You'll probably do better by using chain drive and sprockets (like 
motorcycle chain). Wire rope
is very hard to work with, and if you pre-tension it it will simply wear 
faster.

Chain & sprocket will work best. Just have it fall into an oil pan when  
the gate if opened.

Yes, you were dreaming.

--Bob

Michiel Boerman wrote:

> I think this is normally done by using a threaded drum instead of a 
> wheel so the windings on the cable can move axially while the drum turns.
>
> Another way to get more grip could be to use two, or ever three 
> (driven) wheels in series and loop the cable through them (more or 
> less like the gear-shifter in a racing bike) . With proper placement 
> of the wheels you should be able to get 3/4 turn on each wheel.
>
> Ever consider using timing belt instead of wire rope? You can get that 
> steel-reinforced and cut to any length. A lot more expensive though.
>
> Michiel
>
>
> On 07 apr 2005, at 13:31, Lee McLaren wrote:
>
>> 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!
>
>


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