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sun tracker

simple sun tracking device
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A few days ago, [Bungston] proposed a solar furnace for making charcoal (see ‘Home Solar Charcoal Distiller’), as a means of improving life of impoverished Africans. However without a sun tracking device, his solar furnace would only be in focus for a short period of time. A simple solution would be to mount the solar furnace on a pivoting system which allows manual adjustment of the orientation. However this would be boring and laborious work.

Alternatively, a sun tracking device could be used. A typical sun tracking device comprises 2 motors which adjusts horizontal and azimuthal orientation. Each motor's speed is controlled by a computer which takes into account the latitude, date and time. However such a sun tracking systems are expensive and prone to damage.

I have designed a sun tracking device that requires only one motor and no computer. The design is based on the fact that the sun moves on arcuate trajectories depending on the date and latitude.

A semicircular 'toothed hoop' is manually set at an angle depending on the date and the latitude (a chart is provided to convert the date and latitude into an angle). A cog runs along the toothed hoop at a steady rate, thus tracking the sun.

The problem is to design a fixed motor transmitting rotation to the moving cog. The simplest way to do this is with a universal joint. (See linked pictures - suntracker_universal_joint)

Unfortunately universal joints are prone to wobble and inefficiencies as the angle diverges from the drive axis.

I have replaced the standard universal joint with (my own) trickier version (spherical_gear_detail and spherical_gear_detail_angle). This gear is essentially two spheres, each sphere with meshing ribs. The top cog can be 'rolled' to change its azimuthal angle.

The device is shown in pictures sun_tracker 1, 2 & 3 and sun_tracker_detail at link.

To use, the device is first set to face North (or south depending on which hemisphere you live). The angle of toothed hoop is set with the yellow handle (using the look-up chart for particular date and latitude).

The motor (not shown) drives the near axel. The cog at the end of this axel turns the double-sided toothed ring, which turns the bottom (red) spherical gear which turns the blue cog. The spherical cog system (red and blue cogs) is mounted onto a turning ring (dark green) and can be driven by the double-sided toothed ring from any angle. This allows the spherical cog system to rotate in the horizontal plane (thus tracking the sun from east to west). The top spherical gear (blue) is held in place by a pivoting collar (light green) mounted to the turn table.

I envisage using a gravity-powered motor (like the one used in clocks). The weight would be manually raised in the morning and would fall at a steady rate to turn to produce constant speed. The speed could be adjusted with a variable weight speed governor (The motor speed would need to be adjusted according to the date/latitude)

The solar furnace (not shown) would be mounted on the top brown disc. This could either be a Fresnel lens, Fresnel reflector or parabolic reflector (with object to be heated placed at the focus).

xaviergisz, Nov 28 2005

Home_20Solar_20Charcoal_20Distiller [xaviergisz, Nov 28 2005]

tracking solar concentrator plans http://www.ida.net/...sl/solar/page_i.htm
Last time I read this, there was a legal page you had to read and check OK stating that you understood that focused solar energy is dangerous. [Zimmy, Nov 29 2005]

US patent 305,714 http://patft.uspto....s&Query=PN%2F305714
I'm 120 years too late to get a patent on my spherical gears ;) [xaviergisz, Dec 11 2005, last modified Dec 12 2005]

[link]






       I guess you win the school's science prize! Oh, wait, did you actually build one of these?
DrCurry, Nov 28 2005
  

       I build all my inventions, DrCurry, and I keep them all in my secret bat cave.
xaviergisz, Nov 28 2005
  

       /A cog runs along the toothed hoop at a steady rate, thus tracking the sun/   

       Hang on a minute.   

       /The speed could be adjusted with a variable weight speed governor (The motor speed would need to be adjusted according to the date/latitude)/   

       Ah yes, quite correct. But surely a daily adjustment of hoop angle, motor speed, and weight re-lifting makes things more complicated than the usual, computer-controlled method?   

       Also, I am suspicious that the hoop profile would need to be different for different latitudes and dates, but I'll need some time to do the calcs on that one.   

       I can say for sure that you'd need more arc than a semi circle can offer in the summer months, as the sun rises and sets "behind" the East-West line (which is the limit of the semi circle hoop). The extent of this effect depends on latitude of course.   

       Finally a point on flexible joints. Constant velocity joints are available off the shelf (ball type "CV" joints for instance, plus the good old fashioned double Hooke's joint), and would be more reliable than the meshing ribbed spheres you describe.   

       An honourable invention though.
Texticle, Nov 28 2005
  

       Also just regarding the mechanics, I wonder whether the red shaft would freely rotate due to the movement of the double sided ring. I think it would have a tendency to just move in an arc with the double sided ring, skewing the whole blue shaft/brown part assembly.
Texticle, Nov 28 2005
  

       Texticle raises some good points.   

       This is an *approximate* sun tracker. The purpose is to make charcoal with a Fresnel lens. Being out 1 or 2 degrees on the horizontal or azimuthal direction and it'll still work.   

       I have assumed that the trajectory of the sun can be approximated to arcs formed by the projection of an angled circle. The approximation only needs to hold during the hot time of the day (say 9 til 3). But I'm not an astronomer, so I could be way off.   

       I don't think adjusting the angle of the hoop and speed of the motor and raising a weight every morning is too onerous a task… I mean, If you’re needing to use this in the first place, it’ll probably be improving your life, even with this daily manual labour. Also, just loading the material in and out of the device to form charcoal is, in itself, necessary daily manual labour whatever the sun tracking device used.   

       I considered using a universal joint (a double Hookes joint, see last two pictures). CV joints may be a useful alternative, although I don’t know how they’d cope with the range of angles required.
xaviergisz, Nov 28 2005
  

       I don't know if it's been done before, but I dreamed up a control method to track the sun.   

       I used a sighting tube that allows a "ray" of light to strike a surface inside the tube that has 5 solar cells.   

       The arrangement of the cells would be a 1x3 cell on the top & bottom rows with 3~1x1 cells in the middle.   

       If the top cells are struck by the light "ray" they will initiate a slow sequence turning the dish to a lower azimuth or altitude. When the center cells are struck by the light "ray" they turn off this sequence. If the left cell is activated, the collector is moved to the right until the middle cell is struck.   

       A pretty in-depth set of (low budget) construction plans are shown in the [link] I posted. I have not read through the entire thing yet, though.
Zimmy, Nov 29 2005
  

       A single-motor heliocline (solar plane) transit system is very common in solar collection devices. Nothing new there. Spherical gears are baked. Clockwork mechanisms with a 24-hour period are VERY baked. Putting them together in a non-novel way does not constitute a new idea.   

       An electrically-driven heliocline suntracking mechanism is extremely simple. Let the sunlight shine through a single hole onto one of two solar panels. Connect both positive terminals to ground, and connect each negative terminal to one of the terminals on the motor. When the beam of sunlight is not shining on the two panels evenly, the solar cells will generate different electrical potentials. When properly arranged, this will drive the motor in a direction to re-center the beam.   

       If your system is too heavy to be driven by the slight voltage difference, the signal can be fed to transistors driving a wheatstone bridge circuit.   

       Simple, cheap, effective.
Freefall, Nov 29 2005
  

       What [Freefall] said. Personally, I've always felt that the most elegant solution to this problem would involve using thermal expansion somehow.
Overengineered, complicated, expensive, plausible [+]
An incredibly boring and unamusing subject to devote your overactive imagination to [-].
moomintroll, Nov 29 2005
  

       Grow sunflowers on the same surface that the tracker sits on, tie string around the heads of the flowers and let them tug the device around as they follow the sun.
fridge duck, Nov 29 2005
  

       [fridge duck], you are on track here...
normzone, Dec 12 2005
  
      
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