I've been using an optical cell for over 10 years to measure shaft vibrations well over the 1000 Hz point. I use voltaic cells that only cost less than $5 and terminate them properly. I recently broke the cell and had to replace it with a new one I bought from Digikey. I'm not at home so can't give particulars till I get back in March. I read the frequency using a digital sampling scope and usually read the period for a 6 cycle sample. If I can't get flat plane vibration to measure, I go to a one cycle period measurement and repeat it and average the results. Also at the higher frequencies I have seen a high damping so that trying to measure several cycles can cause problems because the crossover amplitude changes due to the reduced amplitude of the oscillation. Here again I go to averaging single cycle measurements.
The scope probe gives reasonable loading to the cell so I haven't even had to get design a loading network to get better response time from the cell. The rise and fall of the scope trace are mainly limited by the actual movement of the shaft and edge effects on the light source. It would however be pretty hard to make an optical sensor to detect the analog deflection accurately. Here I believe a load cell would give the best results. With 1 GHZ computers I would think could give a pretty good frequency estimate of even a heavily damped shaft. FWIW DeanS I'm John Kaufman wrote: > Hi Tom, > I was intrigued by your email. I've never tried to read high frequencies > with my Club Scout analyzer which is optical so I thought I'd give it a try. > I took a steel shaft for an iron and put an hunk of plastic on the tip with > a hole thru it that weighed 87 gram. It consistently read 514cpm. I then > slid the weight up the shaft stopping along the way and read consistent > readings (1 or 2 cpm) all the way to 833 cpm. The unit is limited to 999cpm. > I didn't go that far, my thumb was getting sore, but I'm sure I could have. > Cheers, > John K > ----- Original Message ----- > From: tom wishon <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Wednesday, January 15, 2003 10:11 AM > Subject: RE: ShopTalk: Shaft Zone Profiling > > > Alan and Al: > > Al has it right on the basics for sure for testing the stiffness of > > shafts in different places all along the shaft. One frequency reading > > taken only by clamping the butt end of the shaft is never going to > > reveal the real playability for any shaft. That concept came to me back > > in about 1995 when a company called Excel was making graphite shafts of > > different names (models) but stating that for consistency sake, they > > were adopting one common frequency for all their R's, all their S's and > > so forth. Being a descendant of Homer Simpson in terms of my thought > > patterns at times, I uttered an audible "DUH and DOLT" and scratched my > > head thinking, "well then how the heck could these be different shafts?" > > And with that, we started testing for stiffness at different locations > > on the shaft. > > > > The main problem with this in the beginning was that none of the > > frequency analyzers were able to measure the whole shaft in one > > consistent "feed-through" manner because their counter methods were > > either optical only or the chip in the board only read up to 500-600 > > cpm. To really see the shaft's profile you need to be able to read up > > to well over 1000 cpm and in a non-optical pick up mode because when you > > have only 12" of the tip sticking out of a frequency analyzer, the shaft > > is oscillating so fast and with such a subtle amplitude that an optical > > pick off unit can't "see it". > > To help get better at this, that was why I worked with some brighter > > minds than mine to make that load cell/strain gauge frequency analyzer > > that was created for Golfsmith to sell - the one where the sensing > > mechanism for the oscillation of the shaft was located under the clamp > > of the unit. And no matter what, that is still the best frequency > > analyzer in the component supply business today and beats the heck out > > of any optical unit at least when you want to do rudimentary zone > > stiffness measurement. To help make this more affordable for clubmakers > > the unit was made with the board and strain gauge set up to read a max > > of 600cpm. > > > > So that's why in the beginning the testing was done with only three > > measurements coming down from the butt and then switching the shaft > > around to make one measurement by clamping the tip. Not the best for > > real observations of this total bending profile of a shaft but at least > > a start. > > > > I will tell you the best work I have seen done in this area has been > > done by John Oldenburg, the VP of R&D with Aldila. With their technical > > acumen (and money!!) they have created a frequency analyzer that will > > read well over 1200 cpm so they can take a shaft and use the SAME tip > > weight and keep clamping down from the butt so all readings are done > > from one end of the shaft down, rather than to have to do a 180 with the > > shaft in the clamping unit. John's work in this area was what created > > the ONE shaft, which really is one of the only "family of shafts" that > > truly changes trajectory from a real visible standpoint to the eye when > > you use it. His work is all 'in-house' but I had a chance to see it > > this past year when I was continuing my work in this in a little > > different direction for plotting bending profile more accurately. > > > > It is possible to make decent shaft to shaft comparisons of the total > > bending profile using a "reverse the shaft in the analyzer" method - it > > just makes it a little harder to logically see in the brain when the > > graphs begin to slop up and then dive down for the tip section results. > > I will say that in the work I have continued in the past year on this > > that one of the things I did that helped me to see more about the total > > bending profile of one shaft to another was to change to a 454g tip > > weight and then to do 6-7 readings down from the butt with 4 readings up > > from the tip. More data points certainly helped allow me to see things > > that I never saw in the relationship of shafts. > > > > Use of the 1 lb weight was only done to "slow down" the cpms so that I > > could clamp farther down the shaft before I exceeded the 600cpm level of > > my analyzer. In truth all of this work is only "comparison" so as long > > as all data is gathered using the same methods, it is then comparable > > for seeing differences. Also, PING and the old Fenwick companies both > > used real heavy tip weights for years in their frequency testing of un > > assembled shafts, so this was another reason I opted for using the much > > heavier weight. And all the work I do for ordaining how I design shafts > > now is done on the raw and cut shafts with this 454g tip weight now. > > > > The real secret to uncovering the data of real shaft to shaft comparison > > is truly having as many data points as you can have on each shaft so > > that you can take one graph of a shaft and overlay it on another and > > then see how it differs ALL ALONG THE SHAFT'S LENGTH. From that I can > > say that in the past year I have been able to see things that I hope to > > get the time to write more about to make things a little more clear in > > fitting. For example, to really create shafts that are better designed > > to meet specific swing movements of golfers, the whole business of A, R, > > S, X as we know it is going to have to go out the window - by that I > > mean we are all now tuned into thinking that if we take a 45" driver for > > example, and put it into our frequency analyzer with a 5" butt clamp > > dimension and get a reading of 250cpm, that is an "R". And so forth for > > the other letter code flexes by looking for @10 cpm changes up and down > > from that. > > > > But if you want to make a shaft that will be well suited for a golfer > > who really needs to have a higher flight without losing much in ball > > velocity to truly gain more carry distance, you might have to make the > > butt end with a 260+ cpm and then the center and tip sections with a lot > > more flexibility so that in essence, you "freeze the butt" to allow the > > other 2/3 of the shaft to "kick" the ball up. And vice versa to make > > the butt lower in frequency with changing the tip firmer also does a > > similar thing (sorry for the totally non-tech terms there, but they > > describe it better). So in that case if you take shafts designed like > > this and do only a butt clamp and see that an R might be 240 or 260 > > something, your first inclination will be to say, "well this is a piece > > of C___ shaft because the frequency is not what it is supposed to be > > for an R" > > > > The only other way you do it is with a drastic profile change as John > > Oldenburg chose to do with the Aldila ONE - in that case the geometry of > > the shaft is "freezing" a part of the shaft to allow the other one to > > almost bend "independently" to do its job. And the other way is with a > > type of "composite splint" that could be put on the shaft in different > > places, which is something you will also see in the not too distant > > future for shaft design. > > > > Anyway, I have to get back to work and stop dribbling on too long about > > this - suffice to say you sucked me in with the commentary on Shop Talk > > going to zone stiffness because it is a real interest area for me that I > > can't avoid!! Sorry for the length of this again - > > > > Tom W > > > > -.-Spam and virus filtered by modusMail using Norman virus engine.-.-
