Correction: Make that cpm instead of Hz. I'm an old EE who talked in things per second. I have however designed optical speed sensors and signal conditioning for many applications beyond 1000 Hz. We used to measure small deflection vibrations very accurately using a laser reflection device.
DEAN SYMONDS wrote: > 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.-.- -.-Spam and virus filtered by modusMail using Norman virus engine.-.-
