Subject:
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Re: Reversing Loop
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Newsgroups:
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lugnet.trains
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Date:
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Fri, 13 Aug 2004 16:37:48 GMT
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Viewed:
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2481 times
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In lugnet.trains, Rick Clark wrote:
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In lugnet.trains, David Laswell wrote:
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In lugnet.trains, Larry Pieniazek wrote:
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Many of us are more interested in the trains running (remember that the
name of the group, after all, is not lugnet.electrical).
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(snip)
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Considering how little overlap there seems to be between hard-core Train
AFOLs and people with lots of electrical experience, I’d think you’d be less
dismissive of any input provided by people with electrical experience even
if they aren’t as interested in the trains as they are in the electrical
problems.
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I have to say that I am the opposite of dismissive in this case. I didn’t
follow most of what was said (electricity-wise) during this discussion. I’m a
pretty bright guy, but for some reason, electronics make my brain hurt. I’m
grateful that there are folks for whom circuitry is fun.
I think I’ve pushed the envelope as much as anyone electrically WRT LEGO
trains, but I always have to concentrate very hard to do it, and I often have
questions that are odd to answer, due to the non-overlap you mentioned. When
I go to the electronics shop and try to talk about model trains, it always
takes a lot of explaining to make them understand what I’m trying to do. And
when I go to the model train shop to try to ask about electronics, they
almost always refer me to “Bob. He’s our expert on electronics. He comes in
every third Thursday in months with an R in them.”
So anyway. Thanks for your input. As I said, I didn’t follow most of it, but
I caught enough that I’ll remember that the explanation is here if I ever
need it. (And I’ll know who to email, the next time I’m electrically
stuck...)
Rick Clark
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OK, I consider myself part of the overlap, even though I’m across the pond!
I have books on model railway wiring, as not many people can do it all in their
heads. If you are able to get international second-hand books on the net, try
“The PSL Book of Model Railway Wiring” by Cyril Freezer, published by PSL, an
imprint of Haynes publishing in the UK.
The book includes a set of 20 rules for wiring model railways, though some of
the information should be tweaked for Lego railways as we don’t have live frog
points requiring separate electrical switches.
One of the main principles is that each section of the layout should be able to
be completely isolated with all other sections powered. Therefore I suggest the
following for the reverse loop:
A: The bulk of the loop should be a station platform road (if visible) or fiddle
yard storage road (if invisible), so that stopping trains in the loop looks
natural.
B: The loop should have double isolation at each end. This can be achieved
without modification to track pieces, by using paper or insulation tape between
the contacts on both rail end contacts of a piece of track. Since it’s that
simple, there’s no need to use expensive switches.
C: The loop should have its own feed wire, which should go to a pole reverser
switch, the other side of which is connected to the controller output.
To turn the train:
1. Set the pole reverser and switch to the desired direction of travel around
the loop. 2. Drive into the loop and stop with all motors in the isolated
section. 3. Turn the controller to off.
4. Change the pole reverser and the switch.
5. Drive out of the loop using the opposite direction on the controller.
Automatic switching may be achieved with two DPDT relays if you don’t want to
stop the train (avoiding the need for A above). Connect the controller output
to the first relay’s contacts, the output of this to the straight track and the
second relay’s contacts. Connect the output of the second relay to the reverse
loop feed wire. Detect that the train has reached a certain point in the loop
(perhaps by RCX with light beam across the track, if you have one) and get the
detector to switch both relays together. If only one direction of travel around
the loop is desired, leave the switch in the position for entry to the loop, as
mentioned earlier in this thread.
To drive relays with the RCX, use 9V coil relays. Given that Lego motors are an
inductive load, I think 9V relay coils could be driven directly with no extra
components, provided the required current is 200mA or less (60mA is typical, but
divide 9V by the coil resistance to check).
At the end of the day, electrics for model railways are fun because of he
technical challenge, but they remain a means to an end. Those who do electrics
for the sake of it will lose interest once they’re done. But then it takes all
sorts of people to build a model railway.
In the MR club I go to, people specialise in trains, track, electrics, scenery,
buildings, bridges or operation. I happen to do all these things in Lego,
primarily because it’s not messy!
Clubs exist in order for people to build relationships and share ideas. We are
a resource for each other. Asking each other is often quicker than googling -
sometimes I haven’t found what I want in three hours online!
You’d think an electronics shop would have staff that understand components and
circuits, but sadly they can’t pay enough to attract electronics engineers, as
they are primarily a sales outfit. When an electronics engineer like me walks
in, they probably wonder how soon I’ll return the product for a refund, as I did
recently with a small spy camera. I had the idea of putting it in the front of
my tilting Pendolino train, with the receiver and a TV in the middle of the
layout, so the public could get a driver’s-eye view at exhibitions, and get
dizzy on the corners! It promised 25m range but only delivered 6 inches,
besides which the camera power lead got hot, indicating a short circuit, and one
of the adapters supplied was the wrong voltage. Shame other goods are not all
as good as Lego!
Until lugnet.trains.electrical exists, this seems the right place for model
railway electrics. If you want to avoid electrics, enjoy your push-along trains
:-) Otherwise I’m happy to help.
Mark Bellis
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Message is in Reply To:
 | | Re: Reversing Loop without Insulated Tracks
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| (...) (snip) (...) I have to say that I am the opposite of dismissive in this case. I didn't follow most of what was said (electricity-wise) during this discussion. I'm a pretty bright guy, but for some reason, electronics make my brain hurt. I'm (...) (20 years ago, 13-Aug-04, to lugnet.trains, FTX)
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