faklord wrote:Well....I'm sorry to dissapoint.... It isn't quite a magic as I thought.
I have done a bit more tinkering.
Built a system with low friction ball race pulleys.
Now it behaves exactly how I originally suspected.
ie Put tension on bottom pulley and middle pulley (or ring in the diagram) shoots up to collide with the top pulley (ie system goes to its maximum length).
It seems that the system I previously built with rings just relied on friction. Obviously, it can be made to work (Zeeko made it work) but it isn't the magically stable sytem that I thought it was.
I am impressed with your experiments...first with the elastic and then with the low friction pulleys. Nice job. I wish I had some pulleys like that...ceramic? Where can I get some?
I guess that answers the question of how the Zeeko system was created. It must have been by trial and error to determine that it would work with the kind of forces generated by kiters and kites. If he drew a force diagram, he probably would have concluded that the system would not work. I do believe that there is a lot of friction in the system, using 3 rings. My present experiment uses 3 old pulleys from a kite bridle and a windsurfing downhaul hook, and I have been impressed by the range of readings I have been getting, due to "sticktion" (getting the pulleys to initially turn). The forces that I have been recording show a decrease in force of a couple pounds, once the pulleys start turning. I may try to calculate the force of friction of each pulley (or better yet of the rings, that I will actually be using, in my set-up) by measureing the tension of each leg on both sides of the pulley, while the system is under load. I have been using 40 pounds of force on the system... but 40 pounds of force is not much compared to the hundreds of pounds of force that a kiter will actually apply to the system...but my fish scale only goes up to 50 pounds.
So, a preliminary conclusion, as to why the total length of the system does not shorten in kiteboarding application practice, would be that: as the kiter and kite start to exert "extreme" force on the system...the friction on the rings and pulley also becomes more "extreme", and resists the natural movement of the system to acheive neutral stability, where the 2 top rings would be drawn together.
So, I guess we may need clarification of the force diagram, showing unbalanced forces.
Very interesting. I wonder what would break or slide first with the Zeeko set-up, if the system was taken to failure?...I bet this could be done with a manual 3 ton "come-along" hand winch.
It will be fun to find out what real-life kiteing situation will exert enough force on the system to cause the system to either break some component... or will cause the ring to slip and thereby, cause the total line length to elongate.
I would guess that this Zeeko system will be popular, and will get some real Beta Testing, by kiters... just like Microsoft products. I will be one of those test crash dummies.