RDC machine but what about a RA machine?

teachingprotx

Hall of Fame
Being a diagnosed racket o holic since 2001. I’ve always loved getting the specs from an RDC machine . All the cool gadgets on the machine is amazing. Yet it’s amazingly simple to work. Swing weight test . Balance , weight etc.. but as I’ve become a super geek I’ve come to realize that one thing that tells me most about the frame with one of the RdC’s capabilities is the flex test .
Matter of fact it’s the only one I care about , as We can manipulate everything else. Even the flex to a degree .
So.. how cool would it be if bab or some other .. company made a machine that gave us just the RA flex test number ..
Maybe someone already does and I don’t know it ?
 

golden chicken

Professional
If I remember right, the RDC just basically bends the frame, so I guess what you'd need to know is how much force is being applied and how the amount of deflection translates into the RA number we all understand.
 

dr325i

Legend
RDC = racket diagnostics center (machine)
RA = scale that indicates the flexibility of the racket (0-100 or whatever, where lower number means more flexible)
RDC measures weight, swingweight, racket flex (RA scale), string bed stiffness, maybe a few other things

I don’t think it would be feasible for Babolat or whoever to produce the machine that has one set of sensors (that measure), the microcontroller that calculates and displays the result, and other circuitry at any cost savings to the consumer.

plus, to do appropriate racket customization/matching, you need more than RA value
 

Tommy Haas

Hall of Fame
You could probably do it the low tech way. Get some racquets with a known RA. Not published RA, but actually previously measured. Clamp the grip to the edge of a table and use a heavy weight with strings tied to fixed points on the hoop and somehow measure how much deflection there is. Since you have multiple samples to test against, you might be able to determine that for every centimeter of deflection is 1 RA point. You can bet the hoop/frame will flex because if I'm picking up balls, and I load up the entire stringbed with just tennis balls, I can definitely feel the frame flex on me. Use a 5 pound weight and I'm sure you can visually see the deflection and find a way to measure it using a level and a compass. Maybe even using an iPhone AR app.
 

esgee48

Legend
Use something like Wilson's Stiffness Index. The frame is clamped and supported at the handle. A known weight, IIRC it is either 5 Kg or 5 lbs is attached to the tip. The deflection is the SI, which is the flex of the entire frame, not RA which is measured at one spot. Soft frames had SI ≥ 7. Medium frames had SI between 4 and less than 7. Stiff was below 4. That's if my memory is correct.
 
I find that pressing my thumbs against the upper hoop, with my fingertips around the lower hoop, and bending with handle against my knee to be a reliable indicator of relative flex for me.
 
Use something like Wilson's Stiffness Index. The frame is clamped and supported at the handle. A known weight, IIRC it is either 5 Kg or 5 lbs is attached to the tip. The deflection is the SI, which is the flex of the entire frame, not RA which is measured at one spot. Soft frames had SI ≥ 7. Medium frames had SI between 4 and less than 7. Stiff was below 4. That's if my memory is correct.
I believe you're right, and I think those SI numbers were used in conjunction with frames, like the Hammer 2.7 had a 2.7 SI.

I'd like to see flex measured three ways. All with the handle braced and first with the fulcrum underneath the throat just past the handle, second with the fulcrum underneath the midpoint of the frame, and third with the fulcrum half way up the hoop. I think having those would give a representative picture of flex along pretty much the entire length. After enough measurements, I think it'd become clear where flex is important to which aspects of the feel of a racquet.

Not something I think the manufacturers would be willing to do. It'd take an external resource like Tennis Warehouse.
 

Kevo

Legend
Seems like the most realistic flex rating would be done with a setup that can actually apply force similar to the way hitting a ball would. Maybe a first attempt at a machine like that would be to put the handle in a clamp and have the handle apply a force linearly perpendicular to the frame while a ball sized immobile pillar resists at the middle of the string bed. The amount of travel past zero of the handle clamp would give you a rating on some scale, maybe just mm or something.

If that actually seemed to give useful comparative info between frames maybe it would be good enough. If you wanted to enhance the rating you could build the handle clamp implement to work with forces in different directions so you would be able to get deflection measures in multiple dimensions.

A benefit and drawback of this machine would be that you'd actually be measuring the deflection rating of the frame and strings. This is good in the sense it should be more like what happens when you actually hit with the racquet, but it would also vary dramatically based on the particular frames string setup.

To overcome that drawback you'd need some sort of string stand-in for mounting and testing frames with no strings, but I'm not quite sure how that would work and still be accurate in terms of force application to the frame from the point of view of a ball impact. I think it would be doable with a jig that was something like a piece of circular leather with a suitable number of strings attached to it that would be temporarily mounted in the frame. It would probably need to have quite a number of strings or maybe some nylon straps that would wrap around the frame and clip on. They'd need to be easily adjustable and quick to mount while also being safe for the frame.

Anyway, just a though.

If anyone wants to license my idea let me know. :)
 
@Kevo Good idea if it can be executed. Since frame flex is in almost all cases greater than string flex, any mounting system as a proxy for strings which has flex will mask frame flex. That would probably include something inserted into the string holes, as it would be hard to isolate grommet compression/flex from the system. And with a single measurement, it's still hard to distinguish why one racquet with the same flex rating as another can feel so different.

It was several months ago when the forum dissected that marketing video for the Clash. They told some half-truths in that video because being fully accurate would be too confusing for the general public. That's probably why there's still a single flex number and not some way to describe flex along the entire frame.
 

Kevo

Legend
And with a single measurement, it's still hard to distinguish why one racquet with the same flex rating as another can feel so different.
Just changing strings can make the same racquet feel like a different racquet. Putting some sensation in a Pure Drive and giving it a good walloping for a couple of hours on court can make it feel pillowy if the strings don't break first. So yeah, it's definitely a hard problem, but I don't think we know yet if there could be a single measurement that was a good proxy for the feel of flex a frame has. Right now the measurement we have is very crude and not really all that analogous to hitting a ball. Maybe it is a better measure than I think, but I don't really have anything to compare with yet so I don't know for sure.
 

Tommy Haas

Hall of Fame
I think on the newer Babolat RDC machines you can change the fulcrum point. I think the default location was right above the throat on the bottom part of the hoop on 27" frames.
 
@Kevo You are quite right about the effects of changing strings. Probably stiffer and more elastic strings transfer strain to the frame in different ways that may also affect flex. It's a complicated issue and my original thoughts of getting just three discrete frame measurement points really don't address the effects of strings in any way.
 
A few years ago I made some of my own measurements in a similar way to the Wilson si method. I clamped the handle over my kitchen countertop, with the head cantilevered out. I suspended a 2kg weight (a half gallon orange juice jug) from the center of the stringbed. Then I used a meter stick to measure the downward deflection of the tip in mm.

I did this with the weight suspended in both the direction normal to the stringbed (x direction) and parallel to the stringbed (y direction).

I found that the dx/dy ratio (where dx is the x deflection and dy is the y deflection) correlated strongly with the subjective spin rating from the TW playtester reviews.

The higher the dx/dy ratio, the higher the spin score.
 

Kevo

Legend
Guess we don't have any stringers on this thread? Check out the Stringway Stringlab 2.
That's quite the logical leap considerings stringers have no need for a Stringlab to string racquets. In fact they have never needed to know about or do business with Stringway. Not to mention the Stringlab provides multiple measures and not just RA as requested by the OP, but it's a good mention regardless because the price is fairly reasonable.

Me personally, I "measure" all my frames RA by bending them across my chest now. If I can't get a good bend on a frame I know it's not for me. The first time I bent an F200 across my chest I knew I was going to be pleased and I was not wrong. That frame is sweet.
 

loosegroove

Hall of Fame
That's quite the logical leap considerings stringers have no need for a Stringlab to string racquets.
True, was a gross generalization. But the "regulars" who frequent the stringers sub-forum, have probably come across the Stringway Stringlab in various threads.
 
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