cable for gripper

My robot has a gripper with a a highly geared little 2 watt motor that turns a shaft, winding up a string, which pulls the two jaws together. There is a spring for retracting
the jaws.
It all works okay, but the limiting factor on the gripping power is the string. When picking up something fairly heavy, the string will break. So I need a stronger string or cable. I am currently using a braided nylon string about 1.2mm (1/20 inch) thick. I cannot use steel cable because the winding shaft is only 1/8", and steel cable won't bend that tight (I tried).
I need something flexible, but with as much tensile strength as possible. I only need about six inches. So what should I use? What about kevlar cord? Anyone know where I can get that?
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Polyfilament fishing line. Go to a sporting goods shop and get a short sample. It might be free.
Cheers!
Sir Charles W. Shults III, K. B. B. Xenotech Research 321-206-1840
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Bob wrote:

1. Piano wire 2. Some brands of high quality fiber optic cables are lined with kevlar.
J
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I wrote:

Sir Charles W. Shults III, K. B. B. wrote ...

Thanks for the suggestions. But I ended up buying some 240# Kevlar cord on E-Bay. But now I have another problem: how do I keep Kevlar cord from unbraiding? With Nylon, I just melt the end with a cigarrette lighter. But Kevlar doesn't melt - it burns. Tying a knot doesn't work, because I need to thread the cord through the gripper mechanism, and a knotted end won't fit. The ends unbraid while I am threading it, and then get stuck. The best idea I could come up with was dipping the ends in melted wax. But the wax flakes off, so that is only a temporary solution.
Once I thread the cord through the gripper, I tie a knot at each end to hold it in place. But that is another problem. Kevlar is "slippery", so the knots tend to come loose.
If anyone knows of any tricks for working with this stuff, please let me know.
-bob
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Bob wrote:

Kevlar is usually secured with a friction grip with smooth surfaces. The stronger it pulls the tighter the grip. You may have to make a mechanism like that or buy something that someone already makes. Some fiber optic connectors have this mechanism, and you may be able to cut it out and use it.
J
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