Conceptual Design

The conventional design process for a vehicle prototype begins with an artist’s concept, often in clay. Designers then measure and model it, package subsystems, and then patch and refine the design of both the body and subsystems until the design can be recommended based on estimates of acceptable performance, producibility, and cost.

Our team followed a tougher path. Form was constrained by the early choice of a preexisting, two-seat, carbon fiber-reinforced composite body. While local availability of this subsystem reduced development risk, it also limited the type and number of design changes greatly. Since we also chose off-the-shelf solutions for large systems like the engine and motor/controller, most changes to the vehicle design during packaging and analysis had to be accommodated by the frame and transmission.

The body choice also came with crude IGES wire frame data digitized from a small wooden mockup. With this surface curve data in hand, the lead designer generated surface quilts that would be successively refined into a realistic solid surface model of the thin, complex body geometry. Early modeling productivity and the seduction of visual representations of this early body swayed the project leadership away from competing choices—and from the temptation to abandon PTC tools in favor of a comfortable build-test fix approach.

Pro/SURFACE ® was used to convert the IGES file into robust Pro/ENGINEER ® datum curves and then surface quilts. Quilts were constructed in sections using the surface by boundaries method. Local tangency conditions at quilt intersections were adjusted using Pro/ENGINEER’s datum curve analysis package. Dihedral angles and datum curve accelerations (determined by porcupine displays) allowed the design lead to create the necessary tangency conditions appropriate for the seamless intersection of all the quilts. Individual quilts were merged to form a single, continuous quilt. The protrusion-thin-quilt method was then used, and a final protrusion with an assignable thickness property was now available to calculate mass property, as well as surface and frontal area. Expected vehicle performance was again verified using the new information.

The Pro/ENGINEER body model provided a base feature for virtual packaging, allowing team members to move forward with the design cycle at an impressive speed. A rapid prototype of the body geometry was created to disseminate the team vision. Pro/ENGINEER’s STL file format was used to produce a 1/16-scale stereolithography model. This tangible artifact enhanced design reviews by allowing team members with little modeling skill to interact with the body design database a full year before fabrication began.