Results 52 to 68 of 79
06-20-2012, 05:04 PM #52
Sorry, 0.523/40, the error is about 1.3%, just ctrl+c+v :P
06-20-2012, 05:28 PM #53
Your point about electronic machines not having settings for constant pull is pretty weak. Electronic machines do not have these settings because they do not need it. They do not pull every 5 seconds but every fraction of a second, and there is no setting for that because the faster, the better.
About my other post, I suggest we simplify things a bit. Let's just take time out of the equation, since your statements only talk about accuracy.
You say that cranks, in all situations, are more accurate than drop weight.
I say this is wrong, because if you pull only once with a crank machine at say 30 lbs, you will end up clamping the string at around 29 or 28 lbs. If you do the same with a drop weight, you will end up clamping the string at around 29.5 or more.
Then you say that you can pull multiple times with a crank to achieve better results so it is better than drop weight.
And I say this is wrong too, because you can do the same thing with a drop weight, no matter how hard it is or how much time it takes.
A crank machine can be as accurate as a drop weight if you make the effort, but in normal conditions and in the way that everyone strings in a practical manner, it is not the case. Hence, recommending a crank machine to someone who is looking for accuracy and consistency is just plain wrong.
Now I'm sorry, but if you can't agree with that, I'll just refrain from arguing anymore. It is nothing personal, however it is clear and logical to me that what I am saying makes sense and since it is what many people (from which many are engineers or extraordinary stringers) have concluded, I'm going to just stick with that. It will also allow both of us to go play badminton instead of argueing :P
06-20-2012, 05:32 PM #54
Look at the Stringway Constant Pull dropweight machine, the point is the
"Lifts automatically at the position of the tenionhead. "
But other dropweight has no that function. As the kwun said, small degree has not much influnce. So may be the lift angle is enough for most condition. The head could be lifted some degrees maybe 20degree?. That maybe equal to the lever droped when string be elongated.
But that is not mean dropweight is constant pull machine.
And notice that its string length is longer than crank too.
06-20-2012, 05:41 PM #55
Remeber, the constant pull is time sensitive. That mean constant tension for a contant time. 20lbs for 10s. Whether it could be replace by many times pull in one second, i'm not sure now, but i don't think it could be replaced.
Look at kewun and my reply to kewun, the angle and the length, that is more accurately than your presume.
06-20-2012, 05:44 PM #56
Now, only Stringway called his dropweight machine is Constant Pull, because of the "Lifts automatically at the position of the tenionhead. "
No other dropweight has that function. If you understand how the stringway works, you will understand why the dropweight has no constant pull, and stringway add a fixed function.
06-20-2012, 06:00 PM #57
06-20-2012, 06:07 PM #58
Look at the error caculated for dropweight and crank. Understand?
You just thought it is continue pulled, but it is NOT in correct tension. It is losing tension.
The crank is locked, but it is at correct tension. It is losing tension too.
Can you understand the two tension lose? They are almost same.
The error one is 1.5%, one is 1.3% for same string length, actually, string length at crank is shorter than dp, right? short lenth mean less tension lose, right?
As you said, if the string is elongated to 10deg, the r of the gripper is about 3cm.
10/360*2*3.14*3=0.523cm, it means the string be elongated about 0.523cm
For the dropweight machine, length of one string from the racket head to the gripper is about 40cm, if using a crank machine to pull the 40cm string, string elongated same, it is 0.523/40, the error is about 0.13%.
But for the crank machine, the string length from the racket head to the gripper is much less than 40 cm, it is much shorter than the dropweight, shorter string length mean tension lose less.
Originally Posted by kwun
one more point about the drop weight and the angle.
when the bar is not completely horizontal, the force is given by the following formula:
force = weight * cos(alpha)
the alpha is the same alpha that you listed in your diagram.
but if you look at how the value of cosine changes, you will realize that even when alpha = 10 degrees (which is quite a lot), cos(10 deg) is only 0.9848, which amount to a error of 1.5%. that is hardly of any concern at all.
06-20-2012, 06:13 PM #59
For example, the lever at 90degree, what is the string tension now? It's zero. That mean the string is too loose.
06-20-2012, 06:16 PM #60
The Stringway just using the head lift to fix the tension lose. To maintain the correct tension. If you understand that, you will know why the crank and dp lose tension is almost same.
06-20-2012, 06:17 PM #61
06-20-2012, 06:20 PM #62
The elongated string cause the lever not at the H positon. So Stringway make the elongated happened at the left, not at the right. understand?
06-20-2012, 06:21 PM #63
06-20-2012, 10:55 PM #64
This is like arguing with an autistic 10 year old...
06-20-2012, 10:59 PM #65
06-20-2012, 11:02 PM #66
Here I got another point. Thanks kwun, whether you are chinese, your caculate remind me.
According to the length between the racket head to the gripper. DP is too long than crank. String length too long mean the string will lose more tension. So gripper close to the racket is better.
06-21-2012, 07:51 AM #67
Dropweight query - I've been assuming that the tension for a dropweight machine is given by the calibration scale at the edge of the weight itself. So here, for instance, I would assume that the tension is 24LBS. Is this correct? Ta, smautf.
06-21-2012, 10:51 AM #68
In princple, it will be correct when the lever is at the H position. It's better to use a tension meter, like this.
You will see the tension is not excatly accurate, about 0.2lbs error, but the accurate is enough. Yonex es5 is 0.1lbs error:P
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