Breaking Cable

[Bcahn836]

we got some steel cable that one of our mentors uses for his prosthetic arms. He has a 2000 ft roll of it and let us use about 20 ft of it. However we didn't use it to hang from the bar but to open and close our arm to grab the 2X ball, and we havn't broken it yet. He claims that he has broken the pieces on his arms lifting an extreme amount.

[BillyGoats]

he have used cable for the past three years

2002 - held our claw... we broke this a lot....
http://www.valleytech.k12.ma.us/robo...002%20Claw.jpg

2003 - push pull system for out arms.. never broke it never became tagled! great stuff
http://www.valleytech.k12.ma.us/robo...botonField.JPG

2004 - holds us up...
starts - http://www.valleytech.k12.ma.us/robo...UCFReg3300.JPG
on bar - http://www.valleytech.k12.ma.us/robo...UCFReg5400.JPG
can hang this high - http://www.valleytech.k12.ma.us/robo..._UCFReg112.jpg

we had held our self plus another robot many times! great stuff!

I appreciate all of the comments. What I'm really wondering is, why does cable (spectra, fishing cable, etc.) quote a test strength in pounds, rather than foot-pounds? Obviously the same weight bouncing on the cable will break it easier than a static load. And it's the dynamic breaking strength that I'm really interested in.

In our tests, we also noticed that the cable tended to break where it was tied to something else.

[Bcahn836]

I think it all depends on how the cable is tested and rated. Like you said it might hold a certain weight still but not bouncing. In our test we stretched some nylon cable across a jig we made and but weights on it. The cable was rated at 150 lbs but broke at 60 lbs. So as i mentioned before we used some steel cable that we haven't been able to break so far. I think the motors would go before the cable. LOL