This is a word description describing the construction steps of the Batant (SFT Training Model). When refined and complete (hopefully with help from your feedback, leave a comment or email eerik(at)solarfire.org directly) I will make a new pdf will be made containing the descriptions. The original guide is meant to be understood without words (and so in every language), but words can be helpful.

Introduction

This is a training guide to become familiar with the Solar Fire Technique and build a small demonstration and experimental model.

It should be kept in mind that the advantage of this technique is in building far larger machines (9 meters squared and beyond) since no parabolic bending of steel or precise tools are required, which are limiting factors of large parabolic concentrator construction. However, at the small scale, such as the around 1 meter squared of this model, a single parabola may be easier to build than this technique.

Because it is a training model bolts have been favoured over welding so that mistakes made can be more easily unmade and also so the entire machine can be disassembled into the smaller pieces for transportation. However, if you are confident in welding and have no worries about piece size, where more welding is convenient is mentioned as under the alternative headings in the step descriptions.

Page 1

This is the general plan of the entire machine, that gives an understanding of how all the components fit together, which we shall see each in turn. Only 4 reflectors are shown simply to not clutter the drawing, 12 (4 on 3 rows) are necessary to complete the machine.

Page 2

The Mast is the vertical structure of the machine which rotates around the base, and is constructed first.

Page 3 The central component of the Mast is the Key, which allows the Post to rotate on the base.

Two corresponding nuts are placed on our large bolt (minimum 1cm diameter), two “wings” of corner steel (or angle iron) are cut with two holes (6 – 10 mm) near the bottom of each. Everything should able to be held together nicely as seen in the last image. These nuts will allow rotation around the bolt.

Alternative: The alternative to the Key method is the “Tube in Tube” method, where one tube simply rotates inside another. However, in the authors experience finding a tube that fits flush inside another is far more difficult than finding a large bolt, and in any case the Key method has the advantage of being lighter than the “Tube in Tube” method. On paper Tube in Tube might seem simpler than the Key, but (without a tube cutter) it’s actually more difficult to cut a tube completely completely flat than it is to weld bolts to the Wings in the next step.

Page 4

The next step is to weld the Bolts to the Wings. The nuts must be on the bolt to ensure correct alignment so the key will be able to rotate on the bolt (which itself will be welded to the base). Holding everything together in a clamp is a probably a good idea. What’s not shown in the drawing is that it’s helpful, if not necessary, to cover the threads of the bolt with tin or thick fabric, to ensure droplets from the welding does not fall in the threads. The bolts can then be welded to the Wings and pieces of flat steel welded on top for reinforcement.

Alternative: If you don’t have a metal clamp, it is possible to hold things together between 2 pieces of wood.

Page 5

On the reverse side, the bolts can (most likely must) be reinforced as well. Bellow and above these reinforcements to other flat steal pieces must be drilled with (smooth or threaded) holes (6 mm diameter) and welded to the wings.

Note: to be smooth for many years, and decades, it’s a good idea to oil the key from time to time.

Page 6

The Base Beam will connect the Frame to the Post. At the ends connecting pieces (a square of angled steel with holes must be fitted). In the center holes must be drilled to connect the Base Beam to the Key. The easiest way is to first measure the distance between the holes on the Key, say 3.5 cm, then mark the center of the Base Beam, then off set the marks for the holes by half of 3.5 cm (1.75 cm), so the key will be centered. Drill one hole, then pin the key to the Base Beam with a bolt through this very same hole. Then straighted the key and drill through the opposite hole. This will ensure that the holes on the Base Beam are perfectly in line with the holes on the Key.

Alternative: The end pieces (used to make a “boxed end”) can be welded. Using a bolt to connect the boxed end to the Base Beam, is used for the sole reason that the Boxed End can be changed if ever a mistake was made in measuring. The Key could also be welded to the Base beam, but again if a mistake is made it will be difficult to remove the key, but also it’s more convenient in the long run to have a key that can be detached.

Page 7

The Base can be easily made with angled steal and welded together. It is important that the base is as flat as possible (welding can easily bend the connections, so it’s make everything sturdy before welding), and the bolt as vertical as possible.

[Mistakes in img: the circle of the cut out is inverted, there is an extra line in the base.]

Page 8

The Post is simply a box tube cut at 1 m length with holes drilled as shown (all right through both sides). The third hole from the top is simply to fit a Hook which will hold our cable.

Alternative: A round tube could also be used (for instance with the “Tube in Tube” method), but box tubing is more easy to work with. Essentially anything can serve as a hook, even a bolt straight through and using twine to tie around the cable and post (so the cable does not slip).

Page 9

The Target will hold our pot. Again, for connecting to the Post, the method of drilling one hole, bolting, and then drilling the next can be useful. Flat steel is relatively easy to bend and twist, and since this piece is easily removed it can be refined later (if slanted to one side for instance).

Notes: It’s important that the first bend is not too close to the holes, which will make it impossible to bolt to the post (a bend must always clear the surrounding pieces, which can be tricky if they will be attached later).

Alternative: The method above has the advantage of being easy to build. Many other methods are possible. For strength, box tubing or angle can be used for the connection with the Post (as the principle of leverage will place much force at this juncture); for the Prometheus-12 heavy pots are unlikely to be used, but for larger models strengthening can be a good idea. Many methods also exist to clear as much as possible the bottom of the pot, so a maximum of heat is absorbed (no energy is transferred to the Post).

Page 10

The Frame is attached to the Post and will hold all our reflectors. The only moving parts of the Frame are the handles which have a swinging movement. The side pieces will form a single fixed piece.

Page 11

These are the sides of the machine that will hold the rows. The bolt that attaches the two pieces of each side must be extremely tight; adding another nut to block further the first nut adds extra strength. This connection bolt can be 6-10 mm.

Alternative: To add more power to the machine, the lower pieces can be cut longer (25 cm) and a fourth row added. However, since this is a design only for training and demonstration, and adding the fourth row obliges either welding the joint or adding a triangle support (next paragraph), a 3 row design was kept.

Again a bolt is used to attach the lower and upper pieces in the event of a mistake and so the the machine be taken apart to the smallest possible pieces for ease of transport if necessary. Once the machine is finished and working properly this connection can be easily welded solid. If, on the other hand, the small pieces is desired, then this connection can be strengthened with a cable or flat steel piece forming a triangle with the two pieces to make it stronger than the bolt method (which is not very strong).

Or, the main side piece can be cut longer and bent in the way described by cutting out a triangle, bending and welding, to form one piece. This method is only recommended to experienced metal workers, or after once you already built one machine with success.

Page 12

This piece is simply for stabilizing the machine, it connects the tops of the two sides to keep everything square.

Page 13

The rows only require holes.

Alternative: The holes that will hold the reflectors (all the holes except for the far ends) can be threaded (tapped) so a bolt can attach the reflector arms directly to the rows without use of a nut. This makes attaching the reflectors far easier as only one wrench is needed rather than two (one for the bolt and one for the nut). Rigorously speaking, if the threading method is used, then drilling right through the box tubing is not required, as a single a hole on one side is enough to make a threaded hole. However, depending on the quality of your box tubing (and skill threading holes), some of the threaded holes can be easily stripped later requiring going back to the straight-through-nut method. So, either prepare to take the row off and drill right through the stripped hole, or drill right through all the holes preemptively. If you don’t know how to add threading to a hole (create a nut directly in the metal) then you may forget this alternative (using two wrenches is not impossible and once the machine is mounted it stays that way for some time, and even when dismounted the reflectors can be taken off the arms, leaving the arms in the correct position on the rows).

Page 14 Though it seems like all this bending to make the handles is a lot of work, it serves two significant purposes. First, it allows all the width of the machine to be some 20 cm shorter (with straight handles, the machine must be widened so they can clear the exterior reflectors). Though 20 cm doesn’t seem like a lot, we have to multiply it by all the lateral pieces (3 rows plus the main beam and the stabilizer multiplied by 20 cm will add 1 m of steel). Second, the bend will stop the row from being able to rotate all the way around (the sun is always somewhere above the ground so the rows never have to be inclined to far forward or backward); so this impedes the possibility of the reflectors hitting the ground (this safety catch can be welded onto straight handles, but this design is far more elegant).

Page 15

The right swings for the rows simply attach the rows to the sides. This connection must be free rotating so a bolt with two blocked nuts (turned into themselves, and not against the steel) will keep the bolt in place and allow free rotation.

Alternative: Again this piece can simply welded to the rows, but the bolting is proposed in case you fear a measurement mistake.

Page 16

This piece will extent the sides to allow the cable to clear the reflectors and hang on the main post to support the frame.

Alternative: this piece can be welded to the sides. Or, the side pieces can be cut longer and bent in the way described by cutting out triangles, bending and welding.

Page 17

Here are presented all the 12 final reflectors each from a side view.

Page 18

The long twisted piece is call the arm and the small connector is the hand.

Alternative: By threading (tapping) the arm connection to the hand, a nut is no longer required.

Though it seems corner steel is an easy way to get a 9 degree bend, this piece is very small and it will be difficult later to manipulate the bolt that attaches the hand to the arm (it must be adjusted finely to calibrate the machine). So an alternative design is to shorten the arm by a few centimeters and bend a a longer flat steel piece for the hand, or weld an extender to the corner steel piece described above.

Page 19

The primary reflector starts with a board 30 by 30 cm, with 9 equal squares, 10 by 10 cm, drawn with a pencil. The three marks in each square must be outside the center of gravity of the mirror we will place later. Screws are also necessary for the center mirror to give 2 mm clearance off the wood; this clearance will allow the side mirrors to be tilted to the side (not only inwards) and the center of the inner side of the side mirror aligned with center of the corresponding side of the center mirror. Since these primary reflectors will be used to make molds to make many more copies, it’s worth it to strive for perfection in creating the molds. We then drill 2-2.5 mm holes through all marks and then flip the board and screw our 3mm screws through the opposite side so all the tips come through the side of the board with the squares drawn (this will simply help a bit in positioning the mirrors later; you may find yourself redrawing your squares on the other side if you forget to flip the board). The screws in the center square must be about 2 mm off the board, and as flat as possible; the easiest way is to place a mirror on the screws and look from the side if it seems to be flat and about 2mm clearance (total perfection is not required since calibrating the other mirrors is the critical part). The important thing for the rest of the screws is that they can be easily turned (so screw further out and then screw back in if they are too hard to turn). Then a mirror (10x10 cm) is glued to the center square, using normal glue, epoxy or polyurethane. If you use a glue that tends to expand then place some wait on the mirror at the glue dries.

Page 20

For calibrating the primary reflectors it’s necessary to mount the structure of the machine, and a board or cardboard at the target, to see the reflections (you can draw a square in the center of this board and simply tie the board to the target as it’s a temporary structure). The machine must face directly the sun at all times, this is achieved by observing the shadow of the machine (if you mark the center of the top row with twine or tape, then the machine faces directly the the sun’ with the shadow of the post crosses this mark). Then place by hand primary reflector board a the top corner, and reflect the light of the sun onto our target. Then place a new (10x10 cm) mirror on the first position on the board and hold it against the screws by hand, then adjust the screws until the reflection of this new mirror overlaps the reflection of the central mirror at the target. Repeat for all the other mirror positions and make sure the inner edge of each mirror is as flush as possible with the edges of the center mirror (to avoid a difficult mold).

Important: Remember to mark somewhere on the board the position number it corresponds to as well as the orientation (though the orientation isn’t crucial it helps to preserve it).

Alternative: A strong adhesive like resin and fiberglass or polyurethane is necessary to make the final reflectors. If such an adhesive is lacking and only a weak glue, such as wood glue, is available then these primary molds can serve directly as final reflectors. However, since they are no longer being copied perfection is no longer required, the center mirror can be glued flat to the board and only two screws need to be used for each mirror. The board should be as thin as possible to reduce weight. To attach the board to the hand there are many possibilities.

1 Permanent: the hand can be welded to a piece of tin and then this piece of tin screwed to the board, and any tips that protrude the other side filed or grinded off.

2 Not permanent, a 6 mm hole can be drilled in the center and on the upper face of the board, where the mirrors will be glued, this hole can be widened 10 mm just enough so the head of a 6mm bolt can hide below the surface of the board; then a bolt can be glued into this hole with wood glue mixed with a bit of sawdust; the bolt that protrudes from the under side can attach to our hand (which will require another hole) using a nut.

Either of these methods can also be used to attach the primary reflector board (for making a mold) to the machine to make calibration easier. This can be especially useful in larger machines that require more molds and higher perfection for commercial reproduction. Page 21 When the primary reflector is calibrated all the screws are exactly as they should be, but the 8 outer mirrors are not attached (as they were simply held against the board by hand). However, since our screws are placed outside the center of gravity of each mirror, when the board is laid flat on a table all the mirrors will stay flat on the screws (no need to glue them). The next step is to build a box around the mold and then fill the box with concrete.

Tips: Tape can be put down between the mirrors (to avoid any plaster dripping between them) and around the inside edge of where the box and mirror meet for the same purpose. This does not affect the mold since anything added to the surface of our primary reflector will become a depression in the final mold (as long as a majority of the surface of each mirror is flush against the mold all is well). However, anything that leaks into our primary reflector will become a bump on our mold (and so changing the inclination of the mirrors placed on them), and such bump will have to be scraped off, hence the tape to avoid any plaster leads.

Alternative: Concrete will also work but tends to bond to the mirror surface, so separate the concrete from the mirror with a layer of plastic bag or something; concrete will also be much heavier so is not so suited for mailing the molds but is essentially indestructible on location.

Page 22

Once the molds have been made and are dry, new mirrors are placed face down on the mold and fixed together. In the image a strong adhesive of polyurethane is used since it is the easiest product to work with (no mixing of chemicals, not too liquid). However, be sure to wait the time necessary for solidification, up to 1 day.

Alternative: Resin and fiber can be cheaper, especially in large quantities, and allows for the use of thinner mirrors since the resin fiber will provide structure. With thicker mirror, thin strips of fiber can be placed over the mirror joints (saving a lot of fiber and resin), but with thinner mirror a whole sheet of fiber should back the mirror for strength. 2 layers may be necessary, and further layers may be necessary to fix the attachment piece in the center (the hand) since the whole weight of the reflector is on this piece. Ideally natural resins and fiber can be used (resin extracted from the destructive distilling of trees … using solar concentration perhaps).

Page 23

This page does not exist yet but should show how the whole machine is assembled. The mast is attached to the key and the key to the base, the main beam is attached to the key and the sides attached to the main beam. The stabilizer connects the two sides near the top, and the hooks allow the sides to be hung from the top of the mast using a cable. Then the rows are added between the sides, and finally the reflectors added to the rows.

The reflectors must be positioned by hand to hit the focal point.