I have been reading again ( ya I know........ sorry guys) and i have a question about measuring resonant frequency.

Is their a relatively cheap and easy device for measuring resonant frequency? I'm thinking maybe a timing light set up of some kind or something that counts how many times a laser/light beam is broken between two points as the rod oscillates. Is there anything easy and hillbilly proof that can be bought and set up for for under $100

I am very electronically challenged but I am thinking there has to be something easier than filming with a video camera I don't have or trying to count that fast ( Remember.... hillbilly proof). I really need some kind of mechanical/electronic device to measure that with if I am going to be accurate with it at all.

I am about to finish up an engraving table for my sister and the next personal project I am going to take on is to build myself a NICE CCS set up. I don't want to go broke but at the same time I want something more durable and convenient than a cardboard and coat hangers.

Thanks in advance guys

Ray

Ray,

I haven't thought through this completely, so bear with me. There exists digital signal processing software available for free or for very nominal cost that allows the sound card in your PC to be used as a spectrum analyzer. The frequency of oscillation my be pretty low in a blank, I'm just not sure yet, but if the frequency will pass through the input coupling capacitor on the sound card, it can be detected and displayed as a spectrum, hopefully with a resonant peak that the resonance point or points (harmonically related nodal frequencies or unrelated secondary resonances may exist).

The transducer for this might be as simple as a microphone with good low frequency response, or possibly as complex as a strain guage chip taped to the blank along with a low noise, low frequency preamp to feed the sound card. Again, I haven't played with this concept long enough to work out the particulars, but the sound card and associated analysis software available makes the PC one of the most sophisticated measurement systems available to almost anyone. Ham radio operators are just now starting to exploit the capabilities of these things for their use. Several big companies are marketing specialized software to take advantage of the inherent signal sampling and processing capabiliies built into even low cost versions of sound cards. Just a few years ago, the Analog to Digital capability built into a sound card would have cost many thousands of dollars and would have required thousands of dollars more in DSP capability. We now have this built into even the cheapest of windows PCs and Macs.

Hope this gets some discussion going. I'll try to do some investigation into the Software avialable and the frequencies or techniques necessary to get the information into our PCs.

Cheers.

Larry

You could use a LED and a phototransistor in a simple DC circuit. Everytime the rod breaks the light a multimeter could read it and give you a number.

Good morning Ray! I see that you will not be building any rods for the next several months. Here is a link that will undoubtedly get you started down the path of vibrations and complex analysis. When Emory wakes up this morning he will provide you with a link to a gentleman's writings that make some sense to all of this. He even makes and sells, within your budget almost, that will do exactly as you desire. I thought seriously about heading down this road when a couple of bass fishermen asked for "Shakey Head Rods" but I could not figure out how to wrap the device on a light blank so it could give a reading to the fisherman measuring just how bad his shakes really were.

[www.patentstorm.us]

Have a nice day!

Gon Fishn

It would seem to me that along with the challenge of measuring the frequency would be the need to flex each blank with exactly the same force to keep the readings consistent from one blank to another. For even the slightest difference could change the readings drastically

Morning Bill!

I have a Winston and a Scott that I am working currently on.... but I do admit that progress is going slow now that I am trying to re-educate myself on the CCS (and other things rod) and trying to revamp my rod building equip.

Its all part of the fun of the process. :-)

Ray

You can search the board archives for more information. Emory Harry has written extensively on this subject.

On the other hand, if you are simply wanting to compare blanks for purposes of response/recovery, and only need a realtive scale to go by, the Common Cents Frequency method should be right up your alley.

................

Ray,
John Kaufman builds several relatively inexpensive devices for measuring the resonant frequency of golf clubs and I have tested them and they work equally well for blanks and rods. His web site is [csfa.com]. If you want to check one of these out most golf club sales and repair places will have one. I have talked to him several times about making an inexpensive device for making blank and rod resonant frequency measurements but he is so busy making the devices for measuring golf clubs that he does not have the time.
The resonant frequency on some rods that are long and not very powerful, like some fly, rods can be measured by counting the oscillations by eye over a period of time determined with a stop watch.
I use an approach similar to what you suggested with a collimated light source, it does not require a laser, that shines on a photo transistor. Just two resistors could be used if one of them is a photo resistor. The two resistors in a series voltage divider with the output taken across the photo resistor and just a several flash light batteries in series as a voltage source would work. But I take the output of the photo transistor and run it into a storage oscilloscope and an electronic counter but that is only because I have the instruments. You could use an inexpensive electronic counter. If you can find an inexpensive counter. I would suggest looking on @#$%& for some of the older used Tektronix counters because some very good older counters are very inexpensive. If you use a counter you will have better results if you make the measurements in the period mode not the frequency mode because the way the counters are designed they give you much better resolution and accuracy in the period mode than in the frequency mode when the frequency being measured is very low like the resonant frequency of a blank or rod. Period is just the reciprocal of frequency.

Steve,
The amount of deflection has almost no affect on the resonant frequency if you deflect the blank less than about 1/3 of its length. You can trust me on this. I thought that it would have more affect than it does and have tested it on numerous blanks.

THanks Emery,

That Club Scout Jr he has for $100 pushes the limit of what I wanted to spend but it looks as if it would work very well.

I emailed him with questions on how it would work with a rod. I want to make sure I understand how it works before I buy one.

again thanks,

Ray

Emory;
I trust you!
I also value your opinions, and respect your thought process.

Some times I don't always agree with what you are saying, but none the less you have my respect.

Would that also be true when comparing between brand A and brand B or just in the same product lines?

Ray,
John Kaufmann is a very knowlegable guy. I am sure that he will answer any questions that you have.

Steve,
If I understand your question, the variables that determine the resonant frequency are mainly the power, taper, mass, length, and modulus of elasticity of the material. It does not make any difference whether it is brand A or Brand B.

Thanks Emory

This topic raised sometime last year. I think for about $20, you can get an item that radio control airplane enthusiast use to measure their propeller's RPM. I'm short on time but I think you can check @#$%&.

Instead of an absolute number, I just compare two blanks instead as I set them off. The resonant frequency should stay stable even if you pull the blank a bit more or less before release.

Mo