Homebrew method of measuring RA

[wedge]

So I've become super interested in gathering as many stats as I can of the rackets I've accreted over the years. I've tried the TW University method of determining swing weight, and unfortunately the results are hyper-dependent on ultra-accurate measurements, any tiny discrepancy of which will throw off the final number dramatically. So, for swing weight I'm fine to get outside help, and I ordered a Briffidi to handle that part of things.

But stiffness is something I'm more than just curious about, since as I get older I'm becoming more and more sensitive to it. I'm fine to trust the TW stats on newer frames, but I have some older frames that don't have any published measurements anywhere. The cheapest solution is the Stringway Stringlab 2 -- I trust the mechanism of measurement it uses, but a) it's still more money than I wanted to spend, and b) flex measurement feels like a tractable problem I can determine without the help of a fancy machine.

I'm wondering if anyone has rigged together a simple system for doing this, or otherwise has any insight? I've come up with a bunch of ideas, but ultimately, I feel like the simplest solution would be to support the racket on both ends on books, then put like a 10lb weight on the throat, and measure the deflection as precisely as possible. Even if this would be an arbitrary scale, I feel like if I measure enough frames, and check in with some frames whose RA's are more or less accurately known, I can put together a workable scale of measurement that can be translated with reasonable fidelity into the RA scale we know and love. I sure ain't an engineer, so I can't intuit the force*distanceness of the whole thing, but honestly even a relative scale would be helpful I think.

I'm also just hoping that a 10lb weight won't be causing actual damage to these frames heheh ....

 

[fritzhimself]

It's old hat, but these guys did it.

 

[fritzhimself]

........here the measurements by Wilson

 

[Irvin]

ive Never tried it, but you could secure the handle, and lay a pointer on the head. Then add a 5 lb weight to the tip of the head and index how far the pointer deflects.

 

[wedge]

ive Never tried it, but you could secure the handle, and lay a pointer on the head. Then add a 5 lb weight to the tip of the head and index how far the pointer deflects.

Yeah this Wilson video has kinda inspired me -- doesn't this way of measuring flex make a bit more sense than the fulcrum flex that the RDC and Stringlab uses?

I'll rig it up and report back ...

 

[Roads_to_tennis]

So I've become super interested in gathering as many stats as I can of the rackets I've accreted over the years. I've tried the TW University method of determining swing weight, and unfortunately the results are hyper-dependent on ultra-accurate measurements, any tiny discrepancy of which will throw off the final number dramatically. So, for swing weight I'm fine to get outside help, and I ordered a Briffidi to handle that part of things.

But stiffness is something I'm more than just curious about, since as I get older I'm becoming more and more sensitive to it. I'm fine to trust the TW stats on newer frames, but I have some older frames that don't have any published measurements anywhere. The cheapest solution is the Stringway Stringlab 2 -- I trust the mechanism of measurement it uses, but a) it's still more money than I wanted to spend, and b) flex measurement feels like a tractable problem I can determine without the help of a fancy machine.

I'm wondering if anyone has rigged together a simple system for doing this, or otherwise has any insight? I've come up with a bunch of ideas, but ultimately, I feel like the simplest solution would be to support the racket on both ends on books, then put like a 10lb weight on the throat, and measure the deflection as precisely as possible. Even if this would be an arbitrary scale, I feel like if I measure enough frames, and check in with some frames whose RA's are more or less accurately known, I can put together a workable scale of measurement that can be translated with reasonable fidelity into the RA scale we know and love. I sure ain't an engineer, so I can't intuit the force*distanceness of the whole thing, but honestly even a relative scale would be helpful I think.

I'm also just hoping that a 10lb weight won't be causing actual damage to these frames heheh

The only question is that how can you measure this deflection sooooo precisely?
I agree with you method though....... Basically it's same as calibration, in which you first apply different known weights and then measure deflection. Here you can measure deflection and the correlate it to known RA values.
But, please note that the RAs we measure are for some specific point on the racquet. The RDC machine only measure RA for one point. A racquet has a different RA value at different locations ( This is happening due to different materials and different orientations of these materials used at different parts of frame). Basically, saying the a racquet is stiff might not be fully correct. You can make a racquet that is stiff from throat and flexible at hoop.
I can't remember the name, but I read a thread on the very same topic long time ago. In which a guy explained how prince tells RA values for different sections of a racquet

 

[anarosevoli]

I can't remember the name, but I read a thread on the very same topic long time ago. In which a guy explained how prince tells RA values for different sections of a racquet

I saved a picture of this:

 

[Roads_to_tennis]

I saved a picture of this:

Yes, this is it. I also never thought of racquets this way.

 

[ChanterRacquet]

Might as well go all out and create a flexibility profile the entire length of the racquet, just time consuming to do and might be easier to do photographically.

 

[PistolPete23]

Easy. Measure resonant frequency and convert to it an effective RA number.

 

[Irvin]

Easy. Measure resonant frequency and convert to it an effective RA number.

@wedge you can measure racket stiffness with RacketTune.

 

[wedge]

@wedge you can measure racket stiffness with RacketTune.

I've tried doing the frame-knocking with RacketTune, the app doesn't seem to like my knocking though, it doesn't seem to register properly. I'll continue experimenting with it for sure.

The only question is that how can you measure this deflection sooooo precisely?
I agree with you method though....... Basically it's same as calibration, in which you first apply different known weights and then measure deflection. Here you can measure deflection and the correlate it to known RA values.
But, please note that the RAs we measure are for some specific point on the racquet. The RDC machine only measure RA for one point. A racquet has a different RA value at different locations ( This is happening due to different materials and different orientations of these materials used at different parts of frame). Basically, saying the a racquet is stiff might not be fully correct. You can make a racquet that is stiff from throat and flexible at hoop.
I can't remember the name, but I read a thread on the very same topic long time ago. In which a guy explained how prince tells RA values for different sections of a racquet

With a decent pair of calipers and some reasonable attention to detail, I reckon we can get some fairly good results. Since I'm not an engineer I've asked a bunch of engineer friends, and they all seem to think that a homebrew contrivance is very reasonable and could have a solid expectation of good results.

This has all made me curious why Babolat, in developing their own standard, does measure over a fulcrum, rather than the Wilson method which seems to be a more real-world representation of racket behavior during actual play, and shock delivered to the arm.

I do recall seeing that amazing Prince chart from that thread where the Prince rep was just dishing all the dirt lol ... I'm not personally so interested in detailing all the stiffness characteristics up and down the racket, I basically just wanna know which old Prince 110's are flexier than which other old Prince 110's

 

[Rosstour]

........here the measurements by Wilson

Thanks for posting this. Really shows how special that racquet is. I play with one and can't imagine using anything else

 

[Irvin]

I've tried doing the frame-knocking with RacketTune, the app doesn't seem to like my knocking though, it doesn't seem to register properly. I'll continue experimenting with it for sure.

I’ll give it a try too to see if I can get it to work.

 

[Irvin]

@wedge FYI https://tt.tennis-warehouse.com/ind...-stiffness-rdc-ra-and-frame-frequency.425661/

 

[Roads_to_tennis]

Yeah... Wilson method simulates the racquet better than RDC. But RDC still give us a number for comparison.... I mean if RDC says racquet is stiff, I never felt it flexible ever in my whole life and I haven't seen any one saying that racquet is flexible in numbers but stiffer in actual.