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Re: [VanDeGraaffGenerator] Re: further adventures

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  • Richard R. Linder
    Just for clarification.... I need about 1/4 hp to drive a 5 inch wide belt at about 60 miles per hour. The most practical approach to this was a Variac
    Message 1 of 7 , Jan 1, 2006
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      Just for clarification.... I need about 1/4 hp to drive a 5 inch wide belt at about 60 miles per hour. The most practical approach to this was a Variac controlled universal 1/2 hp motor which measures 4 inches in diameter and 6 inches long. This is all part of my 2nd VDG which is quite large.
       
      Dick
      ----- Original Message -----
      Sent: Saturday, December 31, 2005 10:10 AM
      Subject: [VanDeGraaffGenerator] Re: further adventures

      Oh, I have nothing like 1/2 hp and no need to slow it down. Speed
      control will be by increasing pulley size until motor bogs down.
      Slightly larger motor on order. If you really need a significant
      fraction of a hp to get that kind of current, then I'm probably as far
      along as I'm going to get. Seems like a little more than 1 uA
      available, per my analog meter, and I don't care to risk the other
      one! After what happened to my GFI, I wouldn't use any semiconductor
      stuff without a careful evaluation of the ESD situation!

      I spent too much time yesterday playing with my new toy. Kind of funny
      to launch bits of yarn into the air with it. Have discovered that part
      of the column is slightly conductive, which explains all those
      crackling noises. Can get arcs to a metal probe. May try to replace
      today; time for a trip to the dollar store for another plastic
      pitcher, maybe. That part seems non-conductive so far.
      --- In VanDeGraaffGenerator@yahoogroups.com, "Richard R. Linder"
      <linder@c...> wrote:
      >
      > Lincoln:
      >
      > Don't consider using a solid state speed controller like those sold
      for fan controls etc etc. My VDG uses a 1/2 hp universal motor and I
      tried a heavy duty fan control. First test was with a uA meter and all
      went well. At 50 volts on the motor I managed to get 35uA.  Then I
      disconnected the the meter and installed the HV  terminal.  The first
      arc wrecked the speed control, the motor went to full speed and
      shredded the belt.
      >
      > I am now using a Variac.
      >
      > Dick
      >  




    • Lincoln Ross
      Had an idea for an economical column material the other day: fiberglass driveway markers. Not very expensive, but they seem pretty stiff. I would bundle them
      Message 2 of 7 , Jan 12, 2006
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        Had an idea for an economical column material the other day:
        fiberglass driveway markers. Not very expensive, but they seem pretty
        stiff. I would bundle them up so they more or less resembled the
        corners of the Eiffel tower, except that I'd flare them out just a bit
        at the top, and they'd run together for a ways in the middle so I
        wouldn't have to make any extensive shear structures. I had been
        worried that the radius of the rods (maybe 3 or 4mm??) would be too
        small, but if I'm not mistaken the fiberglass pieces in your second
        VDG have relatively sharp corners.

        Also, I recently rediscovered some carbon tissue in my possession.
        This stuff is remarkably conductive. Just placing my volmeter leads
        against it on opposite ends of a 3 foot roll gives me results in the
        tens of ohms. I may choose to chase the elusive alternative sphere
        material. I've had some experience laying up composites. Now all I
        have to find is an 18" bowl. (I have, someplace, I think, a 13"
        fiberglass hemisphere, but I'm more ambitious. I've moved twice in a
        year so I don't know where all my stuff is anymore.)

        I have an electric motor from a Ryobi weedwacker. I think that ought
        to be sufficient. I like to use a battery to run things so I don't end
        up frying anything in the house. Setting off the GFI several times put
        me on alert. Also managed to fry a compact fluorescent! I'm thinking
        speed control via pulley size will work without having to buy a
        variac. Maybe I'll just roll up tape on the 6mm? motor shaft until the
        belt goes fast enough. Still thinking about cheap sources for the pulleys.

        Do you do any public demos outside of schools? Might be fun to see.

        Lincoln
        --- In VanDeGraaffGenerator@yahoogroups.com, "Richard R. Linder"
        <linder@c...> wrote:
        >
        > Just for clarification.... I need about 1/4 hp to drive a 5 inch
        wide belt at about 60 miles per hour. The most practical approach to
        this was a Variac controlled universal 1/2 hp motor which measures 4
        inches in diameter and 6 inches long. This is all part of my 2nd VDG
        which is quite large.
        >
        > Dick
        snip
      • Richard R. Linder
        Lincoln & all: What started me on the bizarre design of a 4 poster was the fact that an equivalent plexi tube would have required bank loan :-) Each post is
        Message 3 of 7 , Jan 12, 2006
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          Lincoln & all:
           
          What started me on the bizarre design of a "4 poster" was the fact that an equivalent plexi tube would have required bank loan :-)
           
          Each post is composed of two rectangular cross section fiberglass strips 1/4" thick x 4" wide. They are spaced and bolted together at several points to make them rigid. The edges were sanded a bit to "break" the corners but no effort was made to round them over. If I experienced a lot of leakage I would have rounded them over on the table router.  I should not expect any problems with your design especially since you are running a lot lower voltage than my big one.
           
          The weedwacker motor should have plenty of power to do the job. FYI you can slow the motor down with a series resistance like a 200 watt bulb, space heater or some similar type of resistive element. What works depends on th HP rating of the motor.
           
          My demos have been to the schools and also to science major college graduate students who are going for their master's degrees.
           
          Dick
           
        • Lincoln Ross
          I have since recalled saving a fiberglass ski pole, shattered a bit at one end, from the dump. Depending on how much it weighs, it is destined either for a
          Message 4 of 7 , Jan 12, 2006
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            I have since recalled saving a fiberglass ski pole, shattered a bit at
            one end, from the dump. Depending on how much it weighs, it is
            destined either for a model airplane tailboom, or a "one poster". I
            suspect the latter. It's remarkably stiff, although I really have to
            resist the temptation to make it even stiffer by adding carbon fiber
            strips. :-p Not as elegant as the driveway markers, but maybe easier.
            --- In VanDeGraaffGenerator@yahoogroups.com, "Richard R. Linder"
            <linder@c...> wrote:
            >
            > Lincoln & all:
            >
            > What started me on the bizarre design of a "4 poster" was the fact
            that an equivalent plexi tube would have required bank loan :-)
            >
            > Each post is composed of two rectangular cross section fiberglass
            strips 1/4" thick x 4" wide. They are spaced and bolted together at
            several points to make them rigid. The edges were sanded a bit to
            "break" the corners but no effort was made to round them over. If I
            experienced a lot of leakage I would have rounded them over on the
            table router. I should not expect any problems with your design
            especially since you are running a lot lower voltage than my big one.
            >
            > The weedwacker motor should have plenty of power to do the job. FYI
            you can slow the motor down with a series resistance like a 200 watt
            bulb, space heater or some similar type of resistive element. What
            works depends on th HP rating of the motor.
            >
            > My demos have been to the schools and also to science major college
            graduate students who are going for their master's degrees.
            >
            > Dick
            >
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