Pulleys and Rope for elevator systems

We assumed we would use either 550 cord or 1050lb 3mm Braided Spectra
(https://www.amazon.com/Spearit-100FT-3MM-SPECTRA-BRAID/dp/B004L234TW/ref=sr_1_4?ie=UTF8&qid=1547562790&sr=8-4&keywords=spectra+line)

I would like your input on pulleys and other line options. We are building a two stage elevator using the Andymark 1x2 kits and will be counterbalancing the first stage using 2 constant force springs.

Stay away from 550. Parachute cord is nice for some things: its fairly smooth outer cover and its high elasticity make it good for things like parachutes. You really aren’t looking for a stretchy rope for an elevator. It’s not the correct application.

Most teams just whip up hdpe or delrin rollers on a lathe because they are cheap and effective. We’ve always gone the more pricey route of sailing pulleys, primarily because I usually have them handy.

Whichever you use, keep in mind that the most common pulley failure is when the rope run manages to jump the pulley and wedge between the pulley and the side piece. Don’t leave much tolerance between the sides of your pulley and support bracket. And don’t use a spectra line that is so thin that it can fit into the gap.

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+1 for making sure the rope you choose can not jump the pulley. 550 does this very easily. Last year we switch to a 3/8 braided rope for our elevator and it was a huge improvement, after the 550 gave us a ton of issues.

1/8" Amsteel marine rope is what we used last year. This stuff is light weight and super strong.

The Spectra line you linked to is made of 3mm UHMWPE, which is pretty commonly used for elevators. It’s insanely strong stuff.

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I’ll 2nd the 1/8" Amsteel. Used it for climber last year and never had an issue with it.

I’ll 3rd the amsteel along with many other top tier teams, it has an insanely small stretch factor unlike spectra line which you will have to tension more, and it’s stronger. its what 973, 2471, 254, and a few others use.

Amsteel is a product name that Samson uses to describe their lines made of Dyneema. Dyneema is actually very similar to Spectra and both are UHMWPE (ultra high molecular weight polyethylene). Dyneema is a product from a Dutch firm whereas Spectra is made by Honeywell. I’m not sure what you mean by stretch factor, but Spectra actually has a lower elongation than Dyneema. In practical terms we’re talking about single digit percentages that no FRC team will every notice - especially over a short length like a lift or a climber.

Each manufacturer tends to use a slightly different technique, they may weave the ropes differently, or use different coatings in their process depending on the application, or add an anti-chafe cover, or make the line ‘hollow’ so that it is easier to splice.

On an FRC robot, Spectra and Dyneema will be nearly indistinguishable from each other. Either will be significantly stronger than 550 cord for a given diameter. And now I’m done nerding out about that topic.

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We got away with 1.7mm Spectra for our lift cable last year. We even used it to climb.

Spectra/Dyneema are the miracle material that every team needs, but they don’t realize it until they use it for one season. The stuff is amazing.

OK 550 OUT - Spectra and Dyneema IN. Anyone have any good leads on pulley’s?

I posted a link above. Harken makes excellent pulleys with delrin roller bearings, but for FRC they are expensive. Is there a specific configuration of pulley you’re looking for? Here’s a nice graphic showing some of the different styles.

http://glenmoresailboats.com/wp/wp-content/uploads/2013/10/harken_micro_block_detail_page2.jpg

You can see how easy they’d be to make using bent aluminum plate and a delrin roller. I’d suggest that before dropping the money on theirs. If you can’t easily make the sheaves, then I’d suggest a place like zoro:

https://www.zoro.com/ronstan-sheave-fibrous-rope-sheave-od-34-in-rf1743/i/G3475561/

We must have had a different type of spectra cable, in 2015 we used spectra on the lift and had lots of problems with stretching ¯\__(ツ)_/¯

The material has very little stretch. Is it possible your knots were slipping? These kinds of cables are slick and don’t hold knots as well as typical rope you might use. There are clever ways to splice the ends to make for a very solid non-slipping connection however.

That amsteel marine rope is excellent. In 2017 we used it with no issue for our climb.
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Last year for our elevator we used cable which I would not do again. I would run this type of rope as it’s muuuuch easier to work with.

My teams experiences were the same. There was some intial stretching with a new length of cable but after a few runs up and down it’s stopped. It was great stuff and it lifted 2 robots last year all season long with no problem.