Swingweight: App vs Prince PTC

[milowie]

NOTE: updated 8/5 to include results from Tennis Warehouse published method (http://twu.tennis-warehouse.com/learning_center/swingweight_calc.php).

I've been trying to match a few racquets using the available "at-home" measurement methods: Sten Kaiser's SwingTool app and the Tennis Warehouse published method.

While static weight and balance point are relatively easy to measure, I didn't have a lot of confidence in the swingweight results I was getting - so I found a local shop with a Prince PTC machine and compared the results.

Figured others may find this helpful, as well:

RACQUETS
Racquet - Static Weight - Balance Point
R1 - 363.38g - 30.480cm
R2 - 343.51g - 32.226cm
R3 - 336.10g - 32.385cm
R4 - 345.79g - 31.512cm
R5 - 360.92g - 30.480cm

SWINGWEIGHT RESULTS
Racquet - App - TW - PTC
R1 - 327.6 - 328 - 322
R2 - 330.4 - 337 - 329
R3 - 334.2 - 329 - 329
R4 - 328.2 - 328 - 326
R5 - 324.2 - 326 - 324

(NOTE: repeated R2 TW measurement of 337 to confirm; really that high / different than the other two)

PTC VS APP
Racquet (R) - Prince PTC SW - App SW - App +/- - App % diff
R1 - 322 - 327.6 - +5.6 - +1.7%
R2 - 329 - 330.4 - +1.4 - +0.4%
R3 - 329 - 334.2 - +5.2 - +1.6%
R4 - 326 - 328.2 - +2.2 - +0.7%
R5 - 324 - 324.2 - +0.2 - +0.1%

Average diff: +2.9 / + 0.9%

PTC VS TW
Racquet (R) - Prince PTC SW - TW SW - TW +/- - TW % diff
R1 - 322 - 328 - +6 - +1.9%
R2 - 329 - 337 - +8 - +2.4%
R3 - 329 - 329 - +0 - +0.0%
R4 - 326 - 328 - +2 - +0.6%
R5 - 324 - 326 - +2 - +0.6%

Average diff: +3.6 / + 1.1%

(right-click and view image; not sure why it won't show here)

I wasn't too concerned about the App or TW method being able to measure the correct swingweight - I was just hoping it would be off by a consistent amount compared to the PTC. If that were the case, as long as I had a target racquet to match to, it didn't matter if I knew the actual numbers, as long as they were the same.

Unfortunately, as you can see - the measurements vary inconsistently across the three methods. App and TW were, however, always equal to or higher than the PTC and they averaged about the same deviation - but this isn't helpful.

Whether you need an exact match, or won't be able to tell the difference in this variance range (or at least can fine tune by feel, if you are that sensitive) is the question to ask...

Here's my methodology:

Static Weight
Kitchen scale accurate to 1/100g

Balance Point
Balance on a dowel, measure distance using laser tape measure accurate to 1/32". Do this 3x to ensure accuracy.

Distance to Hang Point
I hung the racquet from the top string using two pencils and placed a block on top of the pencils (bottom of block aligns with bottom of string).

Placed a flat plate flush against the butt cap and measure distance from top of the butt cap plate to the bottom of the block on the pencils, using same laser tape measure. Repeat 3x.

Swingweight using the App
I hung the racquet from two pencils with roughed up ends to ensure the racquet would not slide.

Set sensitivy to 0.40.

Swing racquet in Preview mode and ensure red rectangle changes to yellow at correct point, and rectangle covers the handle exactly. Ensure camera is perpendicular to swing plane, and is at the same height as the handle.

Repeat 5x and average:

R1 - (326+327+328+329+328)/5 = 327.6
R1 - (327+327+328+327+329)/5 = 327.6 (repeated full process for R1 to evaluate repeatability)
R2 - (331+330+330+330+331)/5 = 330.4
R3 - (334+334+336+334+333)/5 = 334.2
R4 - (328+329+328+328+328)/5 = 328.2
R5 - (323+324+326+324+324)/5 = 324.2

Swingweight using Prince PTC
This was the tech's approach - measure until results are consistent:

R1 - 323, 322, 322, 322
R2 - 330, 329 329, 329
R3 - 329, 329
R4 - 326, 326
R5 - 324, 324

Swingweight using the TW method
I sat with the racquet swinging toward me, started at the closest point to me and counted 30 full swings. Repeat this three times, for a total of 9 10-swing measurements, and average to get the 10-swing measurement time used in the web form. Measurement data:

R1 - 41.92s - 41.82s - 41.83s = 13.952s
R2 - 41.45s - 41.42s - 41.53s = 13.822s
R3 - 41.26s - 41.30s - 41.27s = 13.759s
R4 - 41.69s - 41.72s - 41.55s = 13.884s
R5 - 41.86s - 41.87s - 41.86s = 13.954s

 

[CopolyX]

like your thinking...good job...
I am not familiar with the Prince PTC, thou.
remember all swing weight systems will also have a variance.
B. RDC and the A. AccuSwing : swingweight measurement is an average of three passes .
This is a more accurate system of measuring dynamic swingweight because it reduces the effect of inconsistent racquet release by the user(s).
From USRSA
As the chart shows, the AccuSwing registered slightly lower swingweight units than the RDC with lighter swingweight racquets, close to the RDC with medium swingweight racquets and measured lower than the RDC on heavier swingweight racquets. We don't know the reason for this mystery but are still checking with Alpha, Babolat, and our technical advisors.

The PTC:
http://www.tennisindustrymag.com/articles/2006/04/prince_precision_tuning_center.html

 

[esgee48]

https://tt.tennis-warehouse.com/ind...r-accuracy-when-measuring-swingweight.439949/

Anyway, TW uses their calculator to verify if their RDC is working right. I follow this when deciding where to hang. I know you used the SW App, but your variance is a little disturbing.

Could it be due to the rough up wood on the pencils? Given the differences, did the frames all have the same balance point and mass?

 

[milowie]

like your thinking...good job...
I am not familiar with the Prince PTC, thou.
remember all swing weight systems will also have a variance.
B. RDC and the A. AccuSwing : swingweight measurement is an average of three passes .
This is a more accurate system of measuring dynamic swingweight because it reduces the effect of inconsistent racquet release by the user(s).
From USRSA
As the chart shows, the AccuSwing registered slightly lower swingweight units than the RDC with lighter swingweight racquets, close to the RDC with medium swingweight racquets and measured lower than the RDC on heavier swingweight racquets. We don't know the reason for this mystery but are still checking with Alpha, Babolat, and our technical advisors.

The PTC:
http://www.tennisindustrymag.com/articles/2006/04/prince_precision_tuning_center.html

Thanks for this info and the link. Sounds like it comes down to feel and playability.

 

[milowie]

https://tt.tennis-warehouse.com/ind...r-accuracy-when-measuring-swingweight.439949/

Anyway, TW uses their calculator to verify if their RDC is working right. I follow this when deciding where to hang. I know you used the SW App, but your variance is a little disturbing.

Could it be due to the rough up wood on the pencils? Given the differences, did the frames all have the same balance point and mass?

Thanks for this link, as well. Following your note I added the TW results... did not bring any clarity. I would try the alternate swing position method, but the image with the formula wasn't loading.

Wrt the pencils, I misspoke - I actually wrapped tape around the edge as the paint was too slick. I don't think this had a material effect.

And to your second question - weight and balance were not the same; I've added these details, as well (but see no correlation to deviation).