Breaking Cable

[ChrisH]

Originally Posted by WebWader125

To make sure this was adequate, we used the line to lift a student who weighed over 200 pounds. Lifting was no problem, but a little bouncing would break the line. Just to be safe, we decided to go with the 876-pound test cable instead. Since an active competition might involve more than just lifting dead weight, I'm wondering if there's a good way to calculate the correct cable size, rather than just testing it like we did...

Generally static loads, those that do not change with time (like a hanging robot), are much easier to calculate than dynamic loads, that do change with time (like a bouncing robot). Impacts and bouncing are among the hardest to determine.

Often a simple test such as you conducted is the quickest and easiest method for determining how to handle a dynamic load. Another method is to take the static load and use a safety factor of 4. That will generally cover FIRST robots for all but the most severe dynamic effects. That's what I do and I haven't had anything break yet.

BTW kudos for testing the bouncing condition. Most people wouldn't even think about "bounce", let alone test it. At least not until after something broke.