Re: Need speed switch for DIY funicular/hillside elevator

["Doug" <not@xxxxxxxx>]

Since the brakes will be on the car, its the weight of the car "pulling
against" the cable that will hold the brakes off, it doesn't matter if the
cable is sagging in the middle, its still holding the car and the brakes
will be held off.

It could be as simple as the cable passing through a correctly rated coil
spring at the car and attached to a lever that will hold off the brake, when
the cable is attached to the spools and the spools are winding or unwinding
normally the weight of  the car will compress the spring and  release the
brake, if the spools are unwinding  uncontrollably  or the cable is broken
then there will be nothing for the car to "pull against" and the spring
would expand and the brakes will no longer be held off.


Doug

<astutesolutions@xxxxxxxxxxxxx> wrote in message
news:1162217574.700283.236550@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>>
>> Elevators often have a brake that is held off by the cable tension where
>> it attaches to the cab.  you can do the same thing, the cable attachment
>> holds open a brake that would grab the rails.  If the cable breaks or
>> loses all tension the brakes grab.  Even if the cable slacks, there
>> should still be tension at the cart attachment point.  This is totally
>> automatic, no user input.
>>
>> --
>> Free men own guns - www.geocities/CapitolHill/5357/
>
> Nick, I undestand what you are saying.  I suppose you just have to be
> there to see it, but the cable is quarter inch aircraft cable and is
> pretty stiff.  It is long too, over 150 feet.  When that cart goes down
> in a freespool condition (drums rotating freely) it will be dragging
> that cable down with it.  As it drags it down there is going to be some
> tension there because the drums/spools have some inherent resistance
> until they build up speed.  Even when the cart goes down, the cable
> sags in between the supports some.  I guess what I'm trying to say is
> that I don't know an easy way to indicate that tension drop.
>
> In the event that both the cables snap, this would work beautifully,
> but both would have to break at the same time, and each one is rated
> for about 7,000 lbs.  Thanks!
>