Unchained innovation

Oct. 6, 2005
Nine university teams recently tested their engineering skills and racing prowess on fluid-powered bikes.

The pneumato-bike from Univ. of California, Irvine, stored pressurized air in a series of accumulators and powered the rear wheel with a pneumatic cylinder.

Murray State's three-wheel recumbent bike featured an accumulator that stored energy for uphill climbs.

The Purdue row-bike team used a hydraulic cylinder as a linear pump, an improvement in efficiency over rotary hydraulic pumps, and estimated that rowing motion generated about 200 W of power compared with 90 W from pedaling a bike. Excessive weight hampered the design.

The essence of the Chainless Challenge, a design competition sponsored by Cleveland-based Parker Hannifin (parker.com), was to substitute hydraulics or pneumatics for a bicycle's direct chain drive and prove the concept in a 12-mile race.

Designs included two-wheel racers and two and three-wheel recumbent models. Hydraulic motors powered some bikes, others relied on hydraulic or pneumatic cylinders for motive force.

"Low-speed efficiency has always been an issue with hydraulics, and the idea of a hydraulically powered bicycle is a great way to illustrate some of the challenges this presents," says Craig Maxwell, Parker's vice president of Technology and Innovation. Students were given a year to design, build, and test a human-hydraulic powered bicycle. To rate the final products, teams squared off for three laps on a hilly, 4-mile road course, as well as a short sprint competition. Bikes were also judged on safety, manufacturability, innovation, marketability, cost, and other factors.

The Univ. of Illinois earned the top prize with a time of 1 hr and 21 min and a simple, lightweight design. Each of the five students on the team received a $2,000 scholarship.

They determined a gear pump offered the best trade-off between performance and cost, but driving it efficiently meant the pump had to run faster than the 90 rpm generated by typical bike riders. They overcame this problem by gearing up the pump and gearing down the motor with chains and sprockets. The motor attaches to a seven-speed gear hub on the rear wheel, which lets the rider adjust the final drive ratio up and down.

One idea the Illinois team considered but abandoned was storing energy in an accumulator. It would charge when riding downhill and assist in pedaling uphill. Unfortunately, simulations showed that charged accumulators would be beneficial in a sprint race, but would add 15 lb to the bike and ultimately increase lap time on the road course.

The team from Murray State Univ., Murray, Ky., learned that the hard way. Their three-wheel recumbent bike weighed 137 lb, with a pump, motor, accumulator, and other hydraulic components making up about 61 lb of the total. It offered several distinct operating modes. In one, pedaling pumped fluid to the motor and powered the bike, with any excess stored in the accumulator. A second mode simply charged the accumulator. And a third let the accumulator supplement power to the drive wheel. However, the accumulator's relatively quick discharge and added weight proved to be of little help on long inclines.

Among other interesting designs, the pneumato-bike from Univ. of California, Irvine, relied on air rather than hydraulics. According to the team, benefits included an environmentally friendly design as well as lower weight, cost, and pipe-flow losses. The downside was lower operating pressure and, thus, less stored energy than a hydraulic system of similar size.

The pneumato-bike's output was independent of input. The pedal crank cycled a cylinder that pressurized a series of plastic accumulators attached to the bike. Pressurized air, in turn, powered the rear drive cylinder. Microprocessors and position sensors determined when to fire valves that actuated the cylinder.

Other teams in the competition represented the universities of Akron, California Polytechnic (San Luis Obispo), Cincinnati, Cleveland State, Purdue, and Western Michigan.

The overall goal of the Chainless Challenge "was really not about the bicycle," explains Lawrence Schrader Jr., Parker's Global Motion and Control training manager. "We wanted to give students an engineering challenge to spur creativity and innovative thinking." "What they did was to take off-the-shelf components and arrange them in innovative ways to get the most out of what's available," says Maxwell. "That's a good starting point. But once you get your mind around the challenge, that's when really exciting things start to happen. That's the way innovation takes place, and that's exactly what happened here."

"Some of the approaches worked and some didn't, and that's not bad," adds Schrader. "This isn't a one-time deal. All the schools made their first design, gathered information, made mistakes, and looked at the competition to see what worked and what didn't. Now they have an opportunity to go back and improve the designs. Next year's times will be much faster."

The company is considering expanding the program to other universities and, perhaps, to the private sector as well.

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