Subject:
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Re: Train engine transmission
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Newsgroups:
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lugnet.trains
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Date:
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Wed, 1 Mar 2000 19:55:25 GMT
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Viewed:
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1142 times
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In lugnet.trains, Frank Filz writes:
> Fredrik Glöckner wrote:
> >
> > (This article is about the mechanics of train engines, not necessarily
> > related to the LEGO train line. I hope to learn what I need to know
> > if I'm going to build a train engine in LEGO some day, though, so I
> > hope this is enough to justify posting the article here.)
>
> I can't answer everything here, but will spit out some information...
>
> The rod coupling works very well with steam engines for the reasons you
> surmised. The flexing issues due to curves and bumps are almost nil.
> This is not the case in temporary logging and mining lines which is why
> the various types of geared locomotives (Shay, Heisler, Climax, and
> others) were invented, though the Heisler rod couples the two axles in
> each truck (bogie).
>
> I'm not as familiar with Diesel etc. locomotives, but I would guess that
> only one axle is driven by the motor when rod coupling is used.
Yes, there are several examples of Diesel-mechanical shunters (US=switchers)
on which the only powered axle has no whells at all but is simple linked to
the drive wheels via these rods
Modern
> locomotives (which are not Diesel for the most part, they are usually
> turbines, if you stand next to one as it winds up, and don't realize
> that they use turbines, you may start looking for the airplane...) which
> are not totally electric are actually still driven with electric motors.
> The Diesel or turbine drives a generator which then runs electric motors
> which are usually on every axle.
You also see Diesel-Electric shunters with coupling rods, but the only obvious
reason for this is to prevent individual wheel-slip if all axles are powered
individually
>
> An interesting note about differentials is that they were tried in the
> early days of the geared locomotives, but it was discovered that they
> completely lost power in curves, making them absolutely useless.
>
> One place where you can really hear the results of the fact that
> differentials are not used in trains is on subway lines, especially in
> the Park Street station on the Boston MBTA. There is a reversing loop
> there which can't be much more than a 100 foot radius curve, and boy do
> the trains squeal going around it.
>
> --
> Frank Filz
I think the sound you are referring to is known as 'flange squeal' and is
probably more to do with the angle that the outer flange meets the rail when
the centrifugal forces push the train towards the tangent (boy, this is
getting heavy!), If you examine the profile of a train wheel you will notice a
banked tyre, only a degree or two, with a rolling profile towards the flange.
This allows the outer wheel, when pushed against the outer rail, to rise up to
a slightly larger diameter and the inner wheel to drop to a slightly smaller
diameter. The transistion is generally helped by the profile of the rail edge
itself which is slightly rounded (and well worn in tight curves!). The effect
of these different diameters works in a similar way to a differential and
allows the outer wheel, using the larger effective diameter, to cover a longer
distance than the inner wheel. Of course, with a radius down to 100ft this
probably doesn't work at it's best (Phew, I need a beer!)
Now build THAT out of lego!
Jon
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Message is in Reply To:
 | | Re: Train engine transmission
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| (...) I can't answer everything here, but will spit out some information... The rod coupling works very well with steam engines for the reasons you surmised. The flexing issues due to curves and bumps are almost nil. This is not the case in (...) (25 years ago, 1-Mar-00, to lugnet.trains)
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