We always using "constant" as a never changed parameter.e.g. Constant Pi=3.1415926, or set some parameter as constant, Constant a=60. That mean the a is 60, and will never changed.
Maybe my english is not good to distinguish the "constant" and "continually", just thought the constant pull must be continually pulled by a constant tension, as shown in that pdf. If only continually pull, that is just pull, but don't care the pulling tension, no matter increasing or decreasing.
And pulling with a constant speed and a constant tension is better to control the elongation.
Learned from sstchur "string relax at the same rate every time", that remind me if the relax rate is same for different tension( or just assume it is same), then pulling at different tension will get different relax time. So using a constant tension and constant speed for a constant relax rate, this is easy to control the relax time. If the tension is decreasing especially cos(a) not a linar decreasing, it will be complex, not easy to control the speed or the relax time.
I think i understand the example you list. I think we are both agree if a string tensioned by a crank, then release the lock, the tension head will go toward to the racket, whether the string elongated or not, because the tension head is always pulling by the string.
I think you just thought if cut the string, the crank will not go toward the racket because of the lock. We just thought the tension head only has a lock, no spring. Actually the lock is just pulling the string. If the lock is soft as a fishing rod, holding it then cut the fishing line, the rod will swing. The lock is same too, but the swing of the lock is hard to notice.
And from the chart i drawed above, the spring is pulling, same as the gravity. Dropweight and crank are same lever system. One is tension by gravity and one is tensioned by gravity.
Only if the spring loosing to the stopper, then the lock is still pulling. If the weight arm drop to the table, then what pulling? not the table, it is the ratchet inside the gripper.
That's why i confused with that the "constant pull" only is in dropweight, not in crank.
1. dropweight not pulling at a constant tension, the tension is descreasing.
2. both dropweight and crank are always pulling the string.
3. crank is pulling at a decreasing tension too by spring or the lock,
4. from princple, they are same lever system, only the tension method is not same, and has stopper or not.
All happend on dropweight should be happened on crank too.
The different is the dropweight is easy to detect the elongation and descreased tension. but crank is not easy.
I think we thought the dropweight has "constant pull" as electronic because we saw the weight arm is still dropping by gravity. But didn't notice the tension is descreaing although the descreasing is too small maybe not noticable. And crank's head is locked, but didn't notice the spring-arm-gripper-string is still working although it is hard to notice the elongation and tension lost. The ratchet and the lock will pulling if the weight arm drop to the stopper or -90degree, or the spring stopped by stopper.
So I think we should forget the "constant pull" concept in dropweight, just let it be a electronic property "pulling string at a constant speed with a constant tension".
The string elongation could be controlled by good experience stringer for dropweight or crank. e.g. waiting a time , re-horizon, re-pull, slowly pulling or more experience i learned from here.
Constant pull is constant pull Ray! If you tension a string with a tensioning head and then cut the string while the tensioning is still active, if the head of that tensioner then move/pulls away, the machine is a constant pull. Tying a rock to a rope and dangaling it IS constant pull. Pulling on a rope through a doorway and maintaining tension on it is constant pull because if I cut that rope, you'll fall backwards because you're still pulling on it. However, if I was to close a door on that rope so that the rope is stuck in the doorjam and causes it not to move anymore when you pull it, if I cut it, you won't move because you're still supported by the tension between you/rope/door, nothing beyond the door plane of reference matters anymore, so the cut on the other side of the door doesn't affect you. In this case, the closed door variable made this example/system no longer a constant pull.
