Fig. 2-16: TETRIX robotic kit. Although the use of TETRIX components reduces the effort and time required to design and build the system, not all of the components were initially available. Thus, the arm needed to be designed before the components were acquired. The Solid Works CAD tool was used to accomplish this. Solid Works is a modeling and simulation environment capable of representing three dimensional shapes in space in addition to material properties. An online CAD library was used to acquire models of most of the TETRIX and LEGO components. These individual models are combined in an assembly that defines the spatial and kinematic relationships between them. The resulting virtual assembly is used to evaluate the moments of inertia, mass, volume, physical dimensions, etc. at a component or system level. Also, this assembly is used to simulate motion between the components. This allows the designer to check for collision between parts, analyze the range of motion of the entire system, and visualize its performance before anything is physically made. Approximately eight design iterations were investigated with this tool before parts were ordered and very little was changed from the CAD model once it was actually built. Figure 2-17 shows the final model of the arm without any custom fabricated parts.