• 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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  • 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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