Different Results Across SW Machines Head vs RDC vs Briffidi

[TysonMcMuffin]

I own a Head 3 in 1 Swingweight machine and a Briffidi SW1 machine. While both of them usually give the correct strung weight of a racquet, the unstrung measurements for a lot of racquets is usually really off, varying from 3-6 point off unstrung specs.

I bought a couple racquets off of pro stock tennis where they use an RDC Machine to measure swingweight and they had them listed as 300 sw unstrung. When measuring them unstrung on the head machine they measure 295 while on the briffidi they measure 299 (very close to pro stocks listed specs). I assume the people at pro stock tennis are very meticulous because all three racquets came spot on in terms of static weight and balance.

I measured the unstrung sw of the racquets on both a gosen sw machine and another head sw machine that a pro shop owns to ensure the machine I owned was calibrated correctly and all of the machines read 295 besides the briffidi which seems to read measurements similar to the Babolat RDC.

Another thing to note is that I believe aerodynamic racquets measure differently unstrung than straight beam racquets. I have two racquets, vcore 97hd and ezone 98 that are customized to match weight balance and strung sw. When measuring unstrung sw, the 97 read 295 while the ezone reads 290. When strung with the exact same strings, they both read 325 strung. If anything, the vcore 97hd should read higher because it’s an 18x20 racquet.

The head 3 in 1 machine does not have this problem. It reads both the vcore 97hd and ezone 98 at 290 unstrung and they both have the same sw when strung.

In conclusion; Does anyone with multiple swingweight machines such as a prince or dunlop experience the same thing. I’m only asking this because I want to customize some of my racquets to pro player specs but most customization pages on ig use either a dunlop or an rdc when listing unstrung specs.

 

[bfroxen]

I wrote this a few days ago but posting failed and I haven’t been able to access TT from any device. I thought it was down, but I found I can access it with cellular. No problems with any other site.

Not many people with multiple swingweight machines, I suppose. I have several, but they all measure the same. ;-)

There is likely some variance in the location of the pivot axis. I chose 10.0 cm for the SW1. I suspect that the Head 3-in-1 uses 10.16 cm (4 inches), but it would be great if you could measure that, @TysonMcMuffin . I remember reading somewhere that the Babolat RDC is slightly under 10.0 cm. The TWU calculator uses 10.0 cm. For a 300 kg·cm² racquet, the swingweight at 10.16 cm will be around 2 kg·cm² less than if measured at 10.0 cm.

The difference in differences between strung and unstrung racquets is likely due to air resistance. Most machines swing the racquet faster and through a larger arc than the SW1. I chose to keep the arc smaller to make the spring drive more linear. That's why the SW1 is so linear and accurate for measurement across a very large range (pickleball paddles, twistweight, etc.). It also reduces the effect of air resistance. Air resistance increases the period of oscillation which results in a higher-than-actual measurement.

There could also be variation in calibration rod accuracy. I'm pretty confident that the SW1 rod markings are within ±0.6 kg·cm² of actual (at 10.0 cm), but I have no idea about the other calibration rods.