Pulley Radius: how to factor this into calculations?

[theprgramerdude]

Would having a pulley with too small a diameter really matter in FRC-application type loads? I'm thinking of a scenario in which a high load on a tightly wrapped belt could cause it to suffer extreme fatigue and snap.

[LLogan]

Thank you very much for the input!

We are thinking of wrapping 1/8in steel cable around pulleys that are 1/2in in diameter. They need to be as small as possible to fit inside of our elevator assembly.

Our fear is that there is not enough "wrap" around the pulley, and pulling the wire around such a small diameter will be almost akin to pulling the wire across a sharp corner. I am not sure if I described this well enough....

[artdutra04]

Originally Posted by LLogan

Thank you very much for the input!

We are thinking of wrapping 1/8in steel cable around pulleys that are 1/2in in diameter. They need to be as small as possible to fit inside of our elevator assembly.

Our fear is that there is not enough "wrap" around the pulley, and pulling the wire around such a small diameter will be almost akin to pulling the wire across a sharp corner. I am not sure if I described this well enough....

What type of steel cable is it, and what is its minimum bend radius? The minimum bend radius will likely be your minimum pulley size.

[LLogan]

I don't know much about the cable other than the fact that it is 1/8inch in diameter and was taken from one of our mentors' planes.

[artdutra04]

Originally Posted by LLogan

I don't know much about the cable other than the fact that it is 1/8inch in diameter and was taken from one of our mentors' planes.

How many strands does it have? The more strands it has, the more flexible it'll be.

[Teched3]

Minimum bend radius is very important - the more strands, generally the smaller the acceptable radius. Have you investigated Spectra cord? Very flexible, light weight, and stronger than steel cable for a similar cross section. Teams have been using it for years.
Here's an EBay item number to 1/8" cord at a very good price---180614836330

[IKE]

If you must have that small of a pully, you might want to look into Spectra or other performance kite strings. You can get a roll of 450 feet for about $100. Really great stuff.