On 2015\03\12 20:47, Recliner wrote:
Basil Jet wrote:
On 2015\03\12 14:51, Recliner wrote:
On Sun, 08 Mar 2015 21:06:13 +0000, Basil Jet
wrote:
This month's LURS meeting is about
http://www.lurs.org.uk/meetings.htm
I stopped going to LURS a few years ago when my life got too busy.
I was wondering if anyone here still goes most months?
Did you go? I thought it was a really good talk, and he answered a
lot of questions. The room was packed, too.
I did. I asked the question about why there were so many loops when
automatic unmanned trains are as happy going backwards as forwards, but
he didn't really answer.
I think I have an answer to that: the trains didn't have any on-board or
remote controllability. They just ran (forwards) when power was applied,
and stopped when it didn't. They didn't have the ability to reverse. You'd
have hd to reverse the power polarity to reverse them.
They weren't really automatic trains, more like a simple model railway. To
be able to selectively reverse them would have required some sort of remote
control, which they didn't have. It would also have been a safety risk if
the trains could run in either direction when power was applied: sooner or
later there would have been a head-on collision when two trains headed into
a neutral section from either end.
I quite like the elegant simplicity of the whole network: the trains just
ran clockwise round large ovals of variable lengths. No electronics, no
controls, no radios, no need to pass control signals between coupled
carriages. They just applied power to the motors when the third rail was
live, and slowed to a stop when it wasn't. I assume they had some sort of
simple automatic brakes that came on when the power was off, to stop them
coasting long distances in neutral sections.
Surely putting a direction switch on the underside of each train and
having a fixed lever to throw the switch in every reversing siding would
have been cheaper than digging all of these loops. And there *were*
quite a few reversing sidings in the network - how did they work? Power
off in the siding when the train goes in, bloke walks in and throws a
switch on every carriage, power on so the train can come out?
http://www.subbrit.org.uk/sb-sites/s...ck_diagram.gif