Manually Measuring Swingweight

[bfroxen]

That’s right, and I agree.
now, when do you think it is a good time to nudge Brian again to see if he has sorted the SW1 packing abd international shipping challenges? Lol

I hope I have the single-box packaging sorted. It's actually three boxes taped together with cut-outs for the calibration rod to span all three. The device will be in the middle box. I have boxes coming tomorrow to test it out. I was struggling to come up with a solution to protect the device without having to fill a huge void.

Packaging is the first step towards international shipping. I still need to figure out what I need to do for GDPR compliance before I start taking orders from the EU or UK.

 

[bfroxen]

I think it could. If someone had a calibration rod of 150.0 & 300.0 and I had a calibration rod of 160 & 310 who’s to say either is correct. I could fool my SW1 by telling my SW1 the rod was 165 and 325 in stead of using the values on the rod of 167.6 & 324.3. This would mess up my calibration but if I could match 2 rackets to the same value it would be good because they would both be the same whether they are the right actual SW or not.

I've tried to make the calibration rods quite accurate. Each one is measured individually (lengths, masses, and geometry, not relative to a "known" swingweight) and marked appropriately. In the Q&A section of the product page, I estimate that the values are ±0.6 and ±0.3 kg·cm² for the with-weight and without-weight configurations, respectively.

You're right that the calibration value wouldn't really matter if just matching racquets. If they measure the same, they're the same. But, if the calibration were way off, you wouldn't see the expected changes in swingweight when adding mass.

 

[PrinceYonex]

Ok, I received the SW1 and rod. Put it together, leveled, calibrated. All good. Really nice quality, the app is super easy to navigate. I really appreciate the thought that went in to making this.

So, I started measuring, and it seems like all my measurements are coming out 6-8 points higher than I expect. A Head Pro Tour 2.0 that my friend measured at 329 on a 3-in-1 swingweight machine came out at 336 on the SW1. A Yonex VCP 310 (2019 edition) that I have measured with the manual method at around 322 came in at 330. A VCP 330 (2018 edition) came in at 338, but I was expecting 332 from my own manual measurements. My son's Ezone 100L, which I haven't measured before, showed up as 317 (TW lists the average at 310). I have a few more examples I could list. And it's certainly true that all the other methods of prior measuring might have been inaccurate, but it's striking that all the values I'm generated from the SW 1 are showing up high. What's going on?

I rechecked the calibration, and even did it once more (along with a re-leveling) on a different surface. The swingweight measurements are consistently coming in at the same numbers -- so the machine is definitely consistent. But it also seems consistently high. Not sure what I might be doing wrong. I am releasing with a light hand, I don't have any unusual air currents passing through the room.

Any suggestions on what might be going on here?

 

[tim-ay]

Ok, I received the SW1 and rod. Put it together, leveled, calibrated. All good. Really nice quality, the app is super easy to navigate. I really appreciate the thought that went in to making this.

So, I started measuring, and it seems like all my measurements are coming out 6-8 points higher than I expect. A Head Pro Tour 2.0 that my friend measured at 329 on a 3-in-1 swingweight machine came out at 336 on the SW1. A Yonex VCP 310 (2019 edition) that I have measured with the manual method at around 322 came in at 330. A VCP 330 (2018 edition) came in at 338, but I was expecting 332 from my own manual measurements. My son's Ezone 100L, which I haven't measured before, showed up as 317 (TW lists the average at 310). I have a few more examples I could list. And it's certainly true that all the other methods of prior measuring might have been inaccurate, but it's striking that all the values I'm generated from the SW 1 are showing up high. What's going on?

I rechecked the calibration, and even did it once more (along with a re-leveling) on a different surface. The swingweight measurements are consistently coming in at the same numbers -- so the machine is definitely consistent. But it also seems consistently high. Not sure what I might be doing wrong. I am releasing with a light hand, I don't have any unusual air currents passing through the room.

Any suggestions on what might be going on here?

Because of the bevel on my PK butt caps, i was reading a little high on those at first. I wrap overgrip on these rackets slightly higher than the edge. You have to make sure that butt cap is firmly against the back stop…. In my case I had a mm or so from the over grip getting in the way. Make sure you are all the way back.

 

[PrinceYonex]

Because of the bevel on my PK butt caps, i was reading a little high on those at first. I wrap overgrip on these rackets slightly higher than the edge. You have to make sure that butt cap is firmly against the back stop…. In my case I had a mm or so from the over grip getting in the way. Make sure you are all the way back.

I’m trying to measure without overgrips, and the base grips aren’t covering the bottom of the butt. I just redid a couple, really jamming my racquet to the back, but I’m still getting the same numbers. The machine is very consistent! But I still am wondering if I’m somehow generating swingweights that are too high.

 

[jmnk]

If anything I would suspect that numbers given by a calibrated SW1 machine are actually the accurate ones. Because it ships with a calibration rod, and the manual /thread thread here puts do much emphasis on pepper calibration, spring conditioning, leveling, making sure the racket is mounted correctly etc.
Compare that with RDC. it does not even come with calibration rod(s). Who knows when or if these machines were calibrated. Do you also think people doing the measurements o multiple rackets for these published numbers actually take enough time to make sure they do it properly? I kind of doubt - they are likely just some average numbers of few quickly measured items.

 

[Power Player]

I agree with jmnk. If you put the rod on and get the exact sw reading (or at least the whole number) then the machine is probably better calibrated than the one at the tennis shop down the road.

 

[PrinceYonex]

If anything I would suspect that numbers given by a calibrated SW1 machine are actually the accurate ones. Because it ships with a calibration rod, and the manual /thread thread here puts do much emphasis on pepper calibration, spring conditioning, leveling, making sure the racket is mounted correctly etc.
Compare that with RDC. it does not even come with calibration rod(s). Who knows when or if these machines were calibrated. Do you also think people doing the measurements o multiple rackets for these published numbers actually take enough time to make sure they do it properly? I kind of doubt - they are likely just some average numbers of few quickly measured items.

This reasoning makes sense to me. But it’s going to take me some time to readjust my sense of swingweight, if my SW1’s numbers are to be believed. Seems like nearly all my racquets are at 330 or above, in some cases closer to 340. Here I thought I was playing closer to mid 320s, sometimes even low 320s.
They are just numbers, of course, but it’s strange to adjust one’s sense of the “swing feel” that a certain number corresponds to.
I haven’t even begun to worry about the twistweight measurement yet!

 

[Kozzy]

Got everything calibrated and set up. I'm sure I could do a bit of a better job, but post calibration my reading was 313.15 against 313.2 on the calibration bar. I'm guessing that's close enough? Hopefully so. I measured two stock Regna 98s, strung, with overgrip, and got 317 and 319. Weights and balances are pretty close on those two (327g and about 32cm balance) - no customization done to them. Then I measured up a couple VCore Tour 89s with Kimony leather grips and no other customization. One came in at 324 and the other at 333. Both of those are 345+ grams and roughly 31.5cm balance. As for the SW1 and the app, they are just awesome. Once you have it set up it is so easy (kudos to @bfroxen). I haven't bothered with measuring twist weight yet, as I don't know that I want to start worrying about that in addition to everything else.

 

[bfroxen]

post calibration my reading was 313.15 against 313.2 on the calibration bar. I'm guessing that's close enough?

Yes, definitely.

 

[Irvin]

Ok, I received the SW1 and rod. Put it together, leveled, calibrated. All good. Really nice quality, the app is super easy to navigate. I really appreciate the thought that went in to making this.

So, I started measuring, and it seems like all my measurements are coming out 6-8 points higher than I expect. A Head Pro Tour 2.0 that my friend measured at 329 on a 3-in-1 swingweight machine came out at 336 on the SW1. A Yonex VCP 310 (2019 edition) that I have measured with the manual method at around 322 came in at 330. A VCP 330 (2018 edition) came in at 338, but I was expecting 332 from my own manual measurements. My son's Ezone 100L, which I haven't measured before, showed up as 317 (TW lists the average at 310). I have a few more examples I could list. And it's certainly true that all the other methods of prior measuring might have been inaccurate, but it's striking that all the values I'm generated from the SW 1 are showing up high. What's going on?

I rechecked the calibration, and even did it once more (along with a re-leveling) on a different surface. The swingweight measurements are consistently coming in at the same numbers -- so the machine is definitely consistent. But it also seems consistently high. Not sure what I might be doing wrong. I am releasing with a light hand, I don't have any unusual air currents passing through the room.

Any suggestions on what might be going on here?

Are the numbers on the calibrate page the same as the numbers recodred On the Calibrate page in the app? Measure the rod again to made sure you get the same readings as recorded on the rod. You can calculate the approximate SW of your rod too. my rod is 56.1 cm long and weighs 283.56 g. The the inertia at the center of mass is mr^2/12 or 74.4 Kgcm^2. Because the pivot is 10 cm from the end calculate the offset from the center minus 10 cm, mine is 18.05 cm. Then multiply the square of the distance time weight of rod (18.05*18.05*.28356) and add the inertia calculated first. That should give you the approximate inertia of the rod within 1 point. If that’s what your rod is and what it measures your other machines is off. OIf you’re come up with a figure 6 points off then contact Briffidi support. If you got lost in the math let me know.

EDIT: You could also check the weight you add to the calibrate rod. Knowing the distance from the 10cm pivot you should be able to calculate the approximate inertia it adds to the rod. Make sure you calculate distant from center of the weight to the 10 cm point.

EDIT: Seeing bfroxen’s response below I see your problem. The rod’s length being off by 4.5 mm will increase the rod’s inertia a little but the weight being added 4.5 mm farther out evidently increases the inertia by about 6 kgcm^2. Anyway good to have your issue resolved quickly. If you have access to another SW machine you can measure the rod with and without the weight and record readings. These will not be as accurate as a normal SW1 rods but you can change readings on your present rod until you get a new one if you need.

 

[Irvin]

@PrinceYonex another idea. The tag end of your rod should be inserted into the cradle. It is only going to make about a 0.4 kgcm^2 difference but you want your calibration as accurate as possible.

EDIT: My tag is centered at the 10 cm pivot so it should not change the SW.

 

[bfroxen]

I was in contact with @PrinceYonex last night. Turns out that I made an error entering the rod length into my database. I entered 56.50 cm when it probably should have been 56.05 cm (checked at 22-1/6" with a yard stick). That changes the with-weight calibration value by 7.1 kg·cm².

I'm shipping a new pipe out today. I'm also going to start checking the calibration values on my SW1 to prevent this from happening again.

 

[PrinceYonex]

I was in contact with @PrinceYonex last night. Turns out that I made an error entering the rod length into my database. I entered 56.50 cm when it probably should have been 56.05 cm (checked at 22-1/6" with a yard stick). That changes the with-weight calibration value by 7.1 kg·cm².

I'm shipping a new pipe out today. I'm also going to start checking the calibration values on my SW1 to prevent this from happening again.

Just wanted to jump in here to say that @bfroxen has offered amazing customer service. The moment he saw that I was getting higher-than-expected swingweights, he reached out to me and started to troubleshoot the issue. In short order he figured out what the issue was and immediately offered to send a new calibration rod (incidentally, there was nothing wrong with the build of the original one, just a single measurement typo that was throwing off the calibration process).
For those who are interested in purchasing the sw1 but a little uncertain about it because this isn’t coming from a big brand, I can reassure you that build quality and customer care are excellent here. There’s an advantage when you are dealing directly with the guy who built the instrument and the app, not with a company rep.

 

[Irvin]

Just wanted to jump in here to say that @bfroxen has offered amazing customer service. The moment he saw that I was getting higher-than-expected swingweights, he reached out to me and started to troubleshoot the issue. In short order he figured out what the issue was and immediately offered to send a new calibration rod (incidentally, there was nothing wrong with the build of the original one, just a single measurement typo that was throwing off the calibration process).
For those who are interested in purchasing the sw1 but a little uncertain about it because this isn’t coming from a big brand, I can reassure you that build quality and customer care are excellent here. There’s an advantage when you are dealing directly with the guy who built the instrument and the app, not with a company rep.

Speaking of brand name SW machines. I would trust the accuracy of the Briffidi SW1 over all of them bar none. And the only thing I see going wrong is you phone breaks.

 

[jjs891]

Just wanted to jump in here to say that @bfroxen has offered amazing customer service. The moment he saw that I was getting higher-than-expected swingweights, he reached out to me and started to troubleshoot the issue. In short order he figured out what the issue was and immediately offered to send a new calibration rod (incidentally, there was nothing wrong with the build of the original one, just a single measurement typo that was throwing off the calibration process).
For those who are interested in purchasing the sw1 but a little uncertain about it because this isn’t coming from a big brand, I can reassure you that build quality and customer care are excellent here. There’s an advantage when you are dealing directly with the guy who built the instrument and the app, not with a company rep.

Good to know as I just ordered one for myself.
i was wondering though that the problem could have been adjusted on the phone numerically instead of replacing the calibration rod ?

 

[PrinceYonex]

Good to know as I just ordered one for myself.
i was wondering though that the problem could have been adjusted on the phone numerically instead of replacing the calibration rod ?

Yes, he talked me through those adjustments, but he also sent me a new rod because he wanted to make sure I was totally confident in the equipment. I appreciated that he went above and beyond to work with me.

 

[Irvin]

Good to know as I just ordered one for myself.
i was wondering though that the problem could have been adjusted on the phone numerically instead of replacing the calibration rod ?

The short answer is yes . But I like the idea that the supplier went that extra little bit to make sure everything was right.

 

[Power Player]

Just wanted to jump in here to say that @bfroxen has offered amazing customer service. The moment he saw that I was getting higher-than-expected swingweights, he reached out to me and started to troubleshoot the issue. In short order he figured out what the issue was and immediately offered to send a new calibration rod (incidentally, there was nothing wrong with the build of the original one, just a single measurement typo that was throwing off the calibration process).
For those who are interested in purchasing the sw1 but a little uncertain about it because this isn’t coming from a big brand, I can reassure you that build quality and customer care are excellent here. There’s an advantage when you are dealing directly with the guy who built the instrument and the app, not with a company rep.

How did you find the typo?

 

[PrinceYonex]

How did you find the typo?

I felt like I was getting high swingweight measurements, relative to numbers I had produced manually or with a friend's 3-in-1 machine. That was the starting point. So @bfroxen reached out to me, had me check a few basic weight and length measurements on the calibration rod; he checked those numbers against his own records of the one he had sent to me. There was a discrepancy in the length measurement, and that accounted for the higher-than-expected swingweights.

 

[Kozzy]

I've been trying, with extremely limited success, to match/customize my own racquets for years. I now see the #1 problem was that my SW calculations were absolute garbage. I'm sure they don't have to be, but I clearly sucked at it . Thanks largely to the SW1 (and the TWU customize tool), for the first time ever, my changes actually hit the mark! I was aiming for 328 SW on two different racquets, and I got it! Holy cow. So easy. I'm sure that a real racquet pro would not be impressed, but they pretty much feel the same to me, and I don't think I can tell the difference. Did it again with another set of frames as well, and got equally good results, in less than an hour! So amazing to have a simple, easy way to measure the swingweight that works every time, even for a clod like me.

 

[Dags]

I hope I have the single-box packaging sorted. It's actually three boxes taped together with cut-outs for the calibration rod to span all three. The device will be in the middle box. I have boxes coming tomorrow to test it out. I was struggling to come up with a solution to protect the device without having to fill a huge void.

Packaging is the first step towards international shipping. I still need to figure out what I need to do for GDPR compliance before I start taking orders from the EU or UK.

Course, if you need an international test subject for sending one of these...

 

[Irvin]

@bfroxen While on the subject of calibration rod, have you considered placing a fixed weight inside of one end of the rod? There would never be the issue of not getting the weight on flush, out of perpendicular alignment, and less wear and tear on the weight and rod. The user would just flip the rod end over end to change Inertia.

 

[bfroxen]

@bfroxen While on the subject of calibration rod, have you considered placing a fixed weight inside of one end of the rod? There would never be the issue of not getting the weight on flush, out of perpendicular alignment, and less wear and tear on the weight and rod. The user would just flip the rod end over end to change Inertia.

Yes, I considered that. The benefits you listed outweigh the downside of having to flip the rod, but I didn't come up with a good design to put something inside the rod in a way that's conducive to determining inertia from mass and dimensional measurements. I want to avoid having a "master" calibration rod and basing all other off that. I'm open to ideas...

 

[Irvin]

@bfroxen you said you were going to measure each rod on your own SW1 and if you assume a weight centered at 2 cm from the end of one end and about a 56 cm rod it would not be hard to calculate the approximate weight you need for a 150 kgcm^2 difference.

EDIT: 2 cm from the end is just arbitrary could be any Distance depending on material used.

 

[Irvin]

You could create a weight that has a lip at the bottom the same diameter as the OD of the rod, and the portion above the lip the same diameter and the ID of the rod. Then glue, epoxy, screw, or weld the insert into the rod.

EDIT: Depending on the fill in your plug you could add a heavier weight than you would have with filament and epoxy the weight inside the plug. But then you would need to stop and resume printing.

 

[bfroxen]

I am going to measure the rods on my SW1, but only as an error check. The calibration values will still be based on physical measurements. That rules out any kind of adhesive, as I can't be sure where it all ends up.

 

[PrinceYonex]

Ok, I received the SW1 and rod. Put it together, leveled, calibrated. All good. Really nice quality, the app is super easy to navigate. I really appreciate the thought that went in to making this.

So, I started measuring, and it seems like all my measurements are coming out 6-8 points higher than I expect. A Head Pro Tour 2.0 that my friend measured at 329 on a 3-in-1 swingweight machine came out at 336 on the SW1. A Yonex VCP 310 (2019 edition) that I have measured with the manual method at around 322 came in at 330. A VCP 330 (2018 edition) came in at 338, but I was expecting 332 from my own manual measurements. My son's Ezone 100L, which I haven't measured before, showed up as 317 (TW lists the average at 310). I have a few more examples I could list. And it's certainly true that all the other methods of prior measuring might have been inaccurate, but it's striking that all the values I'm generated from the SW 1 are showing up high. What's going on?

I rechecked the calibration, and even did it once more (along with a re-leveling) on a different surface. The swingweight measurements are consistently coming in at the same numbers -- so the machine is definitely consistent. But it also seems consistently high. Not sure what I might be doing wrong. I am releasing with a light hand, I don't have any unusual air currents passing through the room.

Any suggestions on what might be going on here?

I wanted to give a quick update. After noticing that I was getting high swingweights, relative to what I was expecting, @bfroxen helped troubleshoot the issue, including just sending me a new calibration rod. Great customer service. Anyway, I think I'm now getting accurate results, and the machine is extremely consistent in the number it outputs for a given frame. I'm not sure if I'm getting accurate twistweights yet, but here are a couple of my results. Out of excessive care, I made sure to level the racquet before each measurement. I don't think this really is necessary for swingweight -- the results don't seem to vary in significant measure.

VCP 310 Blue (3 gms at 10/2, leather grip plus OG, gut 1.3 /Ghostwire 1.22): 323 SW, 13.0 TW
VCP 310 Green (Stock with gut 1.3 /Ghostwire 1.22): 323 SW, 13.2 TW

I'm quite pleased that I had these two frames so well matched in terms of swingweight and, apparently, twistweight (but the static and balance are actually quite different, because one is stock while the other has a leather grip and weight in the hoop).

Head Pro Tour 2.0, stock, fb gut 1.3: 334 SW, 13.47 TW
Head Pro Tour 2.0, stock, gut 1.3 /Ghostwire 1.17: 329 SW, 13.49 TW

The swingweights on these PT2.0's are as I had expected, but I was surprised that the twistweights are only around 13.5. TWU lists this twistweight as 14.9!

 

[mad dog1]

@bfroxen fantastic product. Thank you very much!

 

[snoflewis]

mirroring @mad dog1's sentiments... awesome product @bfroxen

it's clear how much thought and planning went into this. every little detail has a purpose. i even love the angled edge of the lid for the BB compartment so that it makes it much harder to spill out. i'm really impressed. the app literally has everything anyone might need. really appreciate all that you put into this. anyone on the fence about the product or quality should really not be concerned at all.

now just need to find a case for it!

 

[snoflewis]

the SW1 has already saved me $20 in matched racket service fees. just need to switch rackets 13 more times and it'll pay for itself!

 

[Irvin]

the SW1 has already saved me $20 in matched racket service fees. just need to switch rackets 13 more times and it'll pay for itself!

Just $20? If you use the SW1 to match 2 or more rackets you’ve saved more than that.

 

[snoflewis]

Just $20? If you use the SW1 to match 2 or more rackets you’ve saved more than that.

i was referring to what TW charges just to measure the weight, balance, and sw of the frames and send you the ones that are closest in specs. they call it their matched racket service

 

[esm]

Just $20? If you use the SW1 to match 2 or more rackets you’ve saved more than that.

That’s what he said. So he has already save 20 bucks to start with, and he knows he will be able to save more when her uses the SW1 more often…..
Genuine question - how can the SW1 save the matching cost if you had to buy the racquets first with various QC specs. Unless you can return the racquets you do not want FOC…? No idea what the return shipping cost is anyway…

edit - meant to ask (for anyone), what is the popular method for matching racquets to your specs?

 

[tim-ay]

That’s what he said. So he has already save 20 bucks to start with, and he knows he will be able to save more when her uses the SW1 more often…..
Genuine question - how can the SW1 save the matching cost if you had to buy the racquets first with various QC specs. Unless you can return the racquets you do not want FOC…? No idea what the return shipping cost is anyway…

edit - meant to ask (for anyone), what is the popular method for matching racquets to your specs?

Man this is the US. Return shipping is free, haha. We may be fat and lazy, but we have free shipping.

 

[Power Player]

i was referring to what TW charges just to measure the weight, balance, and sw of the frames and send you the ones that are closest in specs. they call it their matched racket service

Yep..lol.

Although I can vouch for the TW service now that I have the SW1. My matched v7 Blades that I have up for sale are dead on the same weight SW and balance.

 

[snoflewis]

Yep..lol.

Although I can vouch for the TW service now that I have the SW1. My matched v7 Blades that I have up for sale are dead on the same weight SW and balance.

it's absolutely legit, it's just the last time i ordered rackets with it, it took 2 weeks to ship rackets out, and they're 3 hours away lol

but thanks to this SW1, i ended up ordering 8 VCP 97s

 

[Power Player]

it's absolutely legit, it's just the last time i ordered rackets with it, it took 2 weeks to ship rackets out, and they're 3 hours away lol

but thanks to this SW1, i ended up ordering 8 VCP 97s

No F'n way - 8?

 

[snoflewis]

No F'n way - 8?

shipping back 4 after measuring specs. sounds like there's some variation on the SWs

 

[Power Player]

shipping back 4 after measuring specs. sounds like there's some variation on the SWs

I like your style. Even keeping 4 to me is a big move, but yeah there is a variant for sure.

Id say around 321-327 stock SW will work. Mine is 3 grams overweight but barely needed any lead at 12 to really start playing well. For me the 326-327 SW number is money on this frame. That little bump of lead made a pretty big difference for me.

 

[AA7]

Man this is the US. Return shipping is free, haha. We may be fat and lazy, but we have free shipping.

 

[snoflewis]

That’s what he said. So he has already save 20 bucks to start with, and he knows he will be able to save more when her uses the SW1 more often…..
Genuine question - how can the SW1 save the matching cost if you had to buy the racquets first with various QC specs. Unless you can return the racquets you do not want FOC…? No idea what the return shipping cost is anyway…

edit - meant to ask (for anyone), what is the popular method for matching racquets to your specs?

free return shipping is fairly common in the US. it's also easier to match rackets with a similar starting point

 

[Irvin]

meant to ask (for anyone), what is the popular method for matching racquets to your specs?

That depends on the rackets being matched.

 

[Irvin]

free return shipping is fairly common in the US. it's also easier to match rackets with a similar starting point

There's always a starting point.

 

[esm]

That depends on the rackets being matched.

Ah okay. Can you give us an example or two - an idiot proof/some sort of calculation worksheet method(s) would be nice. Thanks.

 

[Irvin]

Ah okay. Can you give us an example or two - an idiot proof/some sort of calculation worksheet method(s) would be nice. Thanks.

No I can’t most situations are different. Sometimes I match weight and balance first, some times SW. but here is an example.

https://imgur.com/UF1KKQj

to begin I knew I had to match weight and balance by adding weight to the handle of racket #1 and I needed to add inertia to racket #2 by adding weight at the head. When I match weight and balance I like to use torque. t = mr and for SW (or TW) I = mr^2?

First I want to add inertia to racket #2 and I want the weight at 12 which is 67 cm but the butt or 57 cm above the SW axis. To determine how much weight m = I/r^2 or m = (309.59-207.51)/(57*57) = 1.19 g. This raises the balance and torque of racket 2 also from the initial to the final results.

Now I turn my attention to racket #1 weight and balance. r = t/m = (10381.33-10298.54)/(323.61-314.94.) Therefore I need to add 8.67 g at 9.54 from butt. In this case adding 8.67 g 0.06 cm from the SW axis (I = mr^2) gives me a negligible increase in SW.

if I knew the target specs I wanted to reach I would use a different procedure working with one racket at a time. Each situation may have totally different procedures.

 

[Irvin]

Ah okay. Can you give us an example or two - an idiot proof/some sort of calculation worksheet method(s) would be nice. Thanks.

Sometimes I find the lighter racket needs to have weight added to raise the balance and SW. That’s when I try to match weight at a point above the COM to raise the COM. I know if I add weight above the COM I will also be increasing the SW. I hope the weight needed to increase balance increases the SW to what is needed but that rarely happens. If the SW is close I leave it alone. But if I find I need to increase the SW it is sometimes possible without added additional mass.

Assume you add 5 g at the COM, balance does not change, but the weight and SW goes up. Another alternative would be to add 2.5 g 10 cm below and above the COM, in this case balance balance does not change, the weight change is the same as the previous assumption, but SW increases more actually (10*10*.005) by 0.5 kgcm^2? And if the mass placed 20 cm below and above the COM the inertia increase is (20*20*.005) by 2 kgcm^2. This is the point where I start losing people with math. Sorry but that’s the only way I can explain it.

EDIT: Imagine I had a bar with 2 weights at the center of mass, the bar would be balanced. i can slides the weights out towards the ends and the weight and balance would never change as long as the distance I slide each weight away from the center of mass remains the same. BUT inertia is a different story, the farther the weights go out the higher the inertia.

 

[jjs891]

@bfroxen
thank you for the great product. It is very consistent and easy to use once you learn.
just a quick question, do you recommend to unlatch the spring while SW1 is not in use or does it make any difference over a time ?

 

[bfroxen]

@bfroxen
thank you for the great product. It is very consistent and easy to use once you learn.
just a quick question, do you recommend to unlatch the spring while SW1 is not in use or does it make any difference over a time ?

You're welcome. I'm grateful to hear all of the positive feedback.

No, it's not necessary to disengage the spring for storage. The stress in the spring is quite low in the engaged position. Even when compressed solid (coil-bound), stress in the spring is barely above the allowable working stress for severe service (>1,000,000 deflections). Similarly, stress in the spring stops is quite low, so creep of the plastic should never be a problem. I'd probably avoid leaving a racquet or calibration rod mounted in the cradle for long-term storage, but even that would probably be fine.

Related, I had a customer ask about fatigue life of the spring. At the time, I only responded that I thought it would be quite long. Looking into it more, the stress during operation is well below the endurance limit, so it should never fail from fatigue.

 

[jjs891]

You're welcome. I'm grateful to hear all of the positive feedback.

No, it's not necessary to disengage the spring for storage. The stress in the spring is quite low in the engaged position. Even when compressed solid (coil-bound), stress in the spring is barely above the allowable working stress for severe service (>1,000,000 deflections). Similarly, stress in the spring stops is quite low, so creep of the plastic should never be a problem. I'd probably avoid leaving a racquet or calibration rod mounted in the cradle for long-term storage, but even that would probably be fine.

Related, I had a customer ask about fatigue life of the spring. At the time, I only responded that I thought it would be quite long. Looking into it more, the stress during operation is well below the endurance limit, so it should never fail from fatigue.

Thank you for the quick reply and info.