>I have spent hours on the net trying to find the answer but don't seem
>to have hit on the magic search terms, I am sure I have seen this done
>with some sort of thread on the drive drum but might be dreaming it!

Normally there is some form of concave shape like on the windlass of a boat.
The rope winds on one side and works its way down the slope and up the other
side as the windlass turns.
See this picture http://www.c-mesales.com/contents/media/powerwinch_26.jpg

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist