tag:blogger.com,1999:blog-4952460912398461727.post8424238818803387703..comments2024-04-02T18:09:47.857-07:00Comments on Teton Tenkara: Rod Moment of InertiaTom Davishttp://www.blogger.com/profile/18240935660681343164noreply@blogger.comBlogger24125tag:blogger.com,1999:blog-4952460912398461727.post-58916855194935527362013-12-10T10:49:08.982-08:002013-12-10T10:49:08.982-08:00Terrific. In an hour you could put up the Moment v...Terrific. In an hour you could put up the Moment values of 12 well know rods and create quite a buzz. I don't think I would go to a fly fishing show without a scale, tape measure and balance t-stand in my backpack. DWAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-41009059796803690202013-12-09T20:32:21.946-08:002013-12-09T20:32:21.946-08:00Excellent decision.
I will sleep soooooo much bett...Excellent decision.<br />I will sleep soooooo much better tonight.<br />Thank you.<br /><br />GregAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-44092624449587759402013-12-09T18:55:10.728-08:002013-12-09T18:55:10.728-08:00David W,
I received your comment but it will not ...David W,<br /><br />I received your comment but it will not publish for some reason. Yes, moment or torque is likely the better way to go than MOI for rods since true MOI is so complex to calculate. It makes no difference to me, moment or MOI. Both are just numbers that are not overly scientifically accurate (the way we calculate them), but moment (torque) is likely the better of the two. All we need the numbers for is to show comparison between rods and help further classify rods. In my mind absolute values are of relatively little benefit. <br /><br />From now on I'll go with moment (torque) instead of MOI. Moment (torque) = wt X r (where r is the distance from the rod butt to the center of mass or balance point).Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-30903582204084268482013-12-09T17:48:13.729-08:002013-12-09T17:48:13.729-08:00Tom, I think it would be better to promote the mea...Tom, I think it would be better to promote the measurement of the Moment rather than MOI. Measuring the Moment of the rod takes 5 minutes. It only requires two measurements: rod weight and distance to the balance point, or center of gravity, from the butt end of the rod. Followed by the simple multiplication of 2 numbers. All that is needed is an inexpensive scale, a tape measure, something to balance the rod across and a basic 4-function calculator. I think measuring Moment would be more widely accepted. And the numbers from more rods more easily compared by more people. <br /><br />From measuring the Moment of my own rods I know the ones with a Moment < 5 feel very light. And ones with M closer to 9 feel heavier. Looking at the Gamakatsu page I see several Seiryu or Keiryu rods with M values ranging from 8 to 32. <br /><br />I fear my posting of the link to the sexyloops MOI article has sent people onto a path into a complex way of measuring rods. That quickly confused or scared people off. But when I did a google search for "Moment of a fly rod". How to measure rod MOI web pages are what turned up. Not web pages about the Moment of rods. The sexyloops page seemed to be the clearest explanation I found. But to measure MOI correctly for a 9 section tenkara rod requires making over 20 measurements of weight and CG of each section plus other measurements of just the base or handle. And the use of complex math. I’m of the opinion that if you don’t calculate the MOI by following the full procedure it’s like saying you tuned up your car after only changing the fuel filter and one spark plug. If some people measure MOI one way and others another way or if some people measure CG from the butt end and others measure CG from a favored hold position then numbers measured will not be consistent. The Moment numbers will be as varied as the ratio numbers: 5:5, 6:4, 7:3, from one company to another.<br /><br />Gamakatsu calls it the モーメント指数 (Moment Index) or the formula itself is listed as モーメント指数計算式 ( Moment Index Formula or Moment Index Calculation Formula). M = the weight of the rod (g) × to the center of gravity from the rod butt length (cm) ÷ 1000<br /><br />You can find the formula listed that way on this web page, http://www.suikeikai.jp/keiryujitenmeikanspec<br />Where Gamakatsu calls them self the company of Moment notation, the revolutionary way by numbers to get a sense of the weight of the rod not understood by its weight or length alone. (or something close to that) <br /><br />I do not think Gamakatsu developed this idea alone. Though they seem to be its sole promoter. A 2007 document found on Fuji Hiromichi's webpage mentions the Moment of a rod as being important. But does not say how it is measured. Maxrod seems to be involved with designing bamboo rods. I do not find Moment mentioned on their English language webpage. But on their Japanese language page, under the topic Feel of the Cast, they talk about rod Moment, the Moment graph and the dynamic aspects of Moment, etc. It seems the measurement of the Moment of a rod has been used for some time in Japan. Though perhaps not known here.<br />Davidnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-3303449796058776522013-12-09T17:01:20.066-08:002013-12-09T17:01:20.066-08:00Thanks Craig!Thanks Craig!Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-6601755127940381302013-12-09T17:01:03.154-08:002013-12-09T17:01:03.154-08:00I'm working on such a chart.I'm working on such a chart.Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-24698704191156449412013-12-09T13:40:36.290-08:002013-12-09T13:40:36.290-08:00A thank you to Tom and Chris for applying a little...A thank you to Tom and Chris for applying a little science to rod measurements. The reality is niche products like fixed-line rods are going to bought online the majority of the time and measurable metrics are a great tool for the consumer.Anonymoushttps://www.blogger.com/profile/16764672674287577736noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-69561075243214174922013-12-09T12:08:41.785-08:002013-12-09T12:08:41.785-08:00I would love to see a separate chart for MOI of th...I would love to see a separate chart for MOI of the same rods in your RFI chart.<br />Just to see how different the two measures are. I can see ratings based on stars = user preference, the RFI to get a sense for ACTION, and then MOI to compare the perceived weight of a rod or FATIGUE/est. Swing Weight.<br />I'd especially like to see the numbers for the ONI and is there truly a similar rod for less that has the same RFI and perceived weightAnhttps://www.blogger.com/profile/14737839452227394850noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-86572854966436854662013-12-08T21:05:32.027-08:002013-12-08T21:05:32.027-08:00Denovich,
Your observations Are valid, but they r...Denovich, <br />Your observations Are valid, but they reflect "user variation". When I was using an Amago, I always gripped at the butt. Many others move to the middle of the grip, or top, for "finger on the rod".<br /><br />As it stands, the "axis of rotation" is at the end of the rod. An argument could be made that it should be at a "standardized" grip location, but good luck in setting that standard. <br /><br />For comparison purposes, when looking at a table of data, "end of rod" is OK, as long as "end of rod" is always used.<br /><br />GregAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-23822822747553335172013-12-08T20:18:31.960-08:002013-12-08T20:18:31.960-08:00Good thought. That makes it even more complicated!...Good thought. That makes it even more complicated! My head is starting to hurt!! ;o)Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-41944524226755041942013-12-08T19:57:33.965-08:002013-12-08T19:57:33.965-08:00Had a thought... isn't it the distance from ha...Had a thought... isn't it the distance from hand to CG that is really important and not butt to CG? Some rods are obviously made to be cast while gripping the butt. While others, like the 450 Honryu are fished most comfortably choking up on the handle, a finger on the shaft. Denovichhttps://www.blogger.com/profile/00780681393370499676noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-56393108013631619522013-12-08T19:03:33.584-08:002013-12-08T19:03:33.584-08:00Happy to contribute.
Experimenting with the 450...Happy to contribute. <br /><br />Experimenting with the 450 Honryu, if I add 140g, it has the same MOI as the Zerosum 7:3 360. :)<br /> Denovichhttps://www.blogger.com/profile/00780681393370499676noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-4566028629350170652013-12-08T16:22:27.089-08:002013-12-08T16:22:27.089-08:00Hey great!! I don't have some of these rods so...Hey great!! I don't have some of these rods so its really good to know their numbers!! Wow, the 43MF at 430cm is 105gm^2. That's something! I need to see how that compares to my LT44SF.<br /><br />Thanks again!Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-32902062009787195232013-12-08T16:00:24.034-08:002013-12-08T16:00:24.034-08:00Here are my figures as measured by me to the neare...Here are my figures as measured by me to the nearest cm or g. I've included both the Moment/Torque and the simplified MOI calculations. Sorry for the formatting (or lack thereof.)<br /><br />Rod Length Weight CG Moment MOI<br />Nissin Air Stage 390 396 42 105 4.41 46.305<br />Nissin Air Stage 450 Honryu 450 84 100 8.4 84<br />Daiwa Kiyose 43MF 384 86 81 6.966 56.4246<br />Daiwa Kiyose 43MF (zoomed) 430 86 111 9.546 105.9606<br />Nissin SP 450 441 57 111 6.327 70.2297<br />Kitoyaki 27 271 38 64 2.432 15.5648Denovichhttps://www.blogger.com/profile/00780681393370499676noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-43691458855361127232013-12-07T19:55:05.022-08:002013-12-07T19:55:05.022-08:00Sorry, it's mass TIMES radius squared. That...Sorry, it's mass TIMES radius squared. That's not a minus sign. I'll change it to (g)m^2, where g is grams and m is meters. Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-32764852483562542902013-12-07T19:02:24.191-08:002013-12-07T19:02:24.191-08:00Still, is there a typo when you went from mass TIM...Still, is there a typo when you went from mass TIMES radius squared to grams MINUS meters squared? If not, tell me how to do it in excel rather than on the web formula.Chris Stewarthttp://www.tenkarabum.comnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-54068649277805474552013-12-07T18:41:26.651-08:002013-12-07T18:41:26.651-08:00Chris,
Measure your rod in grams (g). Extend the ...Chris,<br /><br />Measure your rod in grams (g). Extend the rod fully and find the balance point (this acts as our simple center of mass or gravity point). Measure (in centimeters) from the butt of the rod to the balance point. Open the link to the MOI calculator (http://www.endmemo.com/physics/momentinertia.php). Change the units for "Mass of the Object" to g (grams). Input the mass (weigh in grams) of your rod. Change the units for "Distance from the axis" to cm. Input your measured balance point in centimeters. Click "calculate". This will give you a simple MOI for the rod. <br /><br />Mind you, this is just a simple, none hyper accurate, way of measuring MOI. I would not build a bridge with this method. But this gives you a simple easy way to compare the MOI between rods. The larger the number, the more force it will take to change the directions of the rod (like casting back and forth). I rod with a smaller MOI will be less fatiguing over time than a rod with a larger MOI.<br /><br />Others have suggested just using torque. Which is simply weight (in kg) times distance to the balance point. They both give you numbers you can compare. <br /><br />The best way to measure MOI for a rod is to take the rod apart and measure the MOI for each section then add it together, as is suggested in the Sexyloops article. I'm too lazy for that. The other way is to use integral calculus -- like I'm going to do that!Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-26697400214659819672013-12-07T17:55:20.083-08:002013-12-07T17:55:20.083-08:00Tom,
I have been interested for some time in a wa...Tom,<br /><br />I have been interested for some time in a way to measure swing weight or moment of inertia. However, for me to follow your formula, you will need to walk me through it (in excruciating detail).<br /><br />It has been a long time since I have had a math class or had to use more math than required to make change or calculate a tip. So, starting from the beginning, how did you get from I=m*r^2 to g-m^2?<br /><br />Also, what is g? Is it grams or gravity?<br /><br />Walk me through a calculation, leaving nothing out.Chris Stewarthttp://www.tenkarabum.comnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-7134358969151585032013-12-07T17:29:14.214-08:002013-12-07T17:29:14.214-08:00Sorry, I'm having some cold weather down time....Sorry, I'm having some cold weather down time. Can't get out and fish, but as you can tell, I need to!Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-86744555161406785352013-12-07T16:26:39.309-08:002013-12-07T16:26:39.309-08:00If this is angling. I'm practicing another out...If this is angling. I'm practicing another outdoor sport. Please, whoever wrote this article, can you give me a break? I've got lost after the first sentence.ramontranehttps://www.blogger.com/profile/06759765243116999884noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-51260052031240444392013-12-07T14:44:42.789-08:002013-12-07T14:44:42.789-08:00Me too, Jason! Me too!! I think I'll just stic...Me too, Jason! Me too!! I think I'll just stick to fishing!Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-34276574923911189692013-12-07T14:18:50.978-08:002013-12-07T14:18:50.978-08:00This post made me feel stupid. :(This post made me feel stupid. :(Jason Klasshttp://www.tenkaratalk.comnoreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-39315500701858730472013-12-07T10:23:32.019-08:002013-12-07T10:23:32.019-08:00Greg,
You are correct. But not being an engineer,...Greg,<br /><br />You are correct. But not being an engineer, I was just trying to find a simple and approximate way of showing differences between rods. What I didn't say above in my narrative is that for using the formula shown the rod must be assumed to be a point mass and not a tapered flexible rod with mass. It's cheating, I know, but then again its only an estimation and not hyper accurate. Also what I failed to say above was that the number generated is only for comparison to other rods and not calculated to be the the actual MOI for the rod in the true sense of what that means.<br /><br />You are correct and illustrate that that it is quite complicated to calculate the actual MOI for a tenkara rod. It can be done but more complicated math and science is needed. I was just going for a simple comparison between rods. Once again I failed!<br /><br />Thanks for your input Greg, I appreciate it!Tom Davishttps://www.blogger.com/profile/18240935660681343164noreply@blogger.comtag:blogger.com,1999:blog-4952460912398461727.post-39387956908690877762013-12-07T09:55:54.198-08:002013-12-07T09:55:54.198-08:00Tom,
The Moment of Inertia formula and calculator ...Tom,<br />The Moment of Inertia formula and calculator shown above is for a "point mass".<br />The MOI for a "uniform thin rod" is 1/3ML².<br />The MOI for a "tapering thin rod" is best found with process outlined in the "Swingweight" article.<br /><br />GregAnonymousnoreply@blogger.com