On Thu, 7 Apr 2005, Lee McLaren wrote:

> I am building a electric gate and are trying to use 4mm wire rope to pull the 
> 4m gate in and out, my first attempt was a failure as I (mistakenly) thought 
> that if I cut a groove in a pulley the right width for the rope that the rope 
> would pay in and out in the same spot.
> I know how to get half a turn around the drive wheel by cutting a parallel 
> groove but would like to get three if possible so it doesn't slip.
> I am using a PIC and rotary encoder to know where the gate is so I can 
> accelerate and decelerate as quickly as possible, as the rotary encoder is on 
> the drive wheel I can only tolerate a small amount of slippage.
> 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!

One way is to put a spring made of wire of the same diameter as the 
cable on the drum and spot weld it in place. The other is to allow the 
other end of the wire to pay off into a receiver under some (weak) 
tension. The latter method will cause the drum to always have 3 turns on 
it. These will stay where they are after the device stabilises (look at 
marine winches for clues).

Peter
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