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> -----Original Message-----
> From: piclist-bounces@mit.edu
> Lee McLaren
> Sent: 07 April 2005 12:32
> To: pic microcontroller discussion list
> Subject: [OT] How do you wind a wire rope around a drive wheel more
> than once 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!

I'm not saying you shouldn't do it this way (I quite like the idea of
variable speed BTW, or at least soft start?), but if you do and you do get
some slippage, then where your PIC thinks the gate is and where it really is
might be different. What about when the power goes off half way through a
run?

All the comercial designs I've seen use either large micro switches or
magnetic read switches for the end stops. And they usually use chains to
transfer the drive power.

As for the answer to the question, one way to do this is to use two sets of
pulleys and wind the wire back and forth round both of them. You could
manufacture the pullys by cutting parrallel grooves in a drum, instead of a
thread.

I've attached a quick sketch of what I mean, because reading this back
myself, it doesn't make much sense!!

Cheers, and good luck...Mike.



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