Saturday, January 27, 2007

motor drive mechanical 1

Aiming the entire solar heater array toward the sun is done with one very small and low current 12 volt DC (direct current) gear motor (mounted in the green box). The gear motor output shaft is coupled to a 1/2 inch threaded galvanized steel rod on which rides a small yoke. In the yoke is embedded a 1/2 inch hex nut. As the motor turns the threaded rod, the yoke travels along it. The yoke has a threaded stud on top (pointed toward you in the picture) and two small steel wheels. The wheels run along the wooden beam and prevent the yoke from rotating.

The stud on the yoke couples it to a steel actuator arm (the rusty rod running up at a slight angle) which drives the end of a 1/4 inch steel drive rod that runs down the entire length of the array, under the collectors. Each collector is coupled to the drive rod through an aluminum arm and an eye bolt.

As the threaded rod turns, the yoke travels along the shaft and pushes or pulls the collectors into position via the drive rod.

Two limit switches (seen along the bottom edge of the wooden beam) sense a small magnet on the lower wheel of the yoke to tell the electronics to stop motion at the east or west limits.

Here is a close-up (click to enlarge). The arrangement is such that the collectors will rotate through about plus or minus 45 degrees, thus catching the sun's hottest rays at mid-day.

The overall gear ratio is about 6000:1. You can see the shaft turning about 12 revolutions per minute when the motor runs, but you can barely see the motion of the collectors.

The motor drive wooden beam is positioned at about the mid point of the collectors and drives them through the aluminum arms attached to the middle rib on each.

At this stage, I had not put a concrete footing underneath to support the motor drive so I had suspended it between the ends of the array on a wooden cross piece. It flexes a bit, but is solid enough such that it worked well for the first season.

At each collector, two small coil springs and two collets on the drive rod provide a bit of decoupling to keep the wind from buffeting the motor. The eye bolt can rotate because it is fastened with an aircraft nut at the back which is not completely tighted on the eye bolt's thread. If you can picture the drive rod moving away from you into the picture, the front collet forces the spring against the eyebolt which pushes the collector aluminum arm away from you. This action will rotate the open face of the collector towards you in this illustration.

The collets can be loosened and the position of each collector adjusted by sliding the collets and springs along the drive rod and then re-tightening. In this manner, each of the collectors can be adjusted at installation so that they all point in the same direction.

You can see that the drive rod has already started to rust. I intend to replace it with one made from stainless steel. Otherwise it will soon be impossible to adjust the position of the collets on the shaft. Interestingly, the collets which are supposedly not stainless, are holding up rather well with the exeption of the set screws.

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