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October 6, 2003
6 Min Read
Nostalgic images of soap box derby cars recall parents and kids from the 1940's and 50's happily sawing plywood and borrowing wagon wheels. But when the 21st century racecar carries the Porsche nameplate, about the only remaining part of that image is the happiness part.
Engineers at the Porsche Design Studio in Huntington Beach, CA recently used advanced CAD tools and lightweight aerospace materials to build a sleek vehicle that blends the spirit of a California surfboard with the rules of the soapbox derby. The result was a racer called a soapboard, which beat every other vehicle it raced by at least one length.
Porsche designers and several of their counterparts at a number of supplier companies donated their time and materials to build a car raced in a charity event for America Works for Kids, a national group that works with foster children.
Many other companies, including other automakers, sponsor cars, but most of them are far more conventional than the Porsche design.
That design attracted a fair amount of media attention for the Gravity Car Derby. "We decided to have some fun building a super high tech soap box derby car," says Roland Heiler, director of the Porsche Design Studio.
Building the soapboard with today's conventional materials-plywood or fiberglass- was never a consideration. The Porsche body is created with a composite material consisting of carbon fiber layers interspersed with layers of honeycombed aluminum. It was made by a Porsche partner that normally uses the composite for NASA projects, aircraft, or other applications that require very low weight and high structural strength.
The body and chassis weigh only 17 lbs. The wheels add nearly the same amount of mass, making the total weight around 30 lbs. That is well below the 88-lb weight limit for the vehicle. "The beauty of a lightweight vehicle is that you can put the weight where it's needed for the best performance," Heiler says.
That spot is high on the rear of the bike. Lead is placed there so that when the soapboard is at the top of the wooden ramp at the start line, the stored energy is at the highest point. This gave the design a leg up, so to speak, since the work performed is a function of the vertical displacement of the center of gravity of the body.
The design process also underscored the way the world has changed since tape measures were used to build plywood racers. The soapboard racer was designed using the CAD tools used during the day to create Porsches. That includes Dassault Systemes' Catiasoftware and Alias Wavefront from Silicon Graphics Inc. "We went straight from 3D computer models to the tooling, with no clay models. The first time we saw this in 3D was when it came out of the mold," Heiler says. However, he notes that they did build a mockup using wood, bringing in some of the designers' children to test the ergonomics.
Though the design is so minimal it conjures up images of a racing bicycle,
engineers quickly found that they couldn't borrow all their components from the cycle racing field. The front wheels are at the end of the axle, so bike wheel hubs designed for support from both sides of a fork were out of the question.
But there are other wheel hubs that are used in competitive racing. "We got the style of hubs they use in the wheel chair Olympics," Heiler says.
The wheels got plenty of consideration, beginning with the decision to use only three. That minimizes rolling resistance. The team used ultra-light carbon wheels and high-pressure tires, further reducing inertia at the start of the race in addition to minimizing rolling resistance.
The vehicle is stopped with V brakes, a common racing bike technology that has good balance from right to left. The brake handle is handmade so it can be integrated into the handle-bar.
Fragile, thin, and delicate are among the terms used to describe the racer, but those traits aren't necessarily positives when a one-of-a-kind vehicle meets the real world. Porsche engineers created a design they figured would survive a number of runs, and durability was also considered by companies that donated materials and built the soapboard.
But determining whether they were over or under-designing for strength was tough, since the height of the ramp, its angle, and the size of the pilot were not known during the design phase. Knowledge that the 475-ft track was not curved helped little but did remove the need for a true steering mechanism.
Winning Wet Suit
On race day, team members held their breath as they watched the first run on a less-than-optimal surface. "I was shocked to see the street. On the first run, the front tires were bouncing 10 centimeters off the pavement," Heiler says.
The pilots were undoubtedly happy that the soapboard didn't fall apart like some derby cars on TV or movies. They went down the track head first, becoming part of the vehicle when most of their body squeezed into an integrated wet suit. "We wanted an aerodynamic design, but we had concerns, including what would happen if you had kids wearing floppy clothes. Then we came up with the wet suit idea," Heiler says.
To carry on the surf board theme, the stylists made a neoprene wet suit part of the vehicle's frame. Pilots slide into the suit, which can stretch to fit the array of body sizes for children aged 7 to 12. "We got better aerodynamics by introducing a small windscreen to direct air around the driver's helmet," Heiler says.
Porsche employees often worked late into the night to meet deadlines, as did many of their suppliers. But the big payoff came when the foster children got to pilot the soapboard. "For kids who don't have a lot of material things, to drive Porsche was great. You should have seen the smiles on their faces," Heiler says.
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