View Single Post
Old 01-08-2013, 11:50 AM   #99
Join Date: Jul 2009
Posts: 834

Originally Posted by Technatic View Post
Hi guys,
I think that it might be good to discuss our basic intention:

* I certainly understand that people with knowledge about physics will say that it is impossible to calculate the Swingweight of a racquet very accurately.

But the major question is: Do we want a system that makes it possible to compare racquets or do we need very accurate values of the SW?
completely agree here. In many, many applications an approximation is good enough. no one argues that. the only point of contention is where you stated in the earlier post:
"This system [e.g. spreadsheet where you enter weights at the ends, and length of the racket] certainly calculates the swing weigth."

it does not do that. it --approximates-- the swingweight, assuming that all rackets have the mass distributed the same way (i.e according to the same function).

Originally Posted by Technatic View Post
If we want to compare racquets we need a “measuring system” , with an accuracy that is as high as possible.

Another fact is that test results from different SW machines differ quite a lot, which proves that this is not an easy measurement to do.
So these machines are impressive and expensive but not accurate.
Honestly I never heard that before. Do you have a source for that claim?

Originally Posted by Technatic View Post
So if there is a much cheaper way to do a test, with about the same accuracy, there is a good reason to choose this test method. And a scale or even 2 scales are much cheaper than one SW machine.
sure, as long as you call it what it is - an approximation.

Originally Posted by Technatic View Post
What is our intentions with the SW advisor?
The idea of the SW came up because we advise the Dutch Tennis *** about material for young children.
- It should avoid that players play with completely the wrong SW and especially young children.
- We want to make it very easy for coaches to advise the right frame for a certain player.

The system does 3 things:
1. It advises a Swingweight for a certain player based on type of forehand, age and build.
I can't comment on this. I do not know if there's a biomechanical, medical, or other reason why a given swingweight would be 'the best' for a given player. Perhaps there is. what is the source of that claim?

Originally Posted by Technatic View Post
2. It calculates the SW of a racquet, when head- and throat- weight are entered. (Only have to weigh the weight at both ends of the racquet)
3. When the SW is too low it calculates how much weight should be added at a certain position to get the desired SW.

So for our purpose we need an advise system, a measuring (calculating system) and a way to customize racquets. This is what the Excel sheet (and the online version later) does.
so it is essentially the same thing that TW's own swingweight calculator does, right?

Originally Posted by Technatic View Post
And of course we wanted to know how accurate our “measuring” system is compared to the official machines.

Our conclusion out of these tests is that the difference between our system and official machines is not bigger than the difference between the different SW machines.

So the inaccuracy of our system is not worse than that of the official machines. And a difference of less than 5% of the measured value is not bad at all for a complicated test.

You will understand that we are not interested in theoretical solutions without practical possibilities.
could you provide some data on this claim based on 20-30 rackets, with varying characteristics: hammer type rackets, head light rackets, etc?

Originally Posted by Technatic View Post
There are different reasons for this:
* A swing weight test based on measuring the swing time of an object is a very logic choice. The SW can be calculated with one formula from the swing time
T = 6,28 *rt (SW/w*L)
this is not merely 'a logical choice'. this formula is based on physics laws. You can easily look it up why the formula is the way it is. It is --not-- an approximation, it gives you a swingweight value as per physics definition of what the swingweight actually is.

Originally Posted by Technatic View Post
* Calculating from the Head and throat weight is much more complicated.
calculating may be (due to the complexity of the formula) - but that is not the point. The point is that 'measuring' the oscillation time is way more complicated that merely measuring the weight. thus overall the method approximating the SW based on weight is way easier (but not exactly accurate).

Originally Posted by Technatic View Post
* Prince and Babolat sell these machines so it generates income.
yes. And these machines provide the functions that the weight-based formula does not. Is it worth thousands of dollars - definitely not to me. I go with Stoneage's app that gives me the exact measurement for $2.00
Originally Posted by Technatic View Post
* Prince and Babolat may do it with their machine Head seems to do it with the weighing system:

At 4.10 min you can see that they do the same kind of test.

Hopes this explains our intentions.
that video does not show anything that can be used in this discussion. It shows someone weighting a racket and than we see few numbers. I think we can safely assume those SW numbers are --NOT-- an approximation, but the results of actual measurements. if HEAD cannot afford Prince tuning machine i think they can at least get Stoneage's app.....

but again, for what you are doing the approximation is likely quite enough.
jmnk is offline   Reply With Quote