Subject:
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Re: Articulation with "working" connecting rods
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Newsgroups:
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lugnet.trains
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Date:
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Mon, 4 Sep 2006 21:44:30 GMT
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Viewed:
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2507 times
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In lugnet.trains, Sebastian Dyson wrote:
> I'm trying to design an 8-wide 4-8-4 using Big Ben's wheels (CAD only, I'm but a
> poor student), and want the loco to be able to negotiate standard Lego curves.
> As the leading truck has an axle each side of the cylinders, I'm finding it hard
> to keep the cylinders fixed relative to the driving wheels without the cylinders
> and/or rods fouling the wheels of the pilot truck.
>
> I could raise the cylinders, as in Rosco's X class
> (http://www.br-eng.info/about/lego/mocs/x-class.htm), but I'd really prefer not
> to, as the prototype's cylinders are quite low (the bottom edge of the cylinder
> is about level with the leading truck's axles), and I can only move them so far
> outboard before they look ridiculous.
>
> Another option is to have no connection between the rods on the wheels and the
> cylinders and have the cylinders turn with the leading truck, which seems a
> little like cheating.
>
> So if anyone's got any tips or experience in this, I'd love to hear it.
Not sure I can help you much here - I designed my cylinders to be quite flat so
they could slide 'twixt motor and soleplate. With small BBB wheels on the front
your front truck is lower than a standard motor, but if you say Rosco's are too
high for you then my stuff is no good.
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=92701
http://www.brickshelf.com/cgi-bin/gallery.cgi?f=93959
Everyone's prototypes have the cylinders level with the axles, as that's the
most efficient way to do a power stroke. No-one seems to have cracked it yet
though with a wheelbase flexible enough to handle Lego curves.
Mark Bellis has done some tests using flex system so that the rods can bend and
change length. But, you need a long large-scale wheelbase to get enough
flexibility - both in terms of the lengths of tube for a telescoping action and
to get any lateral flexibility . Even then you get a lot of binding in corners
and you don't get great reliability.
Another way would be to use ball-joints on the main drive rod, so they can flex
sideways. But then you're increasing the width quite a bit.
Jason R
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Message is in Reply To:
 | | Articulation with "working" connecting rods
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| I'm trying to design an 8-wide 4-8-4 using Big Ben's wheels (CAD only, I'm but a poor student), and want the loco to be able to negotiate standard Lego curves. As the leading truck has an axle each side of the cylinders, I'm finding it hard to keep (...) (18 years ago, 4-Sep-06, to lugnet.trains)
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