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Old 09-04-2012, 12:47 PM   #169
stoneage's Avatar
Join Date: Apr 2010
Location: Stockholm, Sweden
Posts: 243

Originally Posted by travlerajm View Post
The MgR/I formula can be used as a mass distribution design criterion as long as other design criteria are used along with it.

For example, when I design my own racquets, I use 3 critical mass distribution design criteria:
1. MgR/I = 21.0 (this assures a tuned forehand for an eastern to semiwestern grip).
2. MgR'/I' = 22.5 to 22.6, where R' = R - 10cm, and I' = the sw about the axis 10cm from butt. (this assures that my 2hb is tuned).
3. I' (SW) = 360 to 370. This assures that my serve will have maximum velocity without wearing my shoulder out. I start to lose speed on the serve if I go lower than that range (as measured by how high it hits on the back fence after a bounce in the service box). And if I go higher than that range, my serve is still fast, but my arm runs out of gas and I start to labor and lose accuracy after serving several sets.

Those 3 design criteria are in my opinion the most important.
Other design criteria, such as length, stiffness, string pattern, string type, head size, matter less and can be varied as long as I work within the first three constraints. If I want a bigger serve, I might go longer (and use SW at the upper edge of the range). If I want more control on groundies and volleys, I might go shorter.
Thanks for the clarification!
I have had two problems with MgR/I:

1. I have yet to hear an explanation why this parameter is relevant to the mechanical behavior of the racquet in tennis. MgR/I describes how the racquet swings freely in a gravitational field, i.e. like a pendulum. MgR/I=21 means that frequency of a racquet swinging from the but is 0.73 Hz. But unless you are building a cuckoo clock of the racquet I have difficulties to see the relevance. Gravity is the least of forces involved in a tennis swing. But if you have some explanation that could shed some light on this I would be most interested (no irony intended).

2. There are an infinite number of racquet configurations that fulfill MgR/I=21 most of them very strange and unplayable. So if you use only that to find an optimal racquet you could easily go wrong.

However, you say that MgR/I should be combined with a certain swingweight. And then it becomes something different entirely! By saying that MgR'/I' = 22.5 and I' = 360 to 370 you are saying that MgR' should be around 8200. And MgR'/I' (and MgR/I) has disappeared.

So your design criteria are:
1. setting MgR' (or MgR), which is the static force (moment) you feel when you hold the racquet in the handle parallel to ground.
2. Setting the moment of inertia (swingweight) which is good description of the rotational behavior

So there is obviously no need for MgR/I at all, which I think is fine since the two above criteria are better.


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Last edited by stoneage; 09-04-2012 at 12:50 PM.
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