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Midlife crisis
11-19-2006, 06:16 PM
Can someone who is familiar with the procedure of calibrating a Babolat RDC please provide a brief explanation? I'm curious as to the various springs used to calculate the stiffness measurements of racquets, how the process works, and if the spring rate of these calibration springs is known.

And the same for the calibration of the swingweight measurement. Does it use the same springs or is there a different set?

And if the spring rate is not known, can you provide some basic measurements, such as the diameter of the spring, the gauge of the wire, and the number of turns per inch?

Thanks.

J D
11-19-2006, 07:18 PM
Midlife, it's been a couple of years since I've seen an RDC in action, but the mechanism for measuring frame flex was definitely mechanical, perhaps even hydraulic, and was digitally calibrated. It wasn't done with springs. I'm sure, though, that the process could be manually duplicated with a vice, table, brace, drop weights, and the proper calipers. You would just need to know the amount of pressure used in order to use the proper amount of weight and have a conversion table to figure stiffness from the amount of flection.

As to the swingweight measurement, my friend that owned the RDC machine (he used to own a tennis shop) said that he had to call the Babolat rep to send someone over to calibrate it. If there were any springs involved, it certaily wasn't apparent by looking. I seem to remember reading that the measurement is taken by gauging the resistance against a ball bearing mechanism, but I could be mistaken.

Someone like Greg Raven should be able to answer your questions in more detail.

Midlife crisis
11-19-2006, 10:18 PM
Midlife, it's been a couple of years since I've seen an RDC in action, but the mechanism for measuring frame flex was definitely mechanical, perhaps even hydraulic, and was digitally calibrated. It wasn't done with springs. I'm sure, though, that the process could be manually duplicated with a vice, table, brace, drop weights, and the proper calipers. You would just need to know the amount of pressure used in order to use the proper amount of weight and have a conversion table to figure stiffness from the amount of flection.

As to the swingweight measurement, my friend that owned the RDC machine (he used to own a tennis shop) said that he had to call the Babolat rep to send someone over to calibrate it. If there were any springs involved, it certaily wasn't apparent by looking. I seem to remember reading that the measurement is taken by gauging the resistance against a ball bearing mechanism, but I could be mistaken.

Someone like Greg Raven should be able to answer your questions in more detail.

JD, after your message, I've been searching and searching to try and find where I read that, and I finally found it. It's in the September/October 2005 RSI magazine, under "Your Equipment Hotline". It was indeed Greg Raven who did the question and answer section. Part of it says:

When taking measurements, the USRSA uses calibrated instruments. ... USRSA's Babolat RDC machine, which is used to measure flex and swingweight, is also calibrated: flex using Babolat-supplied calibration springs (which also allow calibration of the stringbed stiffness measurements), and swingweight with specially-weighted calibration racquets."

So, I was mistaken about calibrating swingweight using springs, but they are apparently used to calibrate flex and stringbed stiffness. Reading this again more carefully, it might be as simple as using the machine against these calibration springs. Since the spring rate, assuming it's a metallic spring, should be linear, we can figure out how the racquet stiffness rating system works.

J D
11-20-2006, 09:35 AM
Midlife, I'm sorry, I did misunderstand. I thought you wanted to try and duplicate the RDC mechanisms using springs.

Yes, Babolat does make calibration frames to set the swingweight, though I don't think it's a "do-it-yourself" job. Also, Babolat does use springs to calibrate the measurement gauge for the flex/string bed stiffness. I can't imagine that it would be any industry secret as to what what the specs are for the springs they use, so I'm guessing they would tell you if you emailed them directly.

Midlife crisis
11-20-2006, 10:03 AM
Midlife, I'm sorry, I did misunderstand. I thought you wanted to try and duplicate the RDC mechanisms using springs.

Nah, totally my fault I'm sure. Sometimes I get thinking about these things and my fingers disconnect from whatever part of my brain helped me to get straight D's in Language Arts. Though using springs to duplicate the RDC machine is something I hadn't thought of!

Yes, Babolat does make calibration frames to set the swingweight, though I don't think it's a "do-it-yourself" job. Also, Babolat does use springs to calibrate the measurement gauge for the flex/string bed stiffness. I can't imagine that it would be any industry secret as to what what the specs are for the springs they use, so I'm guessing they would tell you if you emailed them directly.

Thanks, I'll do that.