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(Original author: NVsion – www.nvision3d.com )
Evernham Motorsports is using NVision's ModelMaker laser scanning system to develop its racecars more quickly by allowing the team to document even the smallest changes to the body design. The major components of the Model-Maker system are a 3-D laser sensor, a mechanical digitizer on which the sensor is attached, a PC, and software that extracts, displays, and manipulates the data.
In automobile racing, where as little as 1/100th of a second difference in lap time can mean the difference between first and second place, slight variations in body design have a huge impact on performance. Teams work hard to optimize the car's shape for the best aerodynamics, but until recently, they had no way of precisely documenting that shape.
According to the NASCAR rules, all vehicles have many of the same components, including the transmission, steering gear, suspension, electrical, and fuel system as well as brakes. The chassis are also basically the same, a front-steer-type built by one of three major chassis builders: Laughlin, Hopkins, or Hutcherson-Pagan. The car bodies are tightly regulated by NASCAR. The acceptable shape is outlined by templates, 2-D silhouettes defining certain longitudinal or lateral cross-sections of the body. The templates include acceptable tolerances, which can be as much as 13 mm (0.50 in) or as little as 1.8 mm (0.07 in). Although the tolerances have been tightened in recent years, some latitude is given that allows for alternative body shapes that still fit within the scope of the NASCAR rules. As teams have become more knowledgeable about vehicle aerodynamics, for example, they have begun using the tolerances within the body templates to their advantage, fine-tuning the car's exterior to minimize wind resistance as much as possible. These slight variations in body design have had a huge impact on performance. Since these changes are very minor, documenting them with a great deal of precision is a necessity.
After the team built a prototype of the new Dodge Intrepid, Evernham Motorsports engineer Tim Malinovsky recorded the shape by simply holding the laser sensor so that a line of laser light appeared on the body. The ModelMaker uses a single viewpoint laser stripe sensor. Laser stripe sensors, which are significantly faster than simple laser point sensors, work by projecting a line of laser light onto the object while a small CCD camera views the line as it appears on the surface.
The mechanical digitizer moved freely about the body, allowing Malinovsky to position the sensor easily and capture data rapidly and with a high degree of resolution. As he moved the sensor over the surface of the body, a dedicated interface card translated the video image of the line into 3-D coordinates. These data are combined with the Cartesian and angular coordinates generated at each position of the mechanical arm. The result is a dense cloud of 3-D data describing the surface of the object. A laser scan of an entire car body usually generates 25 million 3-D coordinates and can be done in 12 to 14 h.
Once the coordinate data were acquired, the team sent the scan data to Dodge, which also uses an NVision system in its development efforts. Dodge imported the data into its CAD system, CATIA, scaled it down, and used it to produce a 3/8-scale clay and fiberglass model, which was then tested in a wind tunnel.
Evernham Motorsports also used the scan data as a precise record for tracking aerodynamic improvements. An original scan served as a record of the baseline shape. Then, as the prototype body was modified to improve aerodynamics, the scanner was used again to quantify these relatively minor adjustments, enabling them to benefit from the lessons learned on the vehicle's aerodynamic performance.
Download: Evernham Motorsports uses handheld scanner (PDF file)
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