Have you ever been sitting in the shade and thought "I wish the sun could come to me
"? Well now it can
I wanted to squeeze some extra sunlight into my life to provide some free heat as well as reduce the risk of the Crabby-McNasties
. There is a wonderful device called a heliostat which can reflect those powerful sun beams exactly where you want them; as in "pew pew pew". UPDATE JULY 18 2013: I have been contacted by a real professional (see "redrok" in the link and comments below) to advise me that I have oversimplified the geometry causing errors in aiming. I didn't get the calibration and tightening up to realize that I had this problem before Icarus died of a blown motor. Please see the next step for more details of where I went wrong (Rectilinear vs. Spherical Geometry).
A heliostat is basically a mirror that rotates to reflect sunlight on a fixed point throughout the day: into my dining room in the winter or onto a solar pool heater in the summer. This seems like a very easy project until you consider that there are two axes of rotation, and that the sun's position in the sky changes with the seasons (hugs the horizon in winter). I've been wanting to build a heliostat for a few years, even though I have never actually seen one (until today!). Heliostats are commercially available, although they are not quite mainstream yet. There are many hobbyists trying new and innovative ways of working out the geometric and mechanical challenge of splitting the angle between the sun and target:
Using clockwork: http://www.instructables.com/id/HELIOSTAT/
Using Arduino to calculate where you need to point: cerebralmeltdown.com
A complete history of Heliostats: http://www.redrok.com/main.htm#mechanical
Commercially available: http://lightmanufacturingsystems.com/order/
I am quite certain that the best solution is to have some form of computer that calculates the required position of the mirror and transfers instructions to precise actuators or step motors to position it in real time. Arduino appears to be sufficiently powerful, and the necessary code is mostly available in some form. This is where the "ANALOG" comes from in my title: I was looking to bypass the computer and precise motors to A) reduce the cost, B) make it more weather-proof and C) make it trouble-shootable (for a lowly geologist like myself). So, although I am using electricity and electronics, this is more like your grandmothers radio (analog) than you might think. I don't expect that this design would be rolled out in the western world, but the relatively simple mechanics means that it could find a niche hobbyists and in developing countries. In fact, much of the body and mechanism would lend itself well to 3D printing (future update?).
I was inspired by the many Arduino Solar Tracker
projects which seem to handily provide a vector to the sun. The second vector of interest is straightforward: it points directly towards the target (window, pool heater). To get the sun reflected where you want it, the mirror needs to be positioned perpendicular to the bisector (exactly half way, or normal) between these two vectors. That seems easy, right? A simple computer or child can tell you where that bisector is; neither of which I know how to provide instructions in a form that would be executed. The point is: I am trying to eliminate computer processing from the equation, so how do you precisely split an angle in three dimensions "mechanically"? See the next step to see my low-tech solution. If I have just invented (or not) the equivalent to a "square wheel" (as in, a more elegant solution exists) please let me know in the comments below.