【正文】 rials from the previous structure (which was also intended to be a uniaxial tracker) in construction. Another more plex concept was to track the sun biaxially which would involve tracking the sun both east to west and throughout the seasons. The advantage of this concept was a more efficient harvesting of solar energy. The third concept was to only track throughout the seasons. This would provide small efficiency gains but nowhere near the gain provided by tracking east to west. The different structures we came up with to acplish tracking motion included a rotating center axle with attached panels, hydraulic or motorized lifts which would move the main panel in the direction of the sun, and a robotic arm which would turn to face the sun. The clear efficiency gains coupled with the simplicity of design of the uniaxial tracking system and the existence of usable parts (. motor and axle) for the rotating center axle structure, led us to the choice of the East to West tracking, rotating center axle concept. Structure Once the method of motion was chosen, it was necessary to generate concepts for the structural support of the axle. Support could be provided by the triangular prismatic structure which was attempted by the previous Smart House solar tracker group or through the use of columns which would support the axis on either side. While the prismatic structure presented the advantage of mobility and an existing frame, the columns would have provided us with ease of construction, simple geometric considerations, and ease of prospective mounting on the roof. Due to the heightened intensity of time considerations, the previous financial mitment to the prismatic structure by Smart House, and our limited budget, the presence of the preexisting frame proved to be the most important factor in deciding on a structure. Due to these factors we decided to work within the frame which was provided to us from the previous Solar Tracker group. Tracking Motion Once the structural support was finalized we needed to decide on a means to actualize this motion. We decided between sensed motion, which would sense the sun?s position and move to follow it, and continuous clock type motion, which would track the sun based on its predetermined position in the sky. We chose the concept of continuous motion based on its perceived accuracy and the existence of known timing technology. During the evaluation stage, however, we realized that continuous motion would prove difficult. One reason was the inability to draw constant voltage and current from the solar panels necessary to sustain consistent motion, resulting in the necessity for sensing the rotation position to pensate. Continuous motion also required nearly constant power throughout the day, which would require a mechanism to store power. Aside from these considerations, the implementation of a timing circuit and location sensing device seemed daunting. After consulting Dr. Rhett Gee, we decided on a device using two panels and shading for sensed motion. 4. Analysis and Embodiment Structure Geometry The geometry of the frame was created in order to allow the solar panels to absorb light efficiently. This was done by allowing rotation in the eastwest direction for tracking the sun daily and a 36176。 inclination (Durham?s latitude) towards the south. Because this frame was designed to be placed on a roof with a slope of 25176。. The geometry of the existing platform structure was modified. This was done in order to incorporate the results from the Clear Day Model supplied to us by Dr. Knight. This model led to the conclusion that the platform should track to up to 60176。. Also, crosspieces were moved to the inside of the frame to allow greater rotation of the platform before it came into contact with the support structure. The panels used for sensing and powering rotation were placed on the plane of the platform. Mirrors were placed perpendicular to and in between the panels to shade one and amplify the other in order to produce a difference to power the motor. The sensing panels were placed outside the platform area to maintain the largest area possible for collecting panels. A third sensing panel was mounted nearly vertical and facing east to aid rotation back towards the sun in the morning. This panel was attached to the frame under the platform, so that during most of the day, it?s shaded with minimal effects on sensed rotation. Minimizing the torques on the motor was a main concern in order to minimize the motor power needed. The platform designed for the placement of the collecting solar panels was placed under the rotational shaft so that the panels would be aligned with it the rotational axis. Since the main panels prise the majority of the weight putting these in the plane of the rotational axis reduces torque on the shaft. The sensing panels were placed symmetrically about the axis of rotation in order to prevent additional torque on the motor. The third panel was attached to the frame instead of the platform or rotational shaft so as to also avoid any torque. Materials Materials selection for most of the frame was simple because