Slip Rings and Domed Observatory -- Continuing

Discussion in 'Misc Electronics' started by W. eWatson, Mar 24, 2013.

  1. W. eWatson

    W. eWatson Guest

    Well, things are really starting to move with my attempt to put a
    control system in my 10.5' dia dome. There's no doubt,finally, this is
    going to happen in the next few months. The control system will allow me
    to move the shutter and rotate the dome via my PC to allow my telescope
    to point to the open sky where I want to say photograph something. There
    are two 1/2 HP motors. One controls the shutter position, and the other
    the rotation.

    Before the installation occurs, some weeks from now, I would like to
    know what the better understand the slip ring mechanism is that is
    likely useful in this installation. It supposedly provides continuous
    power and would be located around the skirt of the obs. The skirt is the
    wall area below the dome. I think it consists of three copper tubes that
    follow the perimeter of the skirt.

    It's easy to see how it would provide power for the rotation motor,
    since it is attached to the top of the skirt and its gear meshes into a
    track along the bottom of the dome. However, what I don't get is how it
    can provide power to the shutter motor at the top of the dome.

    Presently, a power cord comes from the skirt up to it, which at times
    can wrap itself around the telescope. That has to be eliminated. It
    makes no sense that a cable would come from the ring to it. My guess is
    that there must be wire brushes that somehow connect power to the
    shutter motor between the ring and the shutter motor. Can someone square
    me in how this really works? BTW, would putting the ring mechanism in
    require replacing my 110v motors with 220v motors?
     
    W. eWatson, Mar 24, 2013
    #1
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  2. W. eWatson

    Jamie Guest

    I am trying to envision why this would be a problem?

    In any case, you can have multiple slip rings to get around obstacles
    like gears and bearings on the mass the rings maybe mounted to. The idea
    is to put a channel (slot) under the gear/bearings and pass the wires
    under to the upper set of rings. from there, you can extra power with
    out any problems? Another set of brushes are then used.

    But still, I thought the whole obs turns on the post and why should the
    shutter not be turning with it? In which case, the slip rings on the
    skirt as you say, will be stationary and the brush assemblies will be
    mounted on the base of the obs that turns.

    Jamie
     
    Jamie, Mar 24, 2013
    #2
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  3. W. eWatson

    W. eWatson Guest

    Nor do I. It came up in a talk with the installer, but was probably
    unrelated to slip rings. I'll stick with 110.
    I'll leave these details to the installer.
    Ah, so brushes are involved. I have no idea how this would be done to
    cross from the skirt to the dome. This comes close to showing them and
    the rings in a professional obs.
    <http://www.astronomical.com/products/dome-control>. See the photo on
    the right about 1/2 way down. One can see the rings under the shelf. I
    don't see any brushes.

    This shows a use of rings in a photo a little big dowt on the right.
    Those are big brushes! See the legend under the photo.
    Presumably the power would go to a control box on the side of the done
    for the shutter electronics (circuit board, relays, limit switches,
    motor), and another like it on the skirt for rotation. Gnomes are not
    allowed, but I've had a bird or two try to get through the open shutter.
     
    W. eWatson, Mar 24, 2013
    #3
  4. W. eWatson

    W. eWatson Guest

    The of the obs as a silo. There is no post. The dome rolls on a track
    sitting on the skirt driven by a motor.
     
    W. eWatson, Mar 24, 2013
    #4
  5. W. eWatson

    Jamie Guest

    Sounds like an easy job then.

    I've seen induction power coupling that works very nice for that, it's
    nothing more than a transformer primary at the fixed base and the
    rotating part has the secondary of the transformer sitting inside the
    primary section. There are no slip rings and things are done wireless
    from a remote point.

    Jamie
     
    Jamie, Mar 25, 2013
    #5
  6. W. eWatson

    Don Bruder Guest

    Overkill much?

    There's an old saying - an elephant is a mouse built to a committee's
    specifications. Your idea is a prime case of that. You're trying to
    "over-tech" it beyond ridiculous for no significant gain. I suppose
    you'd advocate using a sledgehammer to swat a mosquito that just landed
    on your forehead, too?

    A simple, reliable, purely mechanical solution in the form of slip rings
    and brushes will do the job more than adequately, be ultra-low
    maintenance, cost *A LOT* less, both to install and to operate, be
    orders of magnitude lighter, will be reasonably weatherproof without the
    need for expensive enclosures, won't generate anywhere near the amount
    of heat (which equals lower operating cost due to not having the waste
    of electricity being turned into heat instead of motion) that a magnetic
    coupling would, and have too many other benefits compared to inductive
    coupling for me to even try listing them all here - the ones I already
    listed practically wrote themselves - if I were to actually sit down and
    ponder the idea, I'd probably come up with dozens more.
     
    Don Bruder, Mar 25, 2013
    #6
  7. W. eWatson

    Don Bruder Guest

    My best guess from the picture is that the brushes are hidden by the
    motor.
    And now I think I know where the 220 versus 110 question comes up - The
    page you're looking at *SEEMS* to be written specifically for a 220
    (240, actually, but lets not quibble) volt system. Exactly the same
    concepts apply for both voltages - You've got 3 rings on the tower, each
    isolated from everything else, and all 3 stationary. For a 110 system,
    one rai gets connected to "hot" (110 volts relative to "ground"), one to
    "neutral" (theoretically zero volts relative to ground, in practice, not
    ALWAYS true), and the third to "ground" (which, for 110, is the
    so-called "safety ground") For a 220 system, instead of "hot, neutral,
    ground", the labeling is usually "L1, L2 and ground" (Each of "L1" and
    "L2" are +110 volts relative to "ground", giving you a total working
    voltage of 220 volts)

    On the dome side, you've got three brushes - each one will be a piece of
    spring metal (perhaps something like a strip of phosphor bronze)
    pressing a block of graphite down against one of the three rails. for a
    110 system, one brush will be riding on the "hot" rail, another on the
    "neutral" rail, and the third on the "ground" rail. Same thing for a 220
    system, but the brushes are called "L1", "L2", and "ground" respectively.

    Put it all together, and the whole mess gets power - either 110 or 220 -
    across the gap between the tower and the dome, with no solid wires
    connecting the two pieces, leaving the dome able to rotate freely. A
    wire from each brush then goes to a junction box mounted on the dome,
    where anything on the dome that needs power can be connected - Notice I
    said *ANYTHING* - the rotation motor, the shutter motor, electronics to
    control both, a fluorescent light fixture, a socket to plug in a
    blow-dryer to unfog the 'scope mirror - ANYTHING you can imagine that
    might need to both have power, and rotate with the dome can be powered
    out of that junction box. (up to the limits of the wiring supplying the
    juice, of course - if you've only got a 50 amp circuit powering it, it
    should be obvious that you're not going to be able to run 100 amps worth
    of gear)
    Yep, exactly.
     
    Don Bruder, Mar 25, 2013
    #7
  8. W. eWatson

    John Nagle Guest

    It's not clear what you have, what you're buying, and what you're
    building.


    John Nagle
     
    John Nagle, Mar 25, 2013
    #8
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