> on the rope). The groove in the pully may actually need to be a sharpe V shape
> two or three times as deep as the diameter of the rope.

Not really.

Have you ever looked at the drums used on garage doors?
http://www.channel3000.com/exterior/1140134/detail.html
  photo14 link
The groove is the diameter of the cable, round and the depth
is half the cable thickness. They seem to work just fine in
millions of installations.

For the OP method to work, he needs to loop the cable
back onto the drum, and have a stiff tension spring to
prevent the cable from coming slack as the gate bounces
along.

Robert
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