• Mechanics 24.09.2008 No Comments
    CNC with notchplate

    CNC with notchplate

    Another part for the CNC router arrived today. I never expected it to be delivered so fast. I ordered it friday afternoon and payed saturday. I was not at home when the package arrived, but fortunately the DPD employee decided to give it to my neighbours instead of taking it back with him. Might have something to do with the weight of the package (ca. 9kg) ….

    And another order arrived today: 136 neodymium magnet spheres of 5mm diameter. They are so much fun to play with and even have educational value! You can visualise some basic materialsciences principles such as close-packing of spheres and edge dislocations.

    Even platonic solids can be constructed. Unfortunately I only have enough spheres for two pentagonal dodecahedrons (made of twelve pentagonal faces) and one decagonal dodecahedron made of twelve decagonal faces.

    Decagonal Dodecaeder

    Decagonal Dodecahedrons

    Pentagonal Dodecaeders

    Pentagonal Dodecahedrons

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  • Eddy Current Video

    Eddy Current Video

    Take some strong neodymium magnets and place them onto a nonmagnetic but conducting material (for example aluminium). Then tilt the material and let the magnets slide down.

    You will notice that the magnets slide down slower than expected. This is due to the eddy currents which are induced in the conductor by the moving magnetic field of the magnets. The currents themselves generate a magnetic field with opposite polarity. The two fields attract each other therefore slowing the magnets down.

    This a nice demonstration of Lenz’s Law where the generated field counteracts its generation.

    Another cool demonstration of the effect can be found here.

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  • Christmas Lights reused

    Top view

    When clearing out the basement a found an old chain of lights for christmas decoration. Many bulbs were burned out but a litte box at the end looked worth opening, as the lights could blink in different patterns. Inside the biox was an IC and four transistors for driving the lamps.

    Christmas Lights reused

    Bottom view

    I plugged it in and measured the signals at the pins of the IC and discovered, that the chip was clocked by the mains frequency but needed no other signals except a button for switching the pattern.

    I decided to replace the lamps by leds and place everything on a small circuitboard.
    At every channel of the IC there are four blue leds. All sixteen leds are placed in a circle around the other parts.
    The clock is generated by a good old NE555 timer.

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  • While the mechanics are nearly complete, the wiring has just started.

    CNC Wiring (Z-Axis)

    CNC Wiring (Z-Axis)

    The light barriers are now all mounted but the metal sheets to trigger them need to be cut and attached.

    CNC Cabling (Z-Axis)

    CNC Cabling (Z-Axis)

    To shield the cableconnections from metal filings and such i placed a small plastic housing at the Y and X axis near the motor. All cables go into those housings through sealed holes. Inside they are connected by luster terminals.

    There will be 3 cables going to the z-axis. One for the motor, one for the 220V socket and one for lightbarriers and 12V supply. These cables are guided by a cable drag chain to prevent tangling.

    Next thing to do after the cabling is complete is to order the notch-plate and etch the interface boards.

    The coupling-problems are nearly solved. The 12mm holes for the motorshafts were misaligned, but the new holes look good. Maybe the holes in the frame for the couplings to go trough need some filing.

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  • Parallel-to-I²C-Adapter


    Just a little circuitboard to interface I²C-chips to the parallel-port.

    I designed the layout so it can fit inside the case of the connector.

    An additional diode to protect LS05 from reverse polarity might be good. (I already ‘converted’ one to smoke 🙁 )

    Eagle5 layout and some simple TurboC++-Code for the adapter can be downloaded here.

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  • Chemistry 11.09.2008 No Comments

    I don’t know what my motivation for this experiment was, but the outcome was surprisingly successful.

    Normally sodium is produced by electrolysis of an eutectic mixture of sodium chloride and calcium chloride, but this requires high temperatures of about 700°C.

    Sodium production 1. try

    Sodium production 1. try

    So I went for the so-called Castner process, which is based on electrolysis of molten sodium hydroxide. This requires only a temperature of about 330°C, which is easily achievable by an alcohol burner.

    To protect my table from spills of molten sodium hydroxide, I placed the bowl that contained the melt inside a metal can. To guarantee heat conduction and electrical contact i placed the bowl on top of some tin, which would then melt and provide good connection between the two cans.

    The cathode was a thick steel wire which was placed above the can.

    The first try was moderately successful. As you can see in the photos, a lot of blue crystals formed. I don’t know where they came from and they did not occur in the second try.

    Sodium production 2. try

    Sodium production 2. try

    A small droplet of molten sodium quickly formed at the cathode but it proved to be nearly impossible to get it out of the melt. I finally manged to get some out with a loop of wire. The sodium was immedatly put in molten wax to protect it from humidity.

    Next time i will try to build something resembling the draft from the wikipedia article to get better results.

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  • Solving stuff in other stuff can be exhausting. I first discovered this problem when making the PVA slime. The pva-flakes did not dissolve completely when stirred by hand. So i looked up magnetic stirrers on eBay and immediately decided to go for plan B: build one myself.

    Magnetic stirrer

    Magnetic stirrer

    I previously had bought some strong neodymium magnets and just needed something rotating to attach them to. The first thing i found was an old 8cm fan. I had concerns on wether the magnets would interfere with normal motor operation, but they proved to be needless.

    To magnets were glued on top of the rotor with opposite poles facing upwards. I used double-sided adhesive tape and superglue and another layer of tape on top.

    For the stirrer itself i used a small cylindrical magnet. To protect it from aggressive solutions i stuck it in PVC tube and sealed the ends by melting the pvc.

    Then i tested wich distance from the rotor was best to achieve good rotation of the stirrer and place a piece of plexiglass over the rotor in that height. (Fortunately i had screws that fit perfectly).

    As you can see in the picture, it worked quite well.

    If you want heating too, you can just place a peltier-element between the stirrer and jar.

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  • Chemistry 09.09.2008 No Comments

    In my entry about the slime I mentioned fluorescein as dye. Today I am going to explain how I made it.

    I had some phthalic anhydride and resocinol in an old chemistry set but the resorcinol was quite dirty so I got some new at the pharmacy.

    Most synthesis instructions recommend zincchloride as catalyst but some drops of sulfuric acid work as well. (Sulfuric acid and zincchloride are both hydrophile, which is the needed effect).

    Fluorescein drop in water

    Fluorescein drop in water

    15g phtalic anhydride an 22g resorcinol are ground to a fine powder and placed in a test-tube and heated. I used an alcohol burner but i recommend a hot air gun.

    When the powder melts and turns into a thick, red, honeylike substance stop heating and let it cool down.

    The fluorescein can then be dissolved in a small amount of water resulting in a dark red/brown solution.

    One-two drops of this solution are enough to colour 500ml of water to a bright green.

    The best results are achieved when the coloured water is viewed in sunlight.

    A more detailed synthesis manual can be found at LambdaSyn.

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  • Chemistry 08.09.2008 No Comments

    Polymers are always fun. Especially when they are slimy.

    A great polymer gel can be made from Polyvinylalcohol and Borax (Disodium tetraborate).

    Just prepare a 4% solution of Polyvinylalcohol (i used the one with a molecular weight of 72000) and a 4% solution of disodium tetraborate.

    The PVA best dissolves under constant agitation and slight heating. Let it stir until the solution is clear and has no chunks left in it.

    Then add 2 parts of the boraxsolution to 10 parts PVA-solution and stir until the consistency gets slimy.

    PVA Slime coloured with fluorescein

    PVA Slime coloured with fluorescein

    If you want to color the slime, add the color to the PVA prior to adding the borax. A few drops of fluoresceinsolution give it a nice, shining green and quite some resemblance to Flubber.

    The slime quickly dries out when stored open, so it is best keept in a glas jar or in a plastic bag. This also delays the growth of mould in/on the slime.

    I have not yet tested the effect of preservative agents on the moldering.

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  • Chemistry 08.09.2008 No Comments

    Always fascinated with the look of liquid metal but not keen on burns from molten tin, i bought about 20grams of Gallium from eBay.
    Unfortunately it came in a glass vial, which is bad, because Gallium readily wets glass. So quite a bit stayed inside attached to the walls. The rest was liquid although it had a temperature below its meltingpoint of 302.9K (29.7°C). This was due to its tendency to supercool.

    The drop had an unattractive oxide layer on top which was removed by sucking the gallium out with a plastic syringe.

    Then some drops were placed on the cool side of a peltier element to solidify them.

    Gallium drops

    Gallium drops

    After discovering a recipe for an alloy that stays liquid down to -19°C that required Indium, i bought 8grams of Indium form eBay and mixed a small amount of the alloy.

    Only 1.44 grams of Galinstan were made, because i did not want to ‘waste’ so much Gallium and Indium.

    Details on the weight ratio can be found in US Patent #5508003.

    Gallium and Indium are important resources, mainly in the production of leds.  Those resources are getting rare. (For all germanspeakers: Interesting report on resources)

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