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Electrical Engineering and Physics problem

  1. Sep 5, 2008 #1
    I'm building a simple demonstration toy, that shows a bee's wing in flight. It has a very fast moving part.

    In its most basic description it is nothing more than a pendulum which needs to rapidly cycle back and forth in about a 60 degree arc. (up to 150 beats per second). I've tried a purely mechanical solution but it would not hold up to the stresses at the connection points. A simpler solution is to eliminate the cam operation and have the pendulum with only one pivot point about 1/3rd the way up the shaft. The base of the pendulum would have a small metal piece that would be the driver for the pulse magnetic osillators at each end of the base arc swing. Unfortunately, I have no electronics experience and cannot even grasp the circuits and pulse devices needed.

    For most of you guys it is a simple matter of adding a 555 timer circuit, a capacitor, resistor and other techno-bits. I need help in figuring out how to get it to pulse, what to use to pulse the base of the pendulum and a simple circuit design.

    Any help would be greatly appreciated.

    I can see in this picture that at the base of this pendulum device there is some kind of magnetic motor which causes the pendulum to cycle back and forth very fast. I've got more weight, but the idea is similar.
    Pendulum clock
     
    Last edited: Sep 5, 2008
  2. jcsd
  3. Sep 6, 2008 #2

    MATLABdude

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    The clock, at it's absolute simplest is a motor that goes all the time, in one direction or the other, with a perpendicular shaft attached to it and some lights on the shaft that blink very rapidly.

    To get the reciprocating action, the motor turns one way, slams the shaft into something soft, and then the motor turns the other way, until it too slams into something soft. When the pulse train (alternating high voltage and low voltage) is high, the motor spins one way, and when low, it spins the other way. You might notice a lot of clicking or the appearance that the shaft is piling up on the ends, so you tune the duration of your pulse so that it just avoids slamming into the sides of the clock.

    Depending on what you've got, you'll probably need to use a relay (higher current), transistor (for the amateur, probably lower current) or motor driver (runs the entire gamut, and depending on your needs, these may range in price from not overly expensive to arm-and-leg) as your switch. There are many 555 Pulse Generator designs out on the internet, and you'll probably need to build yourself one of these to control the above switch. You may also need a power source depending on what the motor takes.

    Many of us got into this field by building canned projects, or circuits that had been designed by others, without a great deal of understanding. We got a basic intro to electricity, found some circuit diagrams (and how to read them), went down to Radio Shack (perhaps where we picked up a basic circuits book or something by Forrest Mimms), and went to town on our allowance / pay. After reading a bit more, we found we could customize these circuits to a small extent, and then we found some more diagrams that did other things, and maybe started stringing a few of them together, and repeated this cycle. In time, we found we could start designing our own circuits.

    That or we got an EE / Trade School education.

    Regardless, that's what you'd need to be a hobbyist (or, at the lower-commitment end of things, a basic understanding of electronics). If you're just looking to build a humming bird demonstration board, and don't really care about that, you might want to get a friend with electronics knowledge to give you a hand, or to build it for you. That or to buy something off the shelf (perhaps one of those aforementioned clocks).

    In summary, to build one of these from scratch (in a short time frame) with no electrical know-how may prove difficult.
     
  4. Sep 8, 2008 #3
    Thank you for your response MatLabDude. I know it will take me some time to complete this project, which is fine. I'm overdue in terms of learning more about the EE field, so this experience will be good for me. One thing that helps speed up this process is being able to ask cogent questions and get reasonable answers back like yours.

    Can you give me a link to an example of the electric oscillator design I should look for? I can put one on either end of the pendulum arc to pulse the base weight, or I suppose I could wrap the base in an arc pattern so the base is floating in a magnetic track which could change polarity. I just need to see some examples first to flesh out the design.

    Thanks again for your help.
     
  5. Sep 8, 2008 #4
    This is an example of a device which uses similar technology.
    Here is a rough diagram of the circuit design.
    I think I need a more powerful pulse device which can overcome momentum.
    Since this coil can only be turned on or off and the polarity is not reversed, the repulsive force on the wand is always in the same direction. The wand is held in place through a springy thin steel blade which is firmly affixed to the L shaped aluminium mound bolted to the circuit board. The springy steel blade has a strong tendency to return the wand to the vertical position. By pulsing the coil on and off an oscillation is induced in the wand which initially only moves back and forth a little but as the coil is pulsed the oscillation becomes wider.
     

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  6. Sep 8, 2008 #5

    MATLABdude

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    I'm guessing you would introduce the pulse on pin 11 of the LM339, and GND on pin 10 (or vice-versa?) This is a nice design, I don't know just by inspection how well it performs at higher speeds, however. Not that big a problem, you'd just need a stiffer spring (and possibly higher-torque motor).

    You don't introduce a more "powerful" pulse, as that's what the amplifier circuitry is supposed to do. Usually, the first signal you generate is pretty weak (few mA, if that).

    Since you ask nicely, here's a 555 tutorial:
    http://www.uoguelph.ca/~antoon/gadgets/555/555.html

    Good luck (and make a trip down to Radio Shack or wherever once you have your bits and pieces selected). Also don't forget a "bread board", and a basic electronics book.
     
  7. Sep 9, 2008 #6

    NoTime

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  8. Sep 9, 2008 #7
    Thanks again MLD,
    That web site was especially informative and breaks it down in simple terms I can understand. I'm going for higher speeds without a spring, so your right the higher-torque motor is a must. By adding a tail to the pendulum with a small metal piece, I can have two pulse pots at each end of the swing arc connected to the timer circuit, so timing the pulse will be critical. The higher speeds will also be a challenge.
     
  9. Sep 9, 2008 #8
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