Any ideas on how to change the length of an endless rope drive during flight?

I’m stumped.

All ideas welcome.

What’s a good patent search?

What would be the consequences/losses if I increased the number of wrappings around the drum at the ground station? Intuition tells me that that shouldn’t matter much? And might even be helpful as it increases the grip on the drum to (infinity)?

Sorry for the extremely bad drawing.^^
Purple is the rope. Orange rope is connecting the hubs. Change the green distance to get thrice the change in rope length. Best to do this by changing the orange rope on the ground side. Should be pretty easy.

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Thanks ^.^ That looks like the best idea possible to me. I’m thinking a problem it might have is if you only do the half wrap around the middle pulleys, the rope might slip, lowering efficiency probably, and if you do more wraps, the rope rubs on itself, wearing the rope down. So I’d want to carefully consider the design of those pulleys and see if I can get away with only the half wrap, and see how they survive when they’re being driven by a fast rope.

Any ideas on what the extra losses might be per pulley? Multiply that times two to get the total efficiency loss?

I’ll have to decide if doing this makes sense for me.

So what? No power needs to be transmitted to or from the middle pulleys. To lower rubbing of the ropes the upper orange part might be rigid and keep the upper and upper middle pulley at an 45° angle.

Don’t know about the losses. Not only friction of the pullley but also weight of the rope and drag of the moving rope are added.

Such an elonging system can be added later if the decition wether to use a rope drife doesn’t hinge on its viability.

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Oh… Then I’m tempted to just go for a very smooth/slippery cylinder for a pulley.


Strongly advise against that. Pulleys are cheap standard parts. It would even be harder to make a cylinder and the rope will slip off.

Sorry, I meant something different than what I wrote. I meant I would look for a slightly larger diameter pulley that was made out of a very slippery material, and try to see if I could make it so that it didn’t rotate, because it can’t keep up with the speed of the rope anyway.

Edit: so that would make it a plain bearing.

This doesn’t allow the length of the endless rope drive to vary between, say, 5 meters and 200 meters.

The power you can transmit through an endless rope drive depends on the difference in tension between the tight and the slack sides. I wonder how this affects that. Maybe it is a good way to control the tension so that it doesn’t get so low that slipping occurs? Maybe it increases tension on the slack side, reducing the power you can transmit?

You could also change the length of the airborne part or the height of the turbine with only one loop by having a second pulley on the ground with changeable distance to the first one.
Less airbirne weight. And one less pulley.

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Take off the pulley and insert a lightweight wheel. Put the loop of a second rope around the wheel. Reel out the second rope, when you get to the end, insert the pulley again.

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I have been thinking about that. I does increase the footprint of the base though. If you use a hook for that second pulley, you can also hook it around the rope and walk the turbine down.

I can’t figure this out. Take off the pulley from the ground station? At the end of this have you replaced the first rope drive with a second one? But that won’t work? Or do you at the end have 2 rope drives connected to each other in the air with that lightweight wheel?

Ok. that was probably a lousy explanation. Let me try again.

Say you have a loop of rope A, and the extension loop B. Two separate ropes. Initially, the rope A was connected to the geneator but you want to extend it.

First, take rope A off the generator. Instead, place a lightweight wheel (with two slots/tracks one for rope A and B). Next place rope B on the wheel also. Rope B is still on a reel. Being on the wheel, rope A and B are now synchronized and moving at the same speed.

Next, reel out rope B until the end has been reached. Place B into the generator. Start producing electricity.

You wouldnt want to do this many times due to added drag and weight of the wheel, and I guess also some added friction in the tether. But maybe one wheel and two rope lengths is feasible

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Thanks ^.^ That, two rope drives connected via pulleys, is one of the ways mentioned in the Oil Drum article I linked to. I didn’t like it that much so I kept on thinking about it. The best idea I’ve come up with I think of extending the length of the rope drive when it doesn’t need to be done dynamically, but still relatively quickly, is by linking two ropes together:

Original rope drive: ±--------------------------o

Extension: ±---------------------o

So a sliding knot on one end and a pigtail knot on the other for example.

If it is easy to run the joint through your pulleys you’ll be alright. I assumed that would not be a good solution sue to the strain on the pulleys during normal operation

Yeah. I don’t know. Maybe there are better joints that look more like you’ve spliced the rope? I saw @Kitewinder using a knot too I thought so I thought it might not be such a big issue.

Edit: an issue with a knot I’ve encountered so far is if you have more than one wrap around a pulley, you have the chance of the wrappings going over each other.

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Knot are a really complicate issue. We have a special dedicated test bench to test different knots. They have to break after the line limit strength but they also have to be really thin if you want to run them on a pulley.
What do you have in mind below that idea? I also thought about how to do this kind of things. Not easy thought

You would have a much better idea of what knots to use. Splicing the rope would be best, right? Is there a reason you’re not doing that?

I would choose a rope that had a much higher breaking strength than your maximum possible load, so that knot strength doesn’t matter. I’d also add an extra safety line, slack under normal load, under tension when the rope drive stretches too much (or breaks). I’d play with the elongation of the rope drive vs safety line so that the two are balanced and the rope drive is never allowed to have too much tension.

It seems the best option is to accept a fixed length for the tether

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Can’t do that with a kernmantle rope.

Why exactly would you want to change tether length during operations anyway?