber bands to store and release the energy from each bounce? Such bands are capable of stretching as much as 400 percent and then snapping back to their original size, and the amount of recoil can be tuned by adding or removing bands.

“It was a tremendously unique concept,” said Irwin Arginsky, owner and president of SBI, “which we proved to be correct at enormous cost. It was easier to conceptualize than to implement it.”

Unlike spring-based sticks (or pneumatic ones such as the Vurtego) which involve compression, Middleton's concept required pulling on elastic loops. Those loops were eventually replaced by cords, much like thick bungees, that hung from the top of the internal piston and attached to the footrests. Step on, and the cords stretch to accommodate your weight.

The system of cords allows for some customization. Pogoers can engage or disengage the 12 cords as needed, enabling either a smoother ride—or a more propulsive one.

But the design, though innovative, was indeed not easy to implement. Anchoring the cords without causing them to tear, split, or snap under stress was a challenge. The cords themselves had to be specialty molded.

Another hurdle was an interminable patent process. Though Middleton “is probably the brightest, smartest, most intelligent person I’ve even met,” Arginsky said, “he has zero social skills. But the patent attorneys had to deal directly with Bruce, because he's the inventor.

“It was one of the most expensive things.”

Large R&D costs and the comparatively massive size of the new stick set the price point over $200—far higher than the conventional, coil spring-loaded pogo sticks SBI made. Though the burgeoning extreme pogoing community went gaga over the stick, dubbed the Flybar 1200, it was hard for SBI to sell enough of them to recoup the investment. “If I were to delve into it carefully, I’d say we break even,” Arginsky said. “But it gets us, literally, I don’t know how many dollars’ worth of publicity.”

Publicity can bring competition. The stunts of extreme pogoers launching to new heights on their Flybars or prototype Vurtegos got the attention of at least one inventor. Ben Brown, a project scientist at Carnegie Mellon's Robotics Institute, had been tinkering with hopping sticks for more than a decade before he saw his first extreme pogo demonstration.

“We got a foot off the ground and thought that was pretty good,” Brown said. “We thought we had the greatest thing in the world and then we saw the Vurtego guys. Brian Spencer broke the record at six feet. I found it hard to believe.”

Brown had been working to make robotic legs more efficient. The hydraulic pistons that supported the legs were great consumers of energy. A bow spring, on the other hand, could store and return 90 percent of energy with each step, and it could be scaled so that it “worked well for itty bitty robots,” Brown said.

The obvious next step was to scale up to human size. After trying a steel wire, Brown settled on fiberglass, with its high specific energy. Then, seeing extreme pogoers in action spurred Brown to develop something that could be more than a means for engineers to blow off steam in the lab. By 2009, he was ready to hand out a few of his prototype Bowgos at Pogopalooza, the annual gathering of pogo enthusiasts.

Other extreme sticks made headlines—Dan Mahoney set a new record, 8 feet 6 inches, with his Vurtego—but the Bowgo was wowing the cognoscenti. The stick looks different in action from traditional pogos: the bow, mounted in front, flexes outward during every landing. But while other kinds of sticks required effort to build up enough force to bound six feet in the air, the extreme efficiency of the bow spring enabled people to quickly launch themselves to height. Within a year of its public introduction, Mahoney's mark had been bested by Curt Markwardt on a Bowgo.

The Bowgo's flexing fiberglass strap stores and releases energy from each bounce.

Bearings helped increase the pogo stick's efficiency.

Grahic Jump LocationThe Bowgo's flexing fiberglass strap stores and releases energy from each bounce.Bearings helped increase the pogo stick's efficiency.

The bow spring wasn’t Brown's only innovation. Instead of the bushings that keep the inner piston aligned in other pogo sticks, Brown used roller bearings. According to Fred Grzybowski, the twenty-something considered to be the world's foremost pogoer, “Bearings reduce the friction when jumping. It's super smooth, smoother than a Flybar. It's also a death trap—slightly.”

The altitude that even a novice can attain on a Bowgo—height that he might not be ready to handle—is just one of the safety problems. The bows are not indestructible; one fiberglass bow broke and lodged itself in Markwardt's knee. After that, Brown stopped offering his sticks to interested parties.

Brown eventually licensed the design to Razor, the company famous for cornering the children's scooter market. Their BoGo stick features both an internal steel coil assisted by an external fiberglass bow spring. Right now you can head to any Toys-R-Us and buy one for your seven-year-old. He’ll be able to launch himself a foot or so off the ground.

The Flybar remains on sale, but its reputation has been plagued by the rapid disintegration of its all-important elastic cords.

In spite of its garage-built heritage, the initial difficulty in finding a fabricator, and a price that's far, far above the typical teenage allowance, Vurtego appears to have become the stick of choice for extreme pogoers. The company's latest products, made from aluminum in order to withstand greater maximum air pressures, allow for greater altitude. The most recent height record for a pogo stick bounce was set on a Vurtego: nine and a half feet.

Engineers can design better machines, but it takes young men to make them do crazy things for fun.

Copyright © 2012 by ASME
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