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Demotech News

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News Mon Mar 17 (2003) -- Thu May 22 (2003)
News Wed Dec 04 (2002) -- Mon Mar 17 (2003)

Design, hands on

Thu Nov 28 (2002)

I tried hard, but could not work out a work out in advance a proper set-up for the core of the stove, the firebox that should fulfill the following demands:

  • The channels in the stove had to fit inside the two walls erected last week.
  • Parts for firebox and channels should be stacked on top of- or next to each other and stay in place without plaster.
  • Parts should take compression loads only and no bending force, specially when in contact with intense heat. When cracks occur over time, this will prevent displacements of parts.
    Today I let the actual situation be my guide. Together with Hans and Zuhair we took only the step that was evidently appropriate, before considering the next.

    Zuhair removed top and bottom of a 200 liter oil drum and cut open and flattened the side. From this sheet metal he shaped the duct, that will be fastened between the top and bottom concrete slabs, outside of the wall. (see picture)
    I regretted not to have available an ax or cutlass. Zuhair had to work with good quality tools such as an electrical hand fret saw and a table sheet cutter to cut the sheetmetal parts.
    From experience I know that the seemingly more prmitive working with an ax for cutting and a dull cutlass for folding works by far faster and more accurate. Just an underground of dirt works best. I still have to describe these methods in this website.

    Hans and myself worked on composing the setup for channels and fire box inside the brick walls.
    - Directly over the concrete slabs a metal sheet rest on strips of bricks to facilitate heat exchange between the cold inlet air and the hot gas from the fire box.
    - The firebox is wide at the top and narrow at the bottom. This is done by placing two tiles slanted against the outside walls. The space behind the slanted tiles functions as the channel to guide preheated air to the opposite side, where this air can enter between the grates of the fire box.
    - As grates of the fire box function four tiles placed between the two slanted outward tiles. The proper distance between the tiles came from placing small stone wedges between the tiles. (see picture)

    We expect it to function as follows: Fuel wood slides down from the container to the top of the grates, that is the top edge of the tiles. Burning parts falling off, slide down while burning to a smaller size. Small parts falling through, burn to ashes on a plate positioned under the fire box.
    - Hot gas from the fire box moves horizontal through a channel, then up to a channel on top of the first. Then is can escape side ways into the meal ducts as Zuhair has been working on. From there flows out to the chimney (shown near the window).

    Hans indicates with the empty container for wood fuel where it will later be positioned (see picture)
    Building blocks with a special shape as used this time will later be cast from concrete or heat resistant cement. For this experiment Hans cut them to size with a fast running diamond disk, a very dusty job.

    To design hands on, with clear preset conditions but without detailed plans, works well to overcome a deadlock in design. As the problems are clearly visible for all involved, ideas come in at the right time. This was how it went during most of this job. Only at the very beginning misunderstanding and distrust in the good outcome hampered effective cooperation.

    Frame for pulley wheel

    Sat Nov 16 (2002)

    A safety pin inspired the shape and function of the frame for the pulley. We choose 5 mm concrete reinforcement rod with a ribbon (rebar). This rebar is a springy kind or steel, with an undulated surface (to increase grip when cast in concrete). Available in most places as new material or as reclaimed from demolished buildings.
    The frame can be opened near the top to attach the hook of the frame to a support and/or to put a hoisting line over the wheel.
    At the vertical parts are metal strips attached, to which the axle (-pins) of the pulley wheel are tied with rope. This unconventional method may prove helpfull to achieve low friction, easy repair, no need for lubrication and therefore no chance of spoiling water.
    Next step will be a guide to assure that the rope always runs properly in the middle and can not get stuck besides the wheel.

    Work on the Travel Bed in preparation for Senegal

    Fri Nov 15 (2002)

    When traveling in Senegal it would be nice to use the Travel bed. The idea is to have a cabin luggage size suitcase, that can be split up in two equal halves. Put next to each other, these box-like units act as a base for a framework that carries a tensioned netting on which one can sleep. Netting and frame parts take only a small portion of the space in suitcase during transport and weight but little.
    Today Paula and I made a test on a new setup to accomplish the above target. Vertical sides of cloth tension up the cloth or netting that has to carry the weight of the user. Our finding was that the tension was not the problem, but the side way stability of these tensioning cloth parts. Plasitisized cloth may perform better.
    Putting a heavy sand bag on the test contraption raised hope, that indeed a construction out of these light sticks will do the job.

    Masoning a woodstove out of bricks

    Wed Nov 13 (2002)

    Today we started bricklaying for the wood stove in the workshop of Hans Baarslag and his colleagues Johan and Zuhair. On a frame, welded out of steel tubes, four concrete pavement tiles (size 60 cm x 40 cm) are placed. Five layers of bricks form a wall. On the inside horizontal channels will guide the hot air from the actual fire hearth to the outside of the wall.
    Metal sheet panels placed outside this wall further guide the smoke to the chimney, while transferring its heat to the workshop. The picture shows the way in which the roofs of the channels are made out of two bricks resting against each other.
    We used mortar made out of 1 part dry sand mixed with 1 part powdered clay. When dry, this is easy to mix, then water is added. We will experiment with a mixture of 1 part powdered clay with two parts dry sand. A 1 to 1 mixture is rather soft and limits the number of layers that can be laid to three to prevent sagging.

    More light out of less batteries

    Tue Nov 12 (2002)

    In Western economies a breakthrough is expected in the development of ever more effective Light Emitting Diodes. These components develop with the speed similar to computers: Fast improvement of functionality and steep reduction of cost in a short time.
    In the circuits of the NightReader as developed and used up to now the LEDs are not the limiting factor regarding cost. Now it is the cost of generating electricity. With the NightReader working on near empty discarted batteries, Demotech could make a sort cut through this problem.
    However we should prevent any loss of tension or current in the circuits used. Today Jos Knoop told me he found the right components to reduce the tension almost by half, as needed from the batteries to let the LEDs function. This means enormous progress for practical use. The chance to find four still useful batteries is far greater then the six to eight batteries as needed now.
    I established a contact today among Jos Knoop and Jos Spanbroek of "De Spelerij". Jos Spanbroek has an interest in playfully used LEDs powered bij solar cells. He expects he can arouse a lively interest in the mind of young people if they find out how these LEDs function and how usefull they are. Jos Knoop will prepare a setup for demonstrating what can be dome in this field.
    I am very happy with this cooperation, as I can learn a lot of the possibilities of a more general use of LEDs for illumination.

    Senegal instead of Bangui

    Sat Nov 09 (2002)

    Willem is safely back from Bangui. He traveled with a group expats from Bangui to Cameroon and flew home from there. I do not expect the situation in Bagui to be stable soon and am forced to cancel the plan to go there. Instead I will visit Senegal for three weeks.
    My plans for Bangui centered on the NightReader. In Senegal the issue is water lifting, with pulley and rope pump. I will accompany Ives Faye to his Keur Massou farm project. I expect to have plenty of chance to try the NightReader as well. Specially after sunset!

    Wood burning stove build from stones

    Sat Nov 09 (2002)

    Together with Hans Baarslag and his two compagnions Johan and Zuhair, we made the first setup of the new design for a stove as described in the list . We experimented in Hans new workshop, a former cow shed with no heating.
    This is what we are heading for:
  • The stove will have a table like model. It rest on a metal frame 30 cm above the ground and is about 1 meter high.
  • The stove is constructed out of concrete paving stones (60x40x6cm) for bottom and top. In between bottom and top two walls are masoned from ordinary bricks with mortar. This mortar is just a 1:1 mix from clay and sand. Fire-resistant concrete tiles for lining are only used where the wood is burning.
  • Air is pre-heated before ist reaches the fire. To attain a very high burning temperature the actual fire place is small. It is expected the fuel will be consumed at a slow pace. This is in contrast with nomal wood burning stone stove that burn their fuel fast.
  • The hot air on its way to the chimney is guided outside af the brick walls, behind metal sheets, that clamp inbetween the top and bottom. These metal sheets can be cut from a flattened oildrum.
  • Wood as fuel is fed into the fire from a pipe-like container positioned above the fire..The container is closed at the top

    Bangui in trouble

    Sun Oct 27 (2002)

    Last contact with Willem van Tijen by telephone was on Friday. Willem reported hearing explosions. I expect him and the people from Medicins Sans Frontieres able to manage their present situation. The chance to go to Bangui next month is small. Possibly I should divert the intended work to a location in Senegal.

    From Bangui to Senegal and back

    Fri Oct 25 (2002)

    I plan to go to Bangui from the 15th of December for a month stay. My Senegalese friend Ives Faye asks me if I could make a return trip from Bangui to Dakar to prepare for the irrigation of his Keur Moussa farm project. Looking at the globe I discover these two towns are not that far apart comparing to the distance from Holland. He tells me the climate is fine around Christmas, cool, no mosquitos!
    Today we practised cutting a ring out from a car tire. Cutting rubber is easy if only you use a sharp knive and force the sides of the cut into the rubber apart. If this is done well, rubber cuts like butter. But it takes practice to do it well.

    Step 1 is making a knive out of a broken hacksaw blade. Sharpen the tip and wind a strip of inner tire around the rest of the blade as a handle.

    Step 2 is pushing sticks inside the car tire that spread the flanges as much as they allow.

    Step 3 is making a circular cut at the right place for the pulley. A circular line indicates where the side of the car tire fits against the flange of the steel wheel. The right place for the cut is just the width of a saw blade away from this mark.

    Step 4 is dividing the ring into two equal halves. Measuring is done with a straight stick and a straw.

    Step 5 is cutting the rings loose from the rest of the tire. Be aware very little force was needed. While one's hand is cutting one way, make sure your other hand is safely doing something helpful in the other direction.
    Never your fingers should be in front of the knive.


    Newest model NightReader now in Bangui/CAR

    Mon Oct 21 (2002)

    Willem, since yesterdy again in Bangui for aircraft maintenance took with him from here six NightReaders. I want more people to get user experience, also an expectation that this little device should become more widely available. The first user comments will come back in one or two weeks. I am ready to give follow up to that with improving on the present design.
    The present latest model uses only one LED, using 10 mA, 2.5 V because it emits yellow light. the diffusion angle, meaning the width of the ligt beam is wide, 70 degrees. The cost about 20 Euro cents if bought in some quantity.
    These NightReaders are constructed as if done with local aids, apart from the electronic components: wood for the handle, roof sheet for the shade wiring from a scrapped car. The little pincer made out of a bicycle wheel spoke proves to be very usefull for making the tiny holes.
    Keeping components on one side of the thin wooden circuit board and soldering on the opposite site works well. Cross over interconnections are made by bit of insolated wiring placed over the electronic parts. I look for smarter circuits. Jos Knoop researches on a more appropriate tyristor, Marc came up with a source for relevant info at the website "Circuits on Line"(see forum page NightReader). I will do some testing myself to get an idea how long the NightREader takes to drain the energy out of used batteries with a to low voltage for practical use.

    News Fri Oct 11 (2002) -- Tue Aug 27 (2002)
    News Tue Aug 27 (2002) -- Mon Jul 01 (2002)