Babolat RDC
- Thread starter Yveskim89
- Start date
esgee48
G.O.A.T.
What do you mean when you say stringbed [DT?], frame flex [RA?] and SW are not accurate? If you are trying to match to unstrung specs, those are manufacturers' desired specs, not necessarily a frame's final finished specs. If you are trying to match to what is in racquet finder, those are averages. You should see if @Babolat Official can get his paws on documentation for calibrating the device. FWIW, you may need specialized equipment to do the calibration. TW also has a RDC, so you could ask them if they have the manual in a different forum. @TW Staff?
Irvin
Talk Tennis Guru
Yveskim89
Rookie
its show a very low reading.. like stiffness to 10-20 range, and swingweight around 100’s.. so i guess it needs calibration since it reads but not accurate.
uk_skippy
Hall of Fame
The manual doesnt contain the calibration instructions. If you want to calibrate the swingweight, then there are 3 calibration rods but they are likley to be very difficult to get hold of.
I have the calibration instructions, somewhere but IIRC it doesnt refer to the flex/stringbed mechanism.
You may have to send it to Babtec in France to get it properly calibrated. @Babolat Official will be able to confirm this
Irvin
Talk Tennis Guru
According to Josh the calibration rods are no longer available. The best you can do is use rackets with a known SW.
uk_skippy
Hall of Fame
Exactly. I have used my Prince Tuning Centre calibration rod, but it will give a slight difference in base readings. Its easier to explain with the RDC instructions.
Irvin
Talk Tennis Guru
That’s something I have always wondered about. How does any machine measure inertia on a parallel axis without knowing the Weight and balance. My guess is they are just measuring the resistance to a known force and coming up a a very good estimate of inertia. IMO if you’re using the same machine to measure SW whether it is exact or not you can still match rackets. But just because any machine says the SW is X value I’m not so sure how accurate it is unless you know it is well calibrated. First time I’ve heard though that different machines will give different base readings.
fritzhimself
Hall of Fame
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uk_skippy
Hall of Fame
The best way is to create 3 rqts that have the same measurements as the original rods; and to produce those using another RDC that is confirmed to be correct. Such as @fritzhimself has shown below.
I wasn't going to go into it, but I'll try and describe what I mean.
When you go into the calibration menu on an RDC you would use the rods to check the readings, and then adjust those readings so that it reads the correct 'check marks'. You would go thru the same method for each rod. When I use the Prince Tuning Centre Rod I do the same thing but the 'check marks' I have to use to align with the Prince rod's measurement are different. Similar to the way you'd check & calibrate your Star 5.
Yveskim89
Rookie
I will check it with Babolat Ph, i recently asked them about this, advised that i should send them the Babolat RDC for calibration. I hope someone from babolat can confirm this or Babolat France is the only way to fix this? By the way, im planning to buy the Head 3in1 swingweight machine,since Im havin no luck with the babolat one.
Babolat Official
Hall of Fame
Hi yveskim,
I don't want to be the bearer of bad news, but this may not be fixable unfortunately. I will reach out to Babtec in France to confirm, but they told me that if the RA flex/Stringbed stiffness portion is out of calibration, it is not repairable; definitely not by me at least. They might be able to fix it in France, but I will find out. The fact that the swingeweight values are so drastically off is not a good sign either. There is not that much adjustment to be done in the calibration procedure to move it up 200+ points as far as I'm aware. If I'm wrong, I'll let you know. DM me your email address and I will reach out when I have some news.
-Josh
Yveskim89
Rookie
Oh, so sad to hear this. Anyway pls update me regarding the calibration data - yvskm@yahoo.com .. thanks a lot.. i guess i just buy a brandnew head swingweight machine
Babolat Official
Hall of Fame
Hi yveskim,
Yes, it is too bad, and I'm sorry about this. I will let you know what I find out for you. My hope is we will develop a new version at some point, as it is a wonderful machine, but I haven't heard any news to that effect. Talk soon.
-Josh
Yes, it is too bad, and I'm sorry about this. I will let you know what I find out for you. My hope is we will develop a new version at some point, as it is a wonderful machine, but I haven't heard any news to that effect. Talk soon.
-Josh
Yveskim89
Rookie
I got the blue one, hopefully it can be repaired @Babolat Official, i hope to resurrect this machine^^. Thanks
Babolat Official
Hall of Fame
Hi Yveskim,
Good to know it's the blue one. And the issue may not be that it's out of calibration, but that the swingweight and flex units are damaged since the readings are so far off. I will let you know what I find out though. They are not in the office at Babtec at the moment, but are checking emails, so it may take a bit before I hear back.
-Josh
Yveskim89
Rookie
Thanks
If one knows the SW of the 3 Babolat calibration rods you can replicate them by cutting aluminium tubes at the right length. A tube of 25mm in diameter and 2mm thick would work well as it has a SW of apporoximately 340 for a length of 70cm (it's easy to make a very precise calculation). You then just have to cut exactly at the good length.
But since your readings are really off it might be a good idea to send it to Babolat for a check.
It is a spring which provides the known force. Also the axis for the measurement is exacly at 10cm from the end of the racquet which means that the machine measures directly the SW and there is no need to use the parallel axis theorem as in the TWU methode. So no mass and balance required here.
As far as I know the accuracy of the Head 3 in 1 Swingweight machine is +-0.5 kg.cm2 which means apporoximately +-0.15%.
There are calibration rods made of aluminium of precisly known SW values for the calibration of the machine. So in principle you get an absolute SW measurement and not a relative one.
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Irvin
Talk Tennis Guru
I'm aware of that. But I have measure the SW of several rackets using the cross strings as the pivots. I've used the crosses from the top to near the bottom. You can chart a bell curve from the top to about the 8th cross then it goes back up as you go down. How long the periods are is dependent on the inertia around the pivot and the distance from the balance point to the pivot. I'm not so sure about how accurate any method is any more only that it is repeatable. If it is repeatable it can be used to match rackets. As long as you use the same repeatable method all the time it should be good.
I use the same cross string every time, the same displacement at the start of the pivot, the same number of periods before I start the measurement, and SwingTool. My measurements are as repeatable as an RDC for less than $5.
2 years ago I gave up measurement calibration of RA, and DT (FLEX). Weight and SW works fine. On my blue RDC tip of racket go down about 2 cm and magic number is from - (minus) -60 to +2 and nolinear. I found 4 trimer screws. First too are for weight calibration. 3th and 4th are for RA. I have racket with RA 69 and I was trying combination of this trimers. Something deflection is 4mm, 8mm, and RA is 22, or -60 but not 69. Using this machines for swing weight only. This threed is great and I have new hope for help. Thanks
thx for the explanation. I'm still a bit unclear. What are those 'check marks'? I would imagine that during calibration you:
- use an object with a known swingweight.
- make RDC (or PTC) measure the sw.
- you adjust something until the measured sw is exactly what it should be - meaning the sw of a known object.
uk_skippy
Hall of Fame
When going into the RDC calibration settings, there are 3 readings that can be adjusted; and there are 3 calibration rods each with a different SW. Each reading need to be adjusted at the using a specific calibration rod. With the PTC, there is 1 rod but it covers 3 different SW readings by the use of a movable weight. This rod is designed to give readings of 100/200/300SW. These are different to the original Babolat calibration rods.
When I check my RDC I only use the 300SW of the PTC rod; but while the RDC will show a reading of 300 it does not align with the intended calibration settings when using the original rods. Its a bit like calibrating a stringing machine at say 25kgs, but not checking to see how accurate it is at 5kgs. The Star 5 & Sensor require checking at 4 points to get it fully calibrated; although if you were only stringing at 20-27kgs then you may not worry about accuracy at 10kgs.
Hope this helps, and not too confusing
thx, I think I follow.... Would you mind sharing that RDC calibration manual if you happen to have it?
2 years ago sent me on this forum:
Check the swing weight readings on all three calibration bars. The bar weights should be 252g, 315g, and 389g
Write down the values of each reading at all three bar weights
Next hold the test button (button5) for 3 seconds
Enter 1991 for the four digit code
Press the Etalon button (button 6)
Now you will be in the calibration screen
There will be 3 setting that you will see. The 1st setting will be the 252g swing weight, 2nd 315g, and 3rd 389g. Decrease or increase the value to adjust how much the initial reading was off. For example, if the 252g bar had a value of 254, then decrease the setting by 2.
Once all three calibration settings are adjusted, press the valid button (button 8)
Next turn off the machine and then turn back on to save the settings
In most cases you will have to go through the process a couple times to get all 3 calibration weights to hold the values. The RDC is accurate to + or -1
Check the swing weight readings on all three calibration bars. The bar weights should be 252g, 315g, and 389g
Write down the values of each reading at all three bar weights
Next hold the test button (button5) for 3 seconds
Enter 1991 for the four digit code
Press the Etalon button (button 6)
Now you will be in the calibration screen
There will be 3 setting that you will see. The 1st setting will be the 252g swing weight, 2nd 315g, and 3rd 389g. Decrease or increase the value to adjust how much the initial reading was off. For example, if the 252g bar had a value of 254, then decrease the setting by 2.
Once all three calibration settings are adjusted, press the valid button (button 8)
Next turn off the machine and then turn back on to save the settings
In most cases you will have to go through the process a couple times to get all 3 calibration weights to hold the values. The RDC is accurate to + or -1
thx, makes sense. That makes it a bit more difficult to do at-home calibration as the calibration bars have to be exactly 252, 315, and 389. I also wonder what is the theory behind doing the calibration at 3 different swingpoints.
Irvin
Talk Tennis Guru
The bars are 252 grams, 315 grams, and 389 grams unless I’m mistaken. Not 252-315-389 kgcm^2. If the bars are all equal length the center of mass for all three bars should be the same but I’m guessing they are not. That means all three bar have different mass, balance point, and SW. the periods of all three bars then will be different dependent on the distance from the 10 cm SW pivot to the balance point and the inertia of the three different bars. But yes that does make it difficult especially if you don’t have the bars which are no longer available.
The last time I talked to @Babolat Official the bars are no longer available but the do have rackets they can send out. But if the mass, balance points, and weight are distribution of the bars and rackets are not exact they won’t do you any good because you will just be fooling the machine’s program which will in turn uncalibrate your machine.
I suppose that is possible but it would be really convoluted. To calibrate the machine you need to use an object with a known swingweight, its weight does not matter. It would mean that Babolat RDC machine assumes that one uses Babolat calibration rods because that is the only way it could assume that 252grams rod is of certain swingweight (because it would be preprogrammed in the machine). I mean that would be a great business model as it requires that one uses Babolat stuff only rather than a generic calibration rod. Seems unlikely though.....
Irvin
Talk Tennis Guru
I agree with you for the most part, except for the part where you mention the great business model. Once you quit making the calibration rods because the $5,000 isn’t selling that business model goes right out the window.
That part about the SW is absolutely correct though. The software must also know the weight of the 3 bars, how far the balance point is from the 10 cm axis, and the inertia aka RW of the 3 rods. SW is determined by the period of racket oscillations against the known force in the RDC. The inertia of each of the rods alone is not enough to calculate SW. SW = I + (mr^2) where m is mass in Kg and r is the distance from the10 cm pivot to the center of mass.
fritzhimself
Hall of Fame
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The theory tells you that you need at least 2 bars. Indeed for the calibration of the machine one has to determine two parameters: the inertia of the machine itself (made of the system that holds the racquet, the vertical axis and all the components that move inside the machine) and a parameter proportional to the spring stiffness.
With 3 calibration bars you will increase the accuracy of the calibration especially if the SW of the bars are in the range of the SW of the racquets you want to measure.
Irvin
Talk Tennis Guru
Hummm. Kmocho above said “ The 1st setting will be the 252g swing weight, 2nd 315g, and 3rd 389g.” @Babolat Official which is correct weight or SW, and are the rods uniform in their length from end to end or not? @fritzhimself I’m thinking you have an RDC do you have the calibrations rods?
uk_skippy
Hall of Fame
I will once I've scanned them in. I've only got a paper copy at the moment
uk_skippy
Hall of Fame
I believe the calibration rods where never meant to be acquired/supplied by the user of the RDC but by service departments, so that the service departments would work on the RDC. A bit like car dealers would have access to service tools that independent garages dont. The other thing is that the machine wouldnt need to be calibrated unless it fell well out of its range. The calibration instructions mention clearing the memory of the machine on a weekly basis to avoid past results affecting current measurements.
oh yes, fully agree that two different calibration rods are required (I'm familiar with physics behind it). I'm not seeing though how the third one helps. If the machine is calibrated with two rods, the sw shown when measuring the third rod better be accurate already. I suppose to improve accuracy at a given range, as you are saying, maybe you are supposed to use either the 252 or 389 one plus the 315 kgcm^2 one - depending on whether you intend to measure lower end or higher end of sw range for rackets?
Actually you don't need the mass nor the balance of the bars for the calibration (and it's the same for a racquet ;-)).
Since the bar is horizontal the gravity does not play any role. The force is applied by a spring.
You don't need to apply the parallel axis theorem because the axis of rotation of the machine is at 10cm from the end of the rod which means that the machine measures directly the SW. If you know the SW of the rod you are fine.
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Irvin, you seem like a cool dude, and I see you are trying to help - but I'm afraid your understanding of how RDC measures swingweight is incorrect. So please do not take the below the wrong way....
the physics behind RDC machine is rather different than physics behind measuring swingweight using pendulum method (i.e. the TTW method, or what excellent swingweight app uses). RDC will give you a correct sw _without having to tell it what the weight of the racket is, or where the balance of the racket is_. It will however tell you the sw around the pivot point - whether that is 10cm from the end of the racket or not depends on how accurately you mounted the racket. But 'it' does not know it.
no it does not need to know that.
nope.
nope again
correct on that one.
nope.
the physics behind RDC machine is rather different than physics behind measuring swingweight using pendulum method (i.e. the TTW method, or what excellent swingweight app uses). RDC will give you a correct sw _without having to tell it what the weight of the racket is, or where the balance of the racket is_. It will however tell you the sw around the pivot point - whether that is 10cm from the end of the racket or not depends on how accurately you mounted the racket. But 'it' does not know it.
Irvin
Talk Tennis Guru
@jmnk I agree with what you’re saying but Kmocho above listed them as 252g swing weight, 2nd 315g, and 3rd 389g. I was thinking under the assumption the bars were identified by weight not swingweight.
That said if you know the inertia of a rod at a 10 cm point to be 315 Kgcm2. No matter how long or short the bar is, no matter what the balance is, no matter how much it weighs. The RDC will always measure the same period and show 315 Kgcm2 if calibrated right. But if all you know is weight then somehow the RDC must calculate the SW. it makes sense to me the bars are listed as SWs so the RDC can set the linearity of SWs through a range of SWs from 252-315-389.
That said if you know the inertia of a rod at a 10 cm point to be 315 Kgcm2. No matter how long or short the bar is, no matter what the balance is, no matter how much it weighs. The RDC will always measure the same period and show 315 Kgcm2 if calibrated right. But if all you know is weight then somehow the RDC must calculate the SW. it makes sense to me the bars are listed as SWs so the RDC can set the linearity of SWs through a range of SWs from 252-315-389.
For those interested - I've built home made RDC like swingweight machine. See http://tt.tennis-warehouse.com/inde...lly-working-one-total-cost-roughly-10.675711/
An extension of my RDC machine in the picture. https://photos.app.goo.gl/gyUUJLgETcpHj1Tk9
I measure mm. When I recalculate it via the index 0.1579 I get a pure strike RA 72. but on the RDC display it is 30.
I measure mm. When I recalculate it via the index 0.1579 I get a pure strike RA 72. but on the RDC display it is 30.
Babolat Official
Hall of Fame
Hi Irvin,
The specs you listed for the rods are swingweight, not weight, and they are different lengths; the highest swingweight is the longest, as you might have guessed. I do have racquets that have known swingweights that I can send as we only have one set of the rods in the US and cannot get more. The rods do not leave the office anymore
Josh
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