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In lugnet.technic, Steven Lane writes:
> Ok, here's my idea for a solution for a vertically lifting bridge.
>
> All you need is one winch connected to one lifting line. You also need one
> control line(running off the same motor but geared down 2:1).
>
> The lifting line goes up the first tower down to the lift span, turns 90
> degree's around a free running pulley, across the span, round another pulley
> and up the other span where it goes over two more pulleys and then goes back
> to the winch via a mirror image route back to a second winch drum on the
> same winch axle.
>
> This is where you lot say it'll just pull from one side and jam. This is
> true except that their is a control wire connected to the underside of the
> span at the end nearest the winch. The control wire also goes to the lift
> span across two pulleys and back to a second drum on the same control wire
> winch axle.
>
> The bridge rises at speed X, the main winch pulls in the line at twice x and
> the control wire is paid out also at speed x.
>
> Therefore as the 'controlled' end of the span cannot lift at a speed greater
> than x the span has to stay level. And as the lines are pulling on the 4 top
> corners the span should stay level in both the x and y plains.
>
> You would of course need a mechanism to tension the control wire correctly.
>
> Steve
I've thought of a simpler way of describing my system.
Basically you have a rope stretched between two towers. If you pull the rope
the span goes up, release it and the span goes down. The wire is connected
to the lift span at both ends via pulleys and the wire is pulled from just
one end. Because this would proabaly cause the span to lift higher at the
end closest to the winch a control wire also geared to the winch holds that
end down. Because the control wire pulls down(paying out as the bridge
lifts) opposite to the main wire pulling up, the system would remain level.
Steve
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Message has 1 Reply:
 | | Vertical lift spans (was: Re: drawbridge
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| Not sure where to chime in, so I'll jump in here. Regarding the lifting of vertical lift spans: I've built many of these over the years and my latest version (yet to be published on the internet) takes advantage of an engineering survey done on one (...) (22 years ago, 30-Apr-03, to lugnet.technic, lugnet.trains)
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Message is in Reply To:
| | Re: drawbridge
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| (...) Ok, here's my idea for a solution for a vertically lifting bridge. All you need is one winch connected to one lifting line. You also need one control line(running off the same motor but geared down 2:1). The lifting line goes up the first (...) (22 years ago, 29-Apr-03, to lugnet.technic, lugnet.trains)
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