What are your tips and tricks for making sure rope doesn’t bind up when getting spun on a spool? I’ve noticed that rope sometime pulled so tight it wedges itself in between other pieces of rope.
What kind of rope are you using, we never have this issue with uhwmpe (both wcp stuff and true amsteel).
Typically you want a nice wide spool with a somewhat optimal Fleet angle. But our spool was incredibly thin this year with rope spooling on itself 2-3 times and we never saw any issues.
If there’s enough packaging space a grooved spool with a fairly small fleet angle will cleanly wrap only a single layer of rope which won’t allow the rope to bind on itself.
I have typically used a piece of 1/2 inch hex shaft long enough so that the cord forms only one layer. I use an attachment point that is offset from the path of the cord so it encourages it to wind on in a spiral pattern.
I have seen what you described when the cord formed multiple layers.
When I have seen multiple layers not do what you describe, it was something incompressible like wire-rope and there was some mechanism for making it form neat layers with no gaps.
I like to use 1" wide flat webbing instead of rope for this very reason.
Does anyone have any experience using fishing line for this purpose? It seems like it would be a great choice for elevators but I don’t think it is very popular in FRC at all. Braided fishing line can be very strong (100lbs or more), very thin (something like 0.03” diameter), very light, very inexpensive, and is designed to be spooled and unspooled quickly. Something like this: https://www.amazon.com/RUNCL-Material-Multiple-Freshwater-Saltwater/dp/B073TTRM1C/ .
Does anyone have any experience using fishing line like to is as rigging for an elevator?
It would need to handle 150 lbf, PLUS the resulting dynamic loading. Also, the knots can be… more complicated than people are used to.
Don’t get me wrong, it’s not a bad thinking, but you need to be able to handle the load both in the line and the knots.
Based on the listing it just looks like really thin UHMWPE which is what is usually used for rope in FRC but in larger diameters to handle higher loads. Typically 7/64ths or 1/8th UHMWPE is used when climbing which has an ultimate tensile strength in excess of 1500lbs, while smaller diameters such as 1/16ths can be carefully used for lower-load applications.
Materials from the marine/fishing/kite flying hobbies are a good source for strong lines. Spectra and Dyneema are name brands that are high quality. A 550 lb line is strong enough to lift an FRC robot and super thin. There is not really a concern for the line overlapping or bundling up if you have a small line and a large spool:
If there is binding in your elevator, or your programmers don’t tell the motors to stop, you can snap lines that are that small, so beware!
Knots are hard to deal with in this kind of line too, it’s pretty slick. With small lines, you can superglue the knot to keep it set. With larger diameter lines, you can use some clever tying techniques to keep them from coming apart, Like so.
I don’t have any experienced with the grooved pulleys that some teams have used, but they do look pretty slick (2471 here):
I can confirm that a threaded spool is super nice, we never had any binding or tangling problems. However machinability can be a limitation of this design. We were lucky enough to be able to machine it on a four axis mill at our local community college.
Does it stretch? If it stretches than it’s a non-starter. This is why Dyneema is amazing, after the intitial tensioning it barely stretches. Our 2018 elevator is still perfectly tensioned.
If you want to see how that works, enter “levelwind” into your favorite search engine.
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