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Falling leaves problem

Discussion in 'Electronic Basics' started by Niklas Borson, Apr 23, 2004.

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  1. I'm an raw beginner in electronics, and would like some feedback
    on an idea before I take it any further. I will first describe
    the problem and then my proposed solution. My question is whether
    the solution makes sense. Any other advice would also be welcome.


    The basic goal is to hold onto something for a period of time
    and then drop it. It must be possible to reattach the object
    and do this again, over and over. The time might be anywhere
    from a few seconds to several hours or more, and should be
    adjustable, but accurate timing is not required. In fact, a
    degree of randomness would be a nice effect. The object to be
    held is light -- less than an ounce. Simplicity, low cost, and
    low power consumption are goals.

    It may help to know the actual application. My father is a
    sculptor, and has been toying for some time with an idea, part
    of which involves a tree gradually shedding its leaves.


    My idea is to hold the leaves on magnetically. Each leaf would
    have a metal stem, which would attach to an inductor on the tree.
    From my reading, I gather that if an inductor's core is made of
    something like ferrite, the core will remain magnetized even
    after the curcuit is opened. Here then is the process I have
    in mind:

    1. Charge the magnets. The user would close a switch for some
    period of time. Each inductor would be on a different parallel
    circuit with a unique resistance so as to magnetize some
    cores more than others.

    2. Stop charging and attach the leaves (not necessarily in that
    order). Once the circuit is opened, the leaves are held on
    by the megnetized inductor cores.

    3. Wait for cores to gradually become demagnetized, such that
    the leaves fall off. This should happen unevenly since some
    cores were more magnetized that others.

    The above makes a lot of assumptions that I don't know to be
    true, e.g., that the inductor cores can be magnetized in a
    reasonable amount of time, and will gradually demagnetize once
    the current is turned off.

    What I like about it, though, is its simplicity -- no digital timers
    or complicated logic circuits. My father had an idea of attaching
    the leaves with wax and then gradually melting the wax. The above
    approach is in intended in the same spirit, only easier and less
    messy. The only problem is... I have no idea whether it would
    actually work.

    Thanks in advance for any advice.

  2. Nick,

    I don't think you need ferrites for this purpose. On the contrary, ferrites
    are roughly divided in hard - and soft ones. The first keeping their
    remanent magnetism for a long time and the second loosing it almost
    instantly. Guess the best core material you can use is simple iron like the
    material used for ordinary nails. But even then you will have to do some of
    experiments to find the relation for type and dimensions of core material,
    number of turns of your coils, current, time to magnetise, weight and type
    of the leaves and so on. I'd use paper or plastic leaves with a staple for
    the magnetic tag.

  3. Gordon Youd

    Gordon Youd Guest

    Why not make the magnets all the same, the leaves can be attached while the
    power is "on", when power goes "off" leaves fall to ground.
    Now the nice part, you can get glues and such that gradually unstick. Hey
    presto! leaves would unstick quite randomly..........

    Regards, Gordon.

  4. This sounds like an interesting idea. Can these guess stick, unstick, and
    restick over and over? I would think they'd kind of lose their stick after
    a while, although I suppose you could just apply more glue then.

    Do you know where I can look for this kind of thing? I've found the local
    Radio Shack to be pretty useless, and haven't had much luck with online
    catalogs either, mostly because I guess I don't know exactly what I need.
    (I guess no store can really help me in that case...)
  5. Huh, this sounds like the kind of laborious experimentation I was hoping
    to avoid. Just lazy I guess. I did try wrapping some magnet wire around a
    small nail and hooking it up to an ordinary 9V battery. It functioned as
    an electromagnet while the circuit was closed, but the nail itself never
    became magnetized. Maybe it was the wrong kind of material -- it was just
    a little wire nail like you use to hang pictures with.

    Another option I had toyed with was holding the leaves on with ordinary
    magnets. Each leaf would have a magnet at the base of its stem so it could
    hang on any piece of metal -- the tree, the refrigerator, whatever. The
    anchor point on the tree would have a coil around it. As long as there
    was no current, the leaf would attach to the metal core of the coil. But
    if I sent a pulse of current through the coil it would create another magnet
    with the poles aligned in such a way that they repelled each other. That
    was the theory, but I couldn't make it work. Also, this design requires
    some means of sending pseudo-random pulses of current to individual coils
    which sounds complicated to me.

    Thanks for the help. I think I need to look around some more for an
    approach that's more within my abilities (and time), possibly something
    non-electronic. Gordon's glue suggestion was interesting.
  6. Seth Koster

    Seth Koster Guest

    Huh, this sounds like the kind of laborious experimentation I was hoping
    You could try putting various values of caps in the circuit, each
    one discharging through one of your electro-mags, so when you turn off
    the current each cap discharges and drops the leaves in a 'random
    looking' pattern, depending on the value of each cap.
    I have no idea if this would work since this is very far from
    anything I've ever tried to do (or even thought of trying to do), so
    I'd appreciate a post from anyone who could debunk or verify this
    possibility. Maybe coils of different inductance for each node? A
  7. Gordon Youd

    Gordon Youd Guest

    The idea I gave using "glues" was just to show a different way of doing what
    you want.

    The other way would be to take a couple of metres of thin wire and starting
    at one wind a small coil of about 10-20 turns around a paper clip.

    Take out the clip, move on a few inches and wind another coil.

    Do this again until the wire is used up.

    You will end up with a long strip of coils,.

    Make paper leaves and fix a small piece of paper clip to each leaf.

    Connect each end of the wire to a battery 3-6 volt, you may have to put a
    resistor or bulb in series to prevent too much current.

    With the battery connected you will find there is just enough magnetic flux
    at each coil to hold a leaf.

    If you had about six of these coil strips made you could distribute them all
    over the tree like a set of christmas tree lights.

    Cutting off power using a timer to each coil strip would only drop those

    If you made some variation in coil turns and using a variable resistor,
    turning the resistor down would make each leaf or two drop off because the
    current is unable to hold them on.

    Play about with the paper clips on each leaf would make them weigh

    Hope this helps.

    Regards, Gordon.
  8. Take out the clip? Don't I need something in the middle, if
    nothing else to physically hold the wire in place?
    Cool. I like the idea of having multiple leaves per circuit
    because it seems like it would reduce the number of components.
    Having the leaves fall in distinct groups doesn't sound
    random-looking enough.
    This sounds better. The leaves would fall "randomly" when the current
    dropped below a threshold, which would depend on several factors: the
    inductor, the weight of the individual leaf, and perhaps even forces
    on the leaf due to air movement.

    It seems like I should only need one timed variable resistor, right?
    I have no idea how to construct one, btw, but perhaps I can figure it
    out with a little research.

    Thanks again,

  9. Gordon Youd

    Gordon Youd Guest

    Hi, Nick,

    I was just throwing ideas at you.

    You could have a relay operated by a 555 timer and when the relay contacts
    open the leaves would fall, if you had made variations in the coil
    windings(no core, paper clip leaf becomes the core) and varied the leaf
    weights and put a large capacitor across the opening contacts the leaves
    would fall quite randomly.

    Hope you can understand my babbling.
    Best of luck.

    Regards, Gordon.
  10. In principle it sounds plausible (albeit time-consuming and expensive
    to build, I suspect). And, complementing the inherent variability of
    cores and magnets, you could add electronic randomness with several
    parallel 'magnetising' circuits. But have you done what I would expect
    to be the relatively simple test of trying *one* leaf/inductor pair
    before you go any further? It's all down (literally!) to that <g>.
  11. Can I take it that's a No, then?
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