A good solution is to mount your rope spool on a thread with a thread
pitch = to your wire width. then the spool will move up and down at the
same rate as your wire "eats it up".

A second best idea is to use a deep grooved pulley/spool, and actually
allow the wire to wrap multiple turns on top of itself. This of course
results in non-linear rate of pull of the cable, but that probably does
not matter for a gate.

jon 

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Lee McLaren
> Sent: 07 April 2005 13:32
> To: pic microcontroller discussion list
> Subject: [OT] How do you wind a wire rope around a drive 
> wheel more thanonce and not have it travel up the wheel?
> 
> Hi,
> 
> 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!
> 
> regards
> 
> Lee McLaren
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