# Thread: 2003 Yonex rackets measurements

1. Originally posted by cooler
I didnt understand this question. I thought the table had showed how head heavy each racket compared to the cab20M. Ex. the balance point of AT700 is ~ 6% further up the racket than a cab20M.
the balance point of a racket is not very useful a measure on its own. the true static "heaviness" of a racket should be the moment generated by the racket, ie, the distance to the CG of the racket multiplied by its weight (N*m).

let's give an example, a 1m long uniformly thick steel rod may weight 20kg with a balance point at 50cm. while a 1m long plastic rod weighting 200g also has a balance point at 50cm. the steel rod has a higher moment and thus much harder to swing.

the same can be said about badminton racket. a 80g racket and a 100g racket with the same balance point, the 100g racket will be harder to swing. and thus the real value we need to look at is not merely the balance, but the actual moment which is a combination of the balance and weight.

2. Originally posted by cooler
that is not a sound conclusion. there are 3U MP100, 2U MP99, 3U cab22/cab20 Power, 3U MP88 out there which i havent got hold of but i'm confidence that their stiffness are comparable to each of their 2U's counterpart.
i wasn't making a conclusion, just merely an observation.

i am not convince about your claim though, it'd be an interesting experiment now that you have the setup...

3. Originally posted by kwun
the balance point of a racket is not very useful a measure on its own. the true static "heaviness" of a racket should be the moment generated by the racket, ie, the distance to the CG of the racket multiplied by its weight (N*m).

let's give an example, a 1m long uniformly thick steel rod may weight 20kg with a balance point at 50cm. while a 1m long plastic rod weighting 200g also has a balance point at 50cm. the steel rod has a higher moment and thus much harder to swing.

the same can be said about badminton racket. a 80g racket and a 100g racket with the same balance point, the 100g racket will be harder to swing. and thus the real value we need to look at is not merely the balance, but the actual moment which is a combination of the balance and weight.
i see i see However, just for completeness, the rod example u have highlighted is straight forward, linearity. For an objects with irregular shape, moment of inertia would still be different even when these irregular shaped and density profile object have similar CG location and weigh similarly. If we assume the rackets to the ideal case of the rod (linear system), then the cg * mass comparison is pretty straight forward. It was this issue of irregular frame shape that held me back of not doing the moment calculation

Before i make those calculation, please note the limitation of calculated moment of inertia from some excerpts that i got from a space industries measuring device manufacturer. Of course, the content contain some marketing messages as well. No , i do not plan to buy one of those MOI measuring instrument

Why measure Moment of Inertia The MOI of simple shapes may be calculated by well known methods. However, reducing complex shapes or compound objects to an assemblage of simple objects and summing the moments of inertia can lead to large errors. It is more practical and faster to accurately determine the MOI of complex objects or of objects with varying density by direct measurement.
Measuring MOI directly has these advantages:

Greater Accuracy - Typical errors in calculated MOI can range to over 30% due to simplifying the part shape, or making assumptions about average density. If hanging wire or trifilar pendulums are used to measure MOI, large errors result from multiple mode oscillations.

Cost Savings - Measurements can generally be made in a small fraction of the time required for exact MOI calculations. Cost savings in engineering time alone can quickly pay for the instrument. Furthermore, calculations do not account for manufacturing variations.

Quality Assurance - Military and industrial specifications frequently set limits on MOI (and CG location), where these parameters are critical to the performance of rockets, projectiles, and re-entry components

4. Originally posted by cooler
BRL, i didnt say the stiffness data presented would be the holy grail answers to all question about stiffness. Yes, it is static stiffness comparison, it suppose to be a guide. I did not claim to be a dynamic stiffness comparision. If you want a dynamic review, go read the racket review section, you will see the opinions vary much much wider than my data on static stiffness.

Even if i have a \$1,000,000 machine to do dynamic stiffness testing, new questions and doubt will come out of it. It will never ends. It like you asking answers to the 10th decimal place after i gave you data with 9th decimal place.
You said it was a real life comparison, when in fact it was a lab comparison. In the real world, you only experience dynamic stiffness.

Dynamic stiffness can be tested very cheaply. A small weight, pen, and paper is all you need. Since dynamic stiffness (not static stiffness) is the only number that matters and can be very cheaply measured, I don't see why it's unreasonable to ask for it.

5. Originally posted by bigredlemon
You said it was a real life comparison, when in fact it was a lab comparison. In the real world, you only experience dynamic stiffness.

Dynamic stiffness can be tested very cheaply. A small weight, pen, and paper is all you need. Since dynamic stiffness (not static stiffness) is the only number that matters and can be very cheaply measured, I don't see why it's unreasonable to ask for it.
i see. so are you volunteering?

6. Originally posted by cooler
i see i see However, just for completeness, the rod example u have highlighted is straight forward, linearity. For an objects with irregular shape, moment of inertia would still be different even when these irregular shaped and density profile object have similar CG location and weigh similarly. If we assume the rackets to the ideal case of the rod (linear system), then the cg * mass comparison is pretty straight forward. It was this issue of irregular frame shape that held me back of not doing the moment calculation

Before i make those calculation, please note the limitation of calculated moment of inertia ...
understood. but the static moment is closer an indicator than just balance point alone. if we have equipment limitations that disallow us to get to the true value, we just have to settle for the closest approximation within our constraints.

7. Originally posted by cooler
i see i see However, just for completeness, the rod example u have highlighted is straight forward, linearity. For an objects with irregular shape, moment of inertia would still be different even when these irregular shaped and density profile object have similar CG location and weigh similarly. If we assume the rackets to the ideal case of the rod (linear system), then the cg * mass comparison is pretty straight forward. It was this issue of irregular frame shape that held me back of not doing the moment calculation
Irregular shapes can be approximated to a rod if there is no angular rotation along the axis perpendicular to the rod. This is true for all strokes except a smash, in which there is a small 90 degree rotation that is negligible. Thus it's perfectly fine to approximate a racquet as a linear rod of non-uniform density. If you presume the hitter always hits in the same spot on the string bed, you can further approximate it as a point-mass or ball at some distance from the axis of rotation.

With either approximation, MOI is easy to calculate.

8. brl, obviously you had taken my words out of context. I could have reported stiffness in term of deflection per unit length of racket shaft. Real life meant stiffness in relation to a known or common reference point like a cab 20, in my case i didnt have a cab 20 so i used cab20M. If you are so adamant about knowing real life dynamic, just ignore this thread and go read the racket review in the BC section. I can also tell you how to experience real life dynamic stiffness but i doubt kwun would let me elaborate in BF

Dynamic stiffness can be tested very cheaply. A small weight, pen, and paper is all you need. Since dynamic stiffness (not static stiffness) is the only number that matters and can be very cheaply measured, I don't see why it's unreasonable to ask for it.

Well, let see you run some dynamic stiffness test on your rackets. I don't see why it's unreasonable for me to ask for it.

9. Originally posted by bigredlemon
Irregular shapes can be approximated to a rod if there is no angular rotation along the axis perpendicular to the rod. This is true for all strokes except a smash, in which there is a small 90 degree rotation that is negligible. Thus it's perfectly fine to approximate a racquet as a linear rod of non-uniform density. If you presume the hitter always hits in the same spot on the string bed, you can further approximate it as a point-mass or ball at some distance from the axis of rotation.

With either approximation, MOI is easy to calculate.
kwun, brl, i agreed.
I just want people here to understand the limitation of calculated MOI although it's very small in this case.

10. if i'm going to systematically report real world stiffness, i'd be sure to do that.

Page 4 of 22 First 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 ... Last

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•