Mother's Solar Tracking System

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DOIN' IT

The tracking system for our solar furnace is actually quite simple ... once the electronics are worked out, the mechanical assembly is a snap. Start by drilling and tapping the ends of your 1/2" X 2-1/2" machine bolts to accept 1/2" X 1/4-20 bolts, then drill three 1/4" holes through both of your 3/16" X 4" X 16" steel plates where the pulleys are to be mounted. (it'd be a good idea to line the plates up evenly and clamp them before you drill ... that way, the holes in both plates will be in alignment.)

Now, merely enlarge the holes in one plate to 1/2", slip the bolts into these holes (shafts up), and weld them from the bottom. With that done, fasten the 6" V-pulley directly in the center of the large sprocket with four 1" X 1/4-20 bolts, then wrap the chain around the large sprocket, slip your lower spacers over the appropriate bolts (the 1/4"-high spacer on the "main" shaft, and the two 7/16" spacers on the other two "auxiliary" shafts), and slide the three pulleys in place as shown.

Before you install the final spacers on the shafts and bolt down the cover plate, take your small 16-tooth sprocket and slip it over the gear on the drive motor ... it should fit snugly, and you can lock it in place by running the setscrew in the sprocket hub between two gear teeth. Now run your chain around the small sprocket, and mount the motor to the plate so that the chain is taut (you can cut the chain to the proper length if necessary). Finally, fasten the cover plate to the top of the pretapped bolts with the spacers underneath. From there, all you have to do is mount the drive unit to an appropriate strut on the support frame and thread the rope through the large V-pulley.

The housing that shrouds the phototransistor (and subsequently triggers the drive motor on and off by casting a sharply defined shadow on the sensor after the mirror frame has moved slightly) can be made from a 3" X 9" piece of thin sheet metal. Bend the sheet at a 90* angle down its "lengthwise" center, and then cut an inch off the end of the metal to one side of the bend. Now, take the inch-long "tab" that's left at the "cut" end and bend it again, at a 900 angle-over towards the inside of your newly formed "box"—creating a sharp edge that will cast a shadow when the sun is shining on it. Repeat this procedure at the other end of the box (but this time, only cut 1/2" off the end) and fasten the perfboard and phototransistor to this smaller "tab" with a short bolt.

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