It is trial and error and it will change a LOT before I can include it in the instructable.
I really hoped that someone else would do this and save me the trouble. I might not have time to use it but hopefully the pictures will explain what I am trying to do.
I am 99% sure that it will work well. (If not for me, then for someone with greater technical skill).
A great Austrian humanist called Wolfgang Scheffler thought up a new design for a solar concentrator while daydreaming in university class in Germany. He could not afford to make his design a reality in Germany or Austria so he left for Kenya (and its different labor and price structure) and after about 2 years the design became reality. It is still something they can make cost effectively in Kenya but not in Germany. As soon as he built the first one, he was asked to build another and pretty soon he was asked to help design more in India. So off he went and now there are thousands of Scheffler solar kitchens in developing countries around the world! But very few in rich countries due to subsidized fossil fuels here.
Basically Scheffler solves a problem with seasonal adjustment of parabolic dishes by warping the dish dish a little every day and effectively making a new parabolic dish every day as the sun's path changes with the seasons! His dish is on equatorial mount and turns at 15 degrees per hour (Just like telescopes following the sun).
Basically the task here is to design a parabolic dish that works on equatorial mount but does not need to be a shape changer. If we can do this we can have powerful effective parabolic solar cookers stamped out by the millions for next to nothing by the type of machine that turns a piece of metal into a car body.