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Many thanks for your imputs! I have a complemetary question. Do you guys know if D1 schools use professional racquet customizer service for their players? My understanding is that it is uncommon. Which is a bit strange to me because those schools are really looking for the best possible...

I was wondering (naive question), do D1 schools have a stringer for their players or do the players stringing themself their racquets (or pay the stringing like every one else) ? I mean, they are training 3 hours a day, which means that they probably break at least once a day for the men, and...

http://tt.tennis-warehouse.com/index.php?threads/head-gravity.643574/post-15086953

On the G Pro I dont think so no. I just checked how much I use for the mains (Wilson Revolve, Stringway ML100) and it is between 6.25 to 6.5m which means around 21 ft... For the Tour I don't know, I don't have one at home.

Try Luxilon Big Banger Original. It should last much longer than 2 hours even on clay ;-)

It depends on the definition of "serious player" ;-). I have two sons playing at a decent level and, on average, they break strings 2 to 4 times a week (every 3 to 4 hours, using poly strings). At $25 per racquet it would mean around $4000 a year :eek:... Just for the stringing...

It is highly possible and no it would not defy the parralel axis theorem ;-). You should take a look at that paper, particularly the first two pages: https://www.sciencedirect.com/science/article/pii/S1877705814006146/pdf?md5=1f48b3ae0fb23a333877731a9253052c&pid=1-s2.0-S1877705814006146-main.pdf...

If you get 8 different readings using 8 different strings it means that your balance or/and the hang point are not measured accurately enough ;-). You have to understand that the parallel axis theorem is VERY sensitive to the balance and the hang point. A small error induces a large difference...

Sure. But the Swing Tool uses the parallel axis theorem to convert the inertia measured at any location into SW which is the inertia measured at 10cm from the butt cap. The only way to get rid of the parallel axis theorem, for SW measurements, is to put the axis at 10cm from the butt cap.

Yes, I tried and it worked. FYI, this thread discusses this way of measuring the SW (axis at the butt cap): https://tt.tennis-warehouse.com/index.php?threads/easy-diy-balance-board-and-accurate-sw-measurement.612001/#post-15078343 Can you post a picture of your setup? That might help to find...

Influence of the spring position on the Period VS Amplitude relation The position of the springs with regards to the axis of rotation influences the Period VS Amplitude relation for large angular displacement. For exemple, for a single spring design, the period will decrease as the angular...

Probably more reliable. A spring is someting extremily simple, reliable and accurate (in its linearity domain). An electronic tensioning system is much more complexe with different sensors, a motor etc.

You are confusing different things here. For ANY pendulum (gravity or spring driven) the period of oscillation is depending on the amplitude, even for a frictionless pendulum. It is only for very small angular displacement that the period becomes independent of the amplitude. It is what you...

Completely agree on that. Actually, while choosing my calibration rods, I was very careful so that their weights and lengths are very similar to a tennis racquet. rod 1, ~300g, 64cm rod 2, ~315g, 67 cm rod3, ~325g, 70cm I wanted them to behave as much as a racquet regarding SW measurements...

I measured more than 10 for my needs and the lowest SW I found on a GP was 295 unstrung... It is usually around 300. http://tt.tennis-warehouse.com/index.php?threads/head-gravity.643574/post-15086953

If you really meant unstrung, yes very easily. This is basically what Rublev plays. But you will get a 365g strung racquet... The thing is that the GP has one of the highest SW on the market so it will be 365g with a SW of at least 340 kg cm2 (strung).

Dampening By curiosity I analyzed the friction of my machine in different configurations. I wanted to know how much friction was coming from the spring fixation and also measure the effect of the friction of the strings and the air. Friction induces a dampening of the pendulum oscillations...

Customized and matched 4 GP to get the balance down to 31cm unstrung and the SW to 305 kg.cm2. Unstrung: 318.5g, 31cm, 305 SW. Ready to play : 343g, 31.8cm, 340 SW. Strings: Wilson Revolve 1.25.

Effect of air friction on repeatability? Indeed air friction could be the cause of the difference in repeatability of the measurements. To check it I measured 10 times in a row the SW (without removing the racquet or the rod from the holder) of: A strung Gravity Pro placed vertically ("SW...

I basically do the same thing as Crazydoc, I start measuring from the 3rd swing and average over 6 swings. The initial angle is around 20 degree. I tried to start at a lower initial angle but the results were not as repeatable probably due to the accuracy of the sensor. It is very important to...

SW repeatability and accuracy measurments I made some improvements on my machine, thanks to some very useful and efficient tips from Crazydoc (y), both on the hardware side as well as on the software side. It is “a personal challenge” as a 0.5 kg.cm2 or even 1 kg.cm2 SW accuracy is way enough...

Totally agree with fritzhimself on that.

I'm not confortable with the concept of a "first stringer". It's not like a racquet that you will change as you get better. High end stringer are much easier and much more confortable to use than cheap stringer . I would even say that really cheap stringer is a real pain to use. I personally...

l own a Stringway ML100 with flighing clamps and I am very happy about it. The tensioning system works amazingly well. I string between 1 to 4 racquets a week.

Sure, but one can say the same thing of a spring driven pendulum :) . Oh yes, I agree with you !! The repeatability of spring driven pendulum are not very good from my experience, and I'm not happy with what I get. That is why I would like to use a torsion spring. It could combine the...

Thanks. I currently have 0.6mm and 0.8mm springs. I will try M5 screws (y).

Indeed, for a gravity-driven pendulum, the force is constant but not the moment of the force which is what matters for rotating objects ;). The moment of the force is proportional to the angular displacement only for very small angular displacement (sin(X) = X) otherwise it has a nonlinear...

I don't see how a gravity-driven pendulum applied to SW measurments could be more accurate than a well designed spring-pendulum but I might be missing something (how do you deal with the influence of the racquet holder for example ?) . What I mean by a well designed spring pendulum is something...

What works the best in your experience? A screw of almost the diameter of the eyelet or something much smaller which reduces the contact surface? Anyway, I will experiment different things to improve the springs fixation. An hopefully to get to a systen which has a period independent of the...

I tried 4 or 5 different spring mounting points and indeed the best one I found, so far, is the parallel arrangement. It gives a very low level of friction. But the period is quite sensitive to the amplitude which, on my machine is a significant source of inconsistences. I don't yet give up the...