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Centistokes for Different Strokes

A collegiate contest pits fluid power against the venerable bike chain

Paul Sharke -- Design News, February 27, 2006

Hydraulics are messy, noisy, uncontrollable, wasteful and bulky. Bicycles are clean, quiet, manageable, efficient and light. For the first time, last year, hydraulics giant Parker Hannifin set about uniting these disparate traits with its Chainless Challenge, a student engineering contest in which teams built and raced bikes that didn't connect wheels and riders through any direct chain.

Several teams in the contest took the idea even further by dispensing with chains and sprockets altogether. Others employed chains in final and intermediate drives or to power a pump from the pedals. All were okay, as the rules only stipulated that any chain between pedals and wheels disappear.

The idea wasn't about building better bikes, according to Parker Vice President of Technology and Innovation Joe Kovach, who sat down with Design News some time after the race to critique the entries. The contest was about unleashing student interest on hydraulics. The hope is that one day some of these students will tackle that list of troubling traits. Future energy efficiency depends on hydraulics that are clean, quiet, controllable, miserly and small. This contest rolls us, ever so slightly, toward that end.

After a year of work, teams from nine universities gathered last August at a Cleveland park to test their designs. Teams raced in sprint and endurance contests.

The course:

Endurance racers rode three laps around a 4-mile loop, including a 300-ft, 1-mile climb away from the starting line — a 12 percent grade in spots. Teams used two riders each to complete the course. Starts were staggered on two-minute intervals. Safety marshals accompanied each team around the course. Sprint riders raced against the clock along a 100-ft, level track.

The bikes: Win, place, and show

1 Winner overall —University of Illinois

This entry used a chain-driven gear pump to supply glycerin to a hydraulic gerotor motor near the rear axle, which turned a chain and sprocket attached to a 7-speed hub. This entry also took top honors for manufacturability, marketability and cost, in addition to winning the circuit race. University of Illinois actually submitted two entries, an upright and a recumbent, that used identical drive trains. The teams behind the entries collaborated early and devoted a ton of time to research, including dynamometer testing of four prototypes.

This bike's drive train was remarkably similar to the entry from U of Akron, Kovach says, but it won for two main reasons. Using viscous glycerin instead of hydraulic fluid helped the U of I team bump up volumetric efficiency of low pump input speeds, something the Akron team accomplished by driving through an elegant planetary reducer made for bikes. As slick as this hardware solution was, Akron gave up some 2 percent efficiency simply by going through a gear mesh, he says.

The gear pump delivered 8 cc of glycerin per revolution to the motor, which produced 1 revolution for every 12 cc of fluid it received. The resulting 66 percent mechanical reduction was then reduced again through a chain and sprocket to the rear wheel and a seven-speed internal hub.

"An elegant design," Kovach says.

	The Murray State team made full use of stored energy to win the sprint.The bike also took honors for workmanship which shows.

2 Second place — Murray State University

The Murray State University trike used two accumulators charged to 2,500 psi to store energy for the drag race. Clinching the title was then a matter of charging the accumulators before the race and shifting a valve at the start to blast off toward the finish line in under 12 seconds. The relatively heavy 137-lb entry also won in the categories of workmanship, reliability and safety.

Drag racing was clearly what the team had in mind when it provided a three-way valve by which fluid could be directed from pedals to wheels, from pedals to accumulators or from accumulators to wheels.

	An accumulator added mild boost for the Cal Poly entry. Higher strength carbon fiber accumulators weren’t available.

3 Third place — California Polytechnic State University

California Polytechnic State University students took second place in the endurance contest. Their 14-speed entry used a cam and follower on the pedals to drive a double-acting cylinder (1.25-inch bore, 6-inch stroke) to produce a flow of 43 gpm at a 90 rpm pedaling input.

The bike included a 5l, reinforced accumulator supplied by a tire-driven pump that could be activated by the rider through a lever mounted on the top tube. The accumulator stored fluid at 100 psi.

A 5.3-lb orbital motor on the rear wheel works through a chain and sprocket increaser.

Cal Poly's arsenal also included a nationally-ranked racer at the pedals.

Kovach says, "This team struck a nice balance between good pedaling and side loading."

Other Finishers

	University of Akron students understood the need to raise pump speed for efficiency. Mechanical loss through a multitude of gear meshes extracted a toll. The pump end of the Univ. of Akron machine produces 1250 rpm with 100 turns a minute at the crank.

4Fourth place — University of AkronStudents made their own frame and used a special planetary gear on the chain ring to increase the speed at which they drove a gear pump (http://rbi.ims.ca/4915-561). At 12.5 times the 100-rpm pedaling input, the 1250-rpm speed of the gear pump began closing in on hydraulic volumetric efficiency, Kovach says.

By eschewing accumulators of any kind, the team avoided a significant weight penalty (about 20 lbs each) after realizing that accumulators "wouldn't pay," Kovach says.

Students used a 27-speed rear hub.

5Fifth place — Western Michigan UniversityOne of three trikes in the race, this design used a 1:6 bevel gear speed increaser to up the speed of the gear pump. The pump drove a gear motor that turned the back wheel through a 2:1 fixed gear reduction. Students used a single accumulator to help in the drag race. Even without any gear change, "its speed was okay," Kovach says, calling the design "clean and lightweight."

6Sixth place — University of California-IrvineThe only bike in the contest using air power alone, this entry took the "most ingenuity" award. Students built 14, one-gallon accumulators which they tested to 300 psi. Like the WMU entry, no chain was used at all.

From the pedals, a two piece crank maximized the stroke to two, 2-inch bore, double-acting air cylinders, which charged the accumulators. At the rear, a 2-1/2 inch bore air cylinder powered the wheel through a single crank arm. The students controlled the air through a bank of digitally-controlled valves, timed off a single hall effect sensor magnet mounted on a rear spoke.

"This was what we were hoping for in concept," says Kovach. "Air was probably not the answer. There was nothing awkward about riding this bike. It felt good."

Other Entries

Purdue University —This trike design was the only entry to be rowed instead of pedaled. Rowing can double the power output of pedaling. Unfortunately, the design's limited 18-inch stroke length was too short to take full advantage of rowing's power potential, Kovach says.

University of Cincinnati —Like the team from Akron, this group modified its bike frame quite a bit, including configuring the bottom bracket to hold a crank arm centered between the pedals. Achieving what Kovach calls "pure lines of force," the crank drove a hydraulic cylinder pump, supplying fluid to a cylinder at the rear of the bike. This cylinder drove a modified scotch yoke that cranked the rear wheel. The bike lacked multiple speeds, making the hilly terrain of the course insurmountable, yet the bike dispensed with a fluid reservoir as well.

Cleveland State University — This entry ran short of time and wasn't finished for the race, giving the students a real taste for deadlines. But where all the other teams had built their drive trains from existing components, this school fashioned its own pump and motor, integrating them into the frame and wheel. The students were solving, in a fundamental way, some of the limitations associated with commercial hydraulics at slow rpms. "Very ambitious," Kovach calls it, and a concept that could prove competitive if it's finished in time for 2006.

	Racers were permitted to blow through a stop sign on the closed course at the bottom of a hill. Making them stop would have built a better case for using accumulators for powering up the hill that followed, Kovach says. Most riders merely let kinetic energy help them with the climb.

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