Oxford, CT--The four-man bobsled careens 90 mph down the 1,700-meter long spiral track located in the foothills of Mt. Iizuna, Japan. The track drops 113 meters from start to finish. The driver deftly pulls the ropes left, then right to steer through the 15 sharp curves. As the sled speeds across the finish line, the brakeman expertly pulls the lever, praying that their time was within that 1/100 of a second needed to take the lead.
For the first time in almost 50 years, the U.S. bobsled team is in contention for an Olympic medal, thanks to the Bo-Dyn sled, a new design by Bob Cuneo, president of Chassis Dynamics. With an infusion of $200,000 of personal funds, NASCAR racer Geoff Bodine sparked the project that led to the U.S.-built machine, now racing in Nagano, Japan. "Prior to this, we were using old European sleds that we had to weld back together," says Tim Conrad, principal engineer of the U.S. Olympic Sport Science Technology Division in Colorado Springs.
The Bo-Dyn, originally introduced at the Lillihammer Olympics in 1994, has undergone major revisions in the last four years. "There were many factors we didn't understand then that we do now," says Cuneo. "We realized we hadn't taken into account the ergonomics of the athletes' bodies. So we redesigned the frame and cowling (the body) because the way the athlete rides in the sled has a large effect on the performance of the sled both aerodynamically and mechanically." To develop a more aerodynamic design, Cuneo viewed both the athletes and sled as a single unit. "These weren't two separate items--they were one and the same," he says.
The key engineering issue was control. "There are two elements of control--actual control and perceived control," says Cuneo. It is actual control when the car or sled does what the driver wants it to do at a specific speed. It is perceived control when the driver feels that he has dominion over the machine and, as a result, will take more chances. Cuneo sees a definite gain in racing performance when perception is increased.
A bobsled's speed is affected by three factors: the start (push), weight, and ice friction. To increase confidence in the sled, the athlete has to "feel" the track. In other words, there must be communication between the ice's surface and driver's body, "and it has to be friendly," says Cuneo.
Much of this communication is transferred through the sled's runners. "Runner technology really is a black art," says Cuneo. "Many athletes will have 20 or 30 sets of runners per sled depending on conditions." Ice surface, sun or clouds, humidity, and temperature--even changes of a degree or two--will affect the speed of a race. Each set of runners is designed with a slightly different curvature, cross sectional radius, or chemical composition that corresponds to the situation. Al-though no one yet exactly understands why a particular shape or metal works differently under varying conditions, Chassis Dynamics is "trying to turn the black art into science," says Cuneo.
Another aspect of the ice-to-driver relationship is sled stiffness. Because of the tight constraints set by the International Bobsled Federation, there are few components one can alter to improve the design, says Conrad. Olympic rules confine the construction of sled bodies to carbon fiber, Kevlar, or fiberglass. Only steel can be used for the chassis and runners. By altering the thickness and composite of the various materials on the cowling, stiffness of the machine can be refined.
The thickness of the frame, shell, and runners all contribute to the rigidity of the sled, says Conrad. Because one can't build the frame stiff enough, body hardness has to be added, while maintaining flex in the machine. If the body is too stiff, the bobsled bounces all over the track. If too soft, it is uncontrollable.
Chassis Dynamics worked with Ken Armstrong of Creative Instrumentation (Davidson, NC) to develop an elaborate testing package that helped determine the optimum design. The system monitors articulation, front axle swivel angle, rotation of runner shoes on axle, the lateral G's on the machine, speed, acceleration, as well as vibration on all parts of the sled. Any motion-control technology was fair game--computer simulations, gyros, accelerometers, and IR lasers, were all included in the test program. The sled was originally designed using CADKEY, a CAD software package from Baystate Technologies (Marlboro, MA).
"Last year we were the hottest team on the circuit," says Cuneo. "We've won more metals in the last five years with the new design than we've won in the past 50 years combined."