Sat Mount Conversion
A key part of our renewable energy strategy involves repurposing various already available pieces of equipment rather than starting from scratch. Now that the small high-frequency home satellite reciever has taken over, the lower frequency home satellite dishs are obsolete. Many have been taken down, but there are still a lot out there that can be had for scrap value. This article is about reworking a satellite dish into a solar energy receiver.
The picture above shows an eight foot diameter spun aluminum dish. The photo was taken just before the morning walk the day after Camile had finished removing the flat-brown paint that had covered the dish, thereby making it reflective again. It you look close at the center of the dish, you can see a white plastic shrowd covering the out-dated electronics.
While we were on the walk, the sun passed over the dish melting the shrowd and frying the electronics. That wasn't a direct hit since if it had been, the heat would have melted more than the plastic since this size dish is able to focus five kilowatts of heat on a small area. We quickly swung the dish around so that it will face northward and away from the sun until it's ready to be put into service.
A key step in that process involves reworking the mount that controls where the dish is pointing. Home satellite dish mounts are designed to allow the dish to focus on the band of geosynchronus satellites that orbit some 23,000 miles above the equator. What we want the dish to be able to do is to track the sun from horizon to horizton, summer and winter, which is a bit more of a challenge.
The first dish we want to modify is our larger 10 1/2' diameter dish since that will capture about 7 kilowatts of energy by virtue of its larger surface area. With that added size comes a lot of added weight, so the first task involves reworking the mount to carry that weight as the dish rotates from east to west during the day.
The mount is built around a length of 4" steel tubing that slides over a length of a slightly smaller pipe that's been cemented into the ground. In the picture you can see a steel strap welded across the top of the mount; this supports the satellite mount on the smaller, interior supporting pipe.
In a geo-sync configuration, the 4" pipe rotates around the interior supporting pipe as the dish is initially aligned, and then it's permanently secured to the supporting pipe. The goal of this modification is enable the mount to rotate smoothly around the interior support pipe as the dish rotates to track the sun each day.
The key to doing that involves inserting an axle and bearings in between the mount and the support pole.
the alignment bushing and the axle
The axle has to be mounted on the support pipe, and we needed an alignment bushing to hold the axle in the center of the support pipe. To make the bushing we first drilled a hole in a piece of one inch thick plate steel. We then mounted a bolt through the hole and chucked that up in the lathe to turn the outside to the dimensions we needed.
First we machined the outer dimension to be the same as the outside diameter of the support pipe. Then we machined away enough metal so that the lower half of the bushing was a snug fit against the inside of the support pipe.
There are two sets of tapered bearings that support the hub as it turns on the axle. The critical bottom bearing is shown mounted on the axle in the pic below; it's what will carry the weight of the mount, the dish and the counter-weights.
the alignment bushing with a short length of 1 1/4" pipe welded on
The next step involved creating an interior support for the axle made from a lenth of 1 1/4" pipe and a standard cap. The pipe was cut to the length needed to support the axle so that the hub would spin freely when the mount was installed on the support pipe.
The hub was then welded onto the original mount, using the lug holes to align the hub with the pipe.
The last step in this stage of the conversion involved welding the main support arm perpendicular to the main pipe.
Notes From Windward - Index - Vol. 71