Fundamentals of Machine Elements, Third Edition
Machinery’s Handbook 29th Edition (2012)
Hy guys, it seems I don’t see all the subjects on the forum… Well I see some kind of interest in rope drive transmission.
Pierre’s guess are not that far from reality regarding lifetime. At kitewinder we have 3 bench test running 24/7/365 for ageeing kiwee. We are working on a demo video of this, will comes out within a month. What is cool is that you can multiply ageeing factor with a shorter belt. And you don’t want your test bench to be 100 meters long.
Yes, the rope contact with the pulley occurs more often as the belt is short, accelerating the ageing.
However the shorter the belt the smaller the difference of elongation between the free part and the part on the pulley, slowing ageing. The radius of the pulley should increase as the belt length and the power increase in order to avoid tension surge during the pulley passage.
Adding outdoor working conditions.
4 months? That’s not good at all. I’m looking forward to seeing your tests.
This should be balanced with
and perhaps also with
Rope manufacturers should know the lifetime in similar conditions, otherwise, test, test, test with test bench and in real conditions, perhaps using reports from kiwee’s buyers since 4 full months (if it is roughly a correct evaluation) in occasional use can take very long time.
However the shorter the belt the smaller the difference of tension between the free part and the part on the pulley, slowing ageing.
I don’t understand what you mean here Pierre.
Regarding lifetime, I just say it is a correct order of magnitude but this is for a given belt length. You might think it is a low value but regarding LCOE and the cost of replacing parts it is far from being bad. At kitewinder we made a great effort to aim a maintenance cost of 50 euros per year for kiwee one.
As the belt is longer, it is also less elongated, apart on the pulleys. The higher difference in elongation can be a factor of ageing. But it is only a supposition.
4 full months (if it is verified for “a given belt length”) it is roughly 3000 h, so a large value for an occasional use. Even for a higher scale I agree it is not too bad as a rope is not very expensive.
I dont see the connection between tension and tension difference and length of the tether?
I made this sketch to try to make things clearer.
The free part on the rope is the part which is not around the pulleys. Such a difference of the rope elongation between the stiff parts around pulleys and the slack free part of the rope is perhaps a factor of ageing.
It can be the same with a reel for yoyo systems. But I am maybe wrong.
On the following sketch and on some other messages I replace “tension” with “elongation” as it can be clearer and also perhaps more correct.
The closer the rope is to the pulley the stiffer it is, and in a progressive way, decreasing the factor of ageing. So what I try to explain with the difference of elongation for a long rope is maybe not so important.
can be righter than what I beleived in first.
I dont think you would have much wear outside the pulleys as the tension for these sections is near constant whichever length you have total. The wear should be dependent on speed/length, the radius of the pulleys and tether and difference in tension production and return side of the pulleys
The wear is not precisely outside the pulleys but occurs at rope contact with pulleys. The tension is near constant but not the elongation which is higher around the pulleys.
Sheaves do not, I think, protect the core of the rope as the rope is loaded? They also make it difficult to judge the condition of the rope so you can’t just replace the visibly damaged part.
In chaper XII, pages 177~182, goes into pulley design considerations that may be relevant here. Pages 183~190 go into groove shape.
The weight of the pulleys aloft can be a limit for the scalability of the rope-drive transmission.