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lee78

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  • lee78 commented on lee78's instructable Tiny Underground Solar House
    Tiny Underground Solar House

    Here is an earth moving movie (5 minutes)

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  • lee78 commented on lee78's instructable Tiny Underground Solar House
    Tiny Underground Solar House

    Can I still add videos? I'll try with this 1986 arch raising

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  • Electromagnetic Pendulum

    Why doesn't the polarity of the magnet make a difference? As the pendulum approaches the base coil, the increasing magnetic field induces a voltage across the base coil. As the magnet passes over the coil and moves away, the decreasing magnetic field will induce a voltage in the opposite direction. Only one direction will activate the transistor since current won't flow thru the base-emitter junction if the voltage is the wrong direction. So the voltage on the base reaches turn-on threshold either as the pendulum approaches, or as it leaves, depending on the direction of the magnet's poles and the clockwise or counterclockwise winding of the base coil. Once turned on, the battery powered current thru the emitter coil generates a much larger magnetic field and as it increases it induces th…

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    Why doesn't the polarity of the magnet make a difference? As the pendulum approaches the base coil, the increasing magnetic field induces a voltage across the base coil. As the magnet passes over the coil and moves away, the decreasing magnetic field will induce a voltage in the opposite direction. Only one direction will activate the transistor since current won't flow thru the base-emitter junction if the voltage is the wrong direction. So the voltage on the base reaches turn-on threshold either as the pendulum approaches, or as it leaves, depending on the direction of the magnet's poles and the clockwise or counterclockwise winding of the base coil. Once turned on, the battery powered current thru the emitter coil generates a much larger magnetic field and as it increases it induces the reverse voltage in the base coil, turning off the transistor. (I'm disagreeing about the transistor becoming saturated, I think the transformer reverses the voltage on the base coil.) The timing of the pulse thru the emitter coil would be different depending on whether it is triggered by the pendulum approaching or leaving, and that depends on the polarity of the pendulum magnet. ?!

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  • Rotellino - 3€ Battery Free Contactless Bike Light

    I think the core of the coil is ferromagnetic. Why isn't a magnet attracted to the core and stay there?I know eddy currents in the rim generate a field that opposes the movement of the magnet, tending to make the rotor spin. But eddy currents in the coil resist its spinning. Looks to me like the coil is closer, more conductive, and more efficiently configured.

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  • Rotellino - 3€ Battery Free Contactless Bike Light

    I think the eddy current that is by far the largest is the one thru the LEDs, induced in the coil by the changing magnetic flux cutting the coil to generate the emf. There will also be tiny eddy currents induced in the rim (steel or aluminum) like in any conductor near a changing magnetic field. Are those eddy currents in the rim generating enough of a magnetic field to rotate the magnet ring? I don't think so, the magnetic attraction to a steel rim is rotating the magnet ring. (Or is "magnetic attraction" also an Eddy current on the scale of electron spin?)I'm surprised if this works with aluminum rims. Eddy currentEddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction. Eddy …

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    I think the eddy current that is by far the largest is the one thru the LEDs, induced in the coil by the changing magnetic flux cutting the coil to generate the emf. There will also be tiny eddy currents induced in the rim (steel or aluminum) like in any conductor near a changing magnetic field. Are those eddy currents in the rim generating enough of a magnetic field to rotate the magnet ring? I don't think so, the magnetic attraction to a steel rim is rotating the magnet ring. (Or is "magnetic attraction" also an Eddy current on the scale of electron spin?)I'm surprised if this works with aluminum rims. Eddy currentEddy currents are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. -- Wikipedia

    I don't think so. See reply to ajoyraman below.

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  • lee78 commented on DianaHM's instructable Hot Glue Airy Lampshade
    Hot Glue Airy Lampshade

    This is great! I think if it were thread it would collapse in a pile. I have 25 lb fishing line monofilament and I feel, it is stiff on a small scale like 10 mm or a half inch. Your braided line may be even stiffer. Maybe they're about the same thickness -- my old label says .021 I guess that is inches so * 25.4 = .53 mm, you used .55 mm. It takes about an ounce of force to make the monofilament buckle if I grab two places 10 mm apart and try to push them together. That's apparently enough "strut" for such a light structure. I can believe wherever hot glue joints are less than 10 mm apart, fishing line between them will be a strut with enough compression strength to hold the sphere shape. Stiffer line would hold shape with hot glue joints at a greater distance. My guess of 10 …

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    This is great! I think if it were thread it would collapse in a pile. I have 25 lb fishing line monofilament and I feel, it is stiff on a small scale like 10 mm or a half inch. Your braided line may be even stiffer. Maybe they're about the same thickness -- my old label says .021 I guess that is inches so * 25.4 = .53 mm, you used .55 mm. It takes about an ounce of force to make the monofilament buckle if I grab two places 10 mm apart and try to push them together. That's apparently enough "strut" for such a light structure. I can believe wherever hot glue joints are less than 10 mm apart, fishing line between them will be a strut with enough compression strength to hold the sphere shape. Stiffer line would hold shape with hot glue joints at a greater distance. My guess of 10 mm is based on me testing for a minute, and your photos show it works with hot glue drops more like 30 mm apart.I never tried hot glue with fishing line, I'm glad to know it holds. I suppose braided is better than monofilament. A drop of hot glue is MUCH simpler than many designed joints for tensegrity structures. When something deforms the sphere, the strength of the lines in tension and of the glue mean that the tensile network will not break, the deformation will happen only as the compression struts buckle. And fishing line is so resilient when it is bent, it pops back to sphere shape as soon as the deformer is removed, right? Maybe you have to do a little patting to push out big dents. I think your construction would hold ANY shape if you started with a mold other than the balloon. (and used many joints on tight curves so lines are straight.)

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  • lee78 commented on DianaHM's instructable Hot Glue Airy Lampshade
    Hot Glue Airy Lampshade

    I'm impressed! Designers of geodesic domes and tensegrity structures think hard about optimum strut and cable lengths and orientation. Maybe you've shown me a new tensegrity design principle -- if you have enough joints, the orientations and lengths can be random!

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  • lee78 commented on DianaHM's instructable Hot Glue Airy Lampshade
    Hot Glue Airy Lampshade

    I'm surprised it holds its shape! I haven't tried this so I'm glad you did -- I expected it to droop into a cylinder or pear shape if it were hanging from the plastic circle. Or flatten on the bottom resting on a table. But it stays spherical ?! How thick is that fishing line? I think the glue is mainly at crossings, not spread along the fishing line (that would make it stiffer).

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  • lee78's entry Tiny Underground Solar House is a winner in the Tiny Home Contest contest
  • lee78's entry Tiny Underground Solar House is a finalist in the Tiny Home Contest contest
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  • lee78 commented on lee78's instructable Tiny Underground Solar House

    raccoon on table looking in door didn't see meI wasn't inside when bear cub saw reflection in door (right edge of photo) and ran off

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  • lee78 commented on lee78's instructable Tiny Underground Solar House

    The house design would need a longer overhang over the south windows or another way to shade them during summer given the lower sun angle in Alaska. Or maybe the floor would absorb more summer heat that you would get back in winter. Here deciduous trees provide summer shade and lose their leaves to allow sunlight to the windows in winter. The lowest outside temp I've seen is 3 F, (inside 44 F.) There may be a week or 10 days when it does not get above freezing outside.Owner-builder smugness compensates for snugness. Also, an air temp of 50 F is much more comfortable in here than in a poorly heated above ground house; I think radiant heat from the thermal mass of earth all around is more important for comfort than air temp.An electric blanket is the only heating equipment I routinely use…

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    The house design would need a longer overhang over the south windows or another way to shade them during summer given the lower sun angle in Alaska. Or maybe the floor would absorb more summer heat that you would get back in winter. Here deciduous trees provide summer shade and lose their leaves to allow sunlight to the windows in winter. The lowest outside temp I've seen is 3 F, (inside 44 F.) There may be a week or 10 days when it does not get above freezing outside.Owner-builder smugness compensates for snugness. Also, an air temp of 50 F is much more comfortable in here than in a poorly heated above ground house; I think radiant heat from the thermal mass of earth all around is more important for comfort than air temp.An electric blanket is the only heating equipment I routinely use, but dehumidifier, water heater, my 1982 refrigerator, a couple of incandescent light bulbs etc contribute their electric load in the form of waste heat. The power has not failed in recent winters, so I could use a portable 1750 watt electric heater, but I don't. I also don't use a portable kerosene heater except to test it. A carbon monoxide detector assures me there are enough leaks in the window walls so ventilation is not a problem. (Who thought to seal the cracks between the planks near the ends?) My sister sent a big BULKY sweater and a thermal blanket she designed and crocheted. The blanket has a section at chest level with an overlapping layer formed into two wide arm holes, so I can stick my hands thru to operate a keyboard without pulling the blanket below my shoulders. A wool ribbon 3 inches wide and 4 feet long is sewed to the top of the blanket at the ribbon's middle. I wrap the two ends of the ribbon around my neck, like a scarf. It keeps the blanket from slipping down when I sit up.

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  • lee78 commented on lee78's instructable Tiny Underground Solar House

    On a moonless night if I don't leave a light on inside that is a problem even when I know the door is nearby.

    I like!

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  • No, the heat used to vaporize water is wasted if your purpose is to raise the air temperature. While the heat from burning wood is raising the water temperature from room temp to boiling, that heat in the water IS added to the room and not waste BUT when the water reaches boiling temperature it stops rising in temperature. Lots of heat then goes to vaporizing the water at the boiling temperature. So the room gets humid with steam, but the heat used for vaporization would have gone in to heating air to a higher temp if the wood had been drier. Wet wood wastes heat because so much of the heat does not warm air or water, it just converts water to steam at constant temperature.

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  • lee78 commented on anil8tor's instructable Solar Heater for My Shop

    This 12' C-band satellite dish provided domestic hot water in 1983 and collected TV with a cassegrain feed. Sunlight was absorbed at collector, microwaves bounced off to LNB on dish surface.. I wrote the program for the VIC-20 (lower right) that computed the position of the sun every 5 minutes and adusted azimuth and elevation motors.

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