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Need Help With Vibration Experiments

  1. Jan 17, 2008 #1
    Hi,

    I am currently in the process of completing my final year mechanical engineering thesis, which compares the dynamics of damped drumsticks (not the chicken ones, the drum kit playing ones!) with those of a conventional, undamped drum stick.

    I now am up to the point where I need to devise an experiment to measure the intensity/amplitude of vibrations and also the time they take to decay. Where I am having trouble is my inexperience with experimental equipment and know-how.

    Some issues I can see myself having are;

    How to support the drumstick?
    - I figure I can either clamp the stick at either the end or where a drummer would grip the stick, or support it using thin string or wires that are attached to a structure above the stick.
    Would one of those methods be better than the other and why?

    Excitation Device
    - All I can think of is possibly an impact hammer and measure the subsequent reactions of the stick, however I am concerned that this might add a degree of human error.
    Would this be the best way to excite the stick?

    I am also having concerns about the weight of the drumstick and it relative light weight, compared to the force it is being struck with.

    Is there anything else I should look at? What would be the best way to measure the amplitude and rate of decay of the vibrations in the stick?
     
  2. jcsd
  3. Jan 17, 2008 #2

    FredGarvin

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    Science Advisor

    Welcome to my world. Testing takes a bit of a different eye.

    When it comes to supporting the drumstick, either way you presented would be arguably correct. I always try to fashion my tests the way the item is actually used. So I would argue to clamp the stick in a fashion that is closest to being held by a human hand. However, you do need to take a look at what effects that boundary condition will have on your results. Just make sure that what you are wanting to see will not be lost because of it.

    In terms of the excitation, it seems to me that you want to do what we call a "plink" test. You want to induce a s close to an instantaneous impact and watch for the results. We do that with turbine and compressor blades when we want to look for their natural frequencies. Essentially, with the stick very rigidly mounted, you "pluck" the end of the stick. This can be controlled by the initial deflection that you induce in the stick from its equilibrium point. It's kind of hokie, but the results are good. Plus it is very simple and requires no outside equipment to have to contend with.

    The best bet for measurement would be an accelerometer or multiples along the length. That would be more in line of a modal analysis. The other thing you could do, and is what we do, it to use a specialized microphone in VERY close proximity to the object. The microphone will pick up the tip vibrations that can be sent to an analyzer.
     
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