I'm from beijing, china, and doing some research about stringing machine. Recently I found there has a confused concept in how to choose the stringin machine. Someone thought that dropweight is more accurate than crank because of the Constant Pull. But after reading some paper about the constant pull and dropweight, such as "The_Importance_Of_Constant_Pull.pdf", i think it's a wrong concept about the dropweight with constant pull. The accurate stringing machine choice is: Electronic >> Crank >> Dropweight >> Awls/Puller The crank is working same as electronic, crank using hand and brain, electronic using moto and programmed chip. I think the Constant pull mean 1.Constant tension, 2.Continuous pull In "The_Importance_Of_Constant_Pull.pdf", it said "Mechanical Constant Pull (CP). There are 2 different mechanical CP systems: 1) Drop weight systems, which have the quality that the tension is the same for every angle of the lever." But I think the dropweight is not a constant pull machine. Because the string tension is not same when the lever holding in each angle. 1. The string will be elongated slowly, so the lever will be not always at the horizontal position. 2. If the lever is not at horizontal position, according to the lever principle, the tension is not same as the horizontal. The weight is same, but the lever position is not same. So the dropweight is not a constant pull machine. Look at the pic, 1. Left is constant pull, whether the string be elongated or not, the weight is constant, the torque is constant, the string is strung at the same constant tension. 2. Right(dropweight machine) is not constant pull, if the string elongated, the lerver will not still be at the horizontal position. The string is still be pulled - "Continuous pull", but not be pulled at the same tension-"Constant tension", according to the lever principle. I don't think constant pull is a good method for stringing. A. The constant pull is a time sensitive method. But it is not a good or easy control method for stringing. B. String is made by bundles of fibers, it's better to pull then release, and repeat that. Not only pull. Just try to hold dozens strings in two hand, then pull and realease, you will find strings are more tightly than only pull. So using the crank to pull and release then repeat again is better than only pull. To avoide the tensio lose, using pre-stretch is better. I didn't saw any electronic machine has that "Constant Pull" function key at the panel. But almost all has a "Pre-Stretch" key. For the dropweight machine, when the string lose the tension-"be elongated", you have to increase the angle between the lever and the string gripper. The pricple of the dropweight is same as a "manual crane", so if you adjust many times, the tension will be much higher than the correct tension. A weight is about several lbs, hold the weight and the string gripper to adjust the angle and have to watch the indicator carefuly, it's not easy. Crank is easy for constant pull, only release then pull again or repeat this. Of course, using a dropweight machine will be a good choice for the lower price, and it is accurate enough if you have some experience at it. Hope it is explained clearly with my poor english
i am afraid that is wrong. a electronic constant pull machine is purely constant pull. it will keep stretching the string as the string loses tension. a crank lock-out machine will stop stretching the string as soon as the desired tension is reached. so it is not constant pull. please make sure you understand the concepts and have used all these machines before you make such claims.
there are two categories of electronic machines, some are constant pull, and some are not. most of the mid->top grade electronic machine have constant pull in which they will keep stretching/elongating the string. it is true that the lower grade (no constant pull) machines are equivalent to crank. but the mid->high grade electronics constant pull machines are true constant pull and works like diagram 1 above. again, please make sure you have all the facts right first.
The lock-out will stop at the tension, yes, but the electronic machine is stop at the tension same as the crank. Then the string be elongated, the sensor in electronic machine will know this, then the moto wll pull again. For the crank, the human brain and hand will do that, release then pull again, same as electronic machine.
Didn't see the "Constant Pull" key on Yonex, wilson, babolat, gamma, Leung electronic machine panel. If you have that panel photo, could you please show me, i had search many times but didn't get it.
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.
the difference is that the electronic machine won't "stop" at that tension. it will continuous readjust "constantly". that's why it is called a electonic constant pull machine. a good machine will do that tens if not hundreds of time a second. while on a crank machine, you can only potentially do that once every 5 seconds or so. and how many times can you afford to do it?
Yes, that mean it is not accurate and not constant pull. If the elongated is no sense for dropweight, then it will be same no sense for a crank machine
no, it will stop, but the time is shortly, you should know it is pulse to control the moto. Constant pull is a time sensitive parameter, if you give crank 5 seconds, then you should give the electronic 5 seconds too and give 5 senconds to dropweight too.
in those machines, there are probably no choice to turn off constant pull. as it makes very little sense to turn it off. i have seen and used Yonex machine, seen babolat and gamma machine in action, and they will continuously adjust the stretching to keep the tension the same.
it is possible to achieve the correct tension using a crank for sure, but that's just a lot more work because you will have to keep actively cranking it. once you stop, the tension will start dropping. where as in a electronic contant pull machine or a drop weight, it will keep the tension "constant" without you doing any work. that's the machine difference.
if you want to argue that way, then nothing except dangling a weight via a pulley is constant pull. coz even an electronic machine only readjust every so many times a second and when it is not doing it, then it is not constant pull. so the argument here is really pointless.
no, it don't need to turn off the constant pull. And the concept "Constant pull" maybe a wrong concept from the dropweight. Adjust only continued in a fixed time according to the program in the chip. That mean the sensor will check the tension during that fixed time. if in that it always in same tension, then will tell the cpu it is correct tension. Then stop the moto. Whether the string lose the tension after that, the moto will didn't work again.
the motor will pull again if the tension there is any more tension loss, and it will do it forever. i have seen that happen in many electronic constant pull machines. if you see it stop adjusting, that's means that the string has stretched enough to reach a steady state. which is the stretched state that we want to see it in anyway.
No,drop weight will not keep the tension "constant". And that is the string continue losing the tension. Not mean the string continue be pulled. I had said, if you thought that "elongated" is no sense for the dropweight, it will be same no sense for crank.
a crank, after the lock out engages, will keep the length of the string constant. in that state, the string will start losing tension due to internal fibers getting stretched. the tension will be loss until you re-crank it by hand. a dropweight, will keep the tension not "constant", but by a factor of the angle, and the factor is cos(alpha), and that factor is very close to 1. so yes, it is not technically 100% constant pull, but pretty damn close to be in the noise. if you cannot understand that, again i think that this argument is pointless.
Look what you say, pull again if the tension loss. That is same as crank. right? Crank is stop, release, pull again.
i have a $500 head that will do the constant pull. probably tens of time a second. to me that's just a mid grade head. of course that also depends on your definition of mid. which i will agree to disagree.
yes. it will continuously do that. many times a second. you can only do that on a crank, one time every many seconds. sigh. this is going nowhere.
