Tracking the sun Big Time
Tracker Version 1
The big hurdle that many people have when thinking of converting your old big dish into a solar furnace, is how to make it follow the sun.
First thing you need is a base, I welded up a triangulad base from heavy channel. The front wheel bearing from a VW bettle was attached to a large 1/4" steel disk.
Once the disk was mounted to the wheel hub, the disk was rotated and a line drawn at the largest continuous circle that would fit.The steel was trimmed to the line, with hand jigsaw, and finished with hand grinder.
I wanted a chain drive, so I turned the big disc into a giant sprocket in a crude but effective way.
I took a #40 chain, and wrapped it around the big disc. I used a center punch and marked the disc edge each 10 teetk of the chain.
Uf course, it did not come out an even number of teeth, so I made a single tooth add on to the disc to exactly keep the chain in place simulating the correct diameter so the teeth exactly match around the diameter. I drilled and tapped a 10/32 hole at each punch mark, locktited a 10/32 threaded rod into each, and cut off the lengths and deburred and shapped the teeth and it worked beautify.
Tracking is really pretty simple,especially if it is kept in the analog world. Never underestimate the lowly Op amp, and a few power transistors in a full bridge servo amp.
The sensor is something I invented 20 years ago, that is the magic in the self powered solar tracker below.
Two photo sensors are configured so the two detector outputs will cancel to zero V when both have equal angle/illumination from the sun.
Photo diodes or chips of solar cells work well as photo detectors. I set them at 45 degrees to each side of where I want the null to be. The ones I used on the big dish are set in epoxy putty.
The first drive system has the horizontal axis powered by a precision harmonic drive gear motor that is way too expensive for a dish,but was in my surplus motor box.The vertical axis with just a simple wench, is very balance sensitive.Any imbalance against gravity has to be constantly provided by the motor to hold a position. Weather protection for a chain is too difficult.
I found some nice C band big dish satellite movers for $39, and they are waterproof and since they are an acme screw drive, do not need to provide much holding force even with a big weight imbalance.
The new motors will be put on the system in the spring.
A schematic of the basic tracker is available on the downloads page:Simple Tracker schematic
The photo detectors I used were osram BPW34FA which are available from digikey