Racquet Mod Formulas: Matching Specs

[Amone]

Originally Posted by AJK1

There there don't cry Fitzroy, your off the hook. We all make mistakes, myself and Amone included. He just makes bigger ones.

PshPshPsh! What fun in life is there for little bambinos such as myself if not mistaking?

[Duzza]

Originally Posted by Amone

@ Duzza: The locations are measured in CM from the butt end, and they're the center of mass. So if you were to add the weight in 4 inch strips, you'd start 2 inches below the reccomended position. I'd also suggest rounding up to one decimal place, so that it's easier to find.

so you're saying to add Half the weight(23 grams) to both positions, 10 and 36 cm above buttcap?

[Greg Raven]

Originally Posted by travlerajm

The hitting weight is mathematically derived using the momentum balance, assuming that the swing has only translational motion at impact (neglecting the rotational component of the swing).[...]

If you look at the results from my spreadsheet, you'll see that I know what hitting weight is. On the OP's spreadsheet, however, I don't understand where that hitting weight is calculated, what the units of measurement are, and why his results are so different from mine.

[Greg Raven]

Originally Posted by Amone

[...]@ Greg Raven: As I've said a few times, I'm not done yet, because my formulae are the tiniest bit off. I don't see where it is, but I know it's there because in my tests, my swingweight usually ended off by about .23 points, hence not perfect. And the Effective Mass formula is calculated badly somewhere, I don't know where. I got it right on paper, but on Excel I had trouble with it. So regarding that issue: Agreed. Effective Mass is wrong.[...]

I often have a devil of a time translating known working formulae into functional Excel expressions, too. I usually wind up separating portions of a a long formula into small segments, each in its own cell, which allows me to see if any one portion is wildly out of range.

This is an ambitious project, so it's not surprising that it's giving you fits.

[Amone]

To explain, I 'derived' the formula from my copy of the Physics and Technology of Tennis, like most of my formulae. Originally, I had to make up a few 'control' variables, such as the location of impact on the racquet face, but then I noted that they had a more... direct way of doing it, so I instead used that as much as possible.

Before, I had kept my mouth shut because Ajm usually knows more than I do about this stuff, but that's how I got my results.

[MaxT]

This is great.

One suggestion/question.

It is easy to adjust total weight, but it is not easy to change weight locations. Most people wrap it on the handle and on 9/3 locations. So can you make the weight locations as inputs and make swingweight and final weight outputs?

[Amone]

Yes. I can. I can do this by linking you to Steve H.'s spreadsheet work.

[Duzza]

I personally like yours more. Steve's takes a bit of trial and error.

[Amone]

I created it to remove the trial-and-error. But Max asked me if there was a way to take a given weight at a given place and tell how it ended up.

[Duzza]

Yeah, it's good that there are 2 different ones, but I think the maths should tell you where to put it, not your choice :P. I'm gonna try the Safin Setup now

[Duzza]

Help me out please, they show a different swingweight, unless the swingweight at 10cm is different?..

[FitzRoy]

Originally Posted by Duzza

Help me out please, they show a different swingweight, unless the swingweight at 10cm is different?..

I don't know if the cause of your disparity is a problem in the formula or not; it might be. I do know that you aren't going to be able to get the Safin setup with the racquet you're using, because you can't increase swingweight by 37 adding 5 grams to a 348 gram racquet. If you want to match the swingweight and balance of the Safin setup, you'll have to do so with a higher static weight. That's one of the problems of matching his specs - it's hard to do with a lot of the stock player's racquets because they start out with a similar weight but have lower swingweights.

[Amone]

I do know one thing, and that is that your setup there is theoretically impossible; the racquet stops at 68.5, one of the weaknesses of my spreadsheets is that it allows that to come up.

Yes, I realised that there were disparities, though not that high. Perhaps there's something bigger wrong with mine, I'll need to get in touch with Steve H. or TravlerAjm about the swingweight formula for the original.

[Duzza]

Originally Posted by Amone

I do know one thing, and that is that your setup there is theoretically impossible; the racquet stops at 68.5, one of the weaknesses of my spreadsheets is that it allows that to come up.

Yes, I realised that there were disparities, though not that high. Perhaps there's something bigger wrong with mine, I'll need to get in touch with Steve H. or TravlerAjm about the swingweight formula for the original.

So I'll follow Steve's spreadsheet for this test and say it is 344 swingweight. Thanks, I noticed some of the figures go outside impossible too but that makes perfect sense. 5 grams pfft.

[andrew_b]

OK, help please? First, though, thanks for taking the time to provide this to the community! You've obviously put a bitof work into it, and you're not afraid to admit parts have discrepancies and to work to address them.

So, I played with it with my racket settings and a setup I'd like to try out:

weight: 340.48g
Balance: 32
Swingweight: 335

Final weight: 352.48
Final balance: 32
Final swingweight: 365
weight mass 1: 7
weight mass 2: 5

The above give me locations of (roughly) 14 and 57, which is OK.

I, too, get a pretty big difference in swingweight when I plug the starting values, weights, and locations into Steve's spreadsheet. It ends up saying the swingweight is 346.

Sorry I can't post the images like someone else did, don't know how to do that. Any idea why the swingweights are so different, or which one is closer?

Thanks,
Andrew

[BlackJesus]

First of all thanks for this usefull tool. The spreadsheet tells the location where adds the weights but I'd like to know how long the pieces of lead tape must be. Thanks

[BlackJesus]

I've got another question I've found on a previouse post (don't remember what) a link http://specgeek.50megs.com/LeadTapeO...ionApplet.html to this spreadsheet for calculating mod formulas. I'de like to konw if it's effective or not cause I'm not a math expert. Thanks a lot

[Amone]

If I could get that to work, BlackJesus, I probably wouldn't have done much more than adapt it to my own uses. But to be honest, I am completely uncapable of meeting that spec.

The weights assume 'concentrated mass.' In other words, if you must use strips, they can be as long (Or short) as you like, but make sure the center of them is at the point my tool specified.

[BlackJesus]

Thanks a lot Amone

[Amone]

If only I felt that helping you would truly give back to the learning I've recieved from the greats of Talk Tennis, or half of it, then I would welcome your thanks with the deepest gratitude. But I haven't, not with the sum of everyone whose seen this spreadsheet and been helped out.

So instead, I shall reply: "No, thank you."