|View single post by Huw Griffiths|
|Posted: Wed Nov 17th, 2010 02:19 pm||
There is so little info on proper construction of overhead lines and street trackage. The modeling press has darn few articles - maybe once in a blue moon - and only when they decide to do a little specialty layout series.
I couldn't agree more.
The usual fare in the UK consists of occasional, very superficial, magazine articles - seemingly written on the basis that we already know what we're doing (so why the article?) - either that, or they effectively come up with a slightly more civilised way of saying "RTFM" (ditto).
This brings me to the "manual" - a Sommerfeldt "guide", which looks from the outside like a magazine - but it's very expensive and written in highly technical German, with a partial translation that serves only to confuse.
It's sometimes possible to find information on prototypes, or other scales. The Tramway & Light Railway Society website - http://www.tramwayinfo.com/ - has a section called modelling on line reference. If you go to their homepage, you're greeted by what looks like a card ticket - clicking on the flag marked modelling o-l reference, then scrolling down to the paragraph entitled general, leads you to a number of flags which lead to articles - the one about current collection makes interesting reading.
Of course, none of this tells you much about building model overhead - which is very different to the full size version. Let's face it - the distances between overhead supports are often "compressed" on model layouts - and the wire used on full size trams (and electric railways) won't always have a round profile. Also, even if the wire were the same profile, the diameter won't be exactly to scale (it would probably be too thin and snap in use).
In other words, compromises are called for - and we can only learn those from somebody who's been there before and is willing to explain. This is why I'm so glad to see this stuff appear here.
I don't want to hijack Herb's excellent "how to" thread - but one of the reasons why a number of tramway systems (especially on the European mainland) and electric railways use catenary is because trolley poles can't always be trusted to stay "on" the wires. This is particularly a problem at junctions - and led to the development of special "ears" for attaching wires and guiding poles etc through problem spots.
Basically, on systems that use catenary, cars don't have trolley poles - instead, they're fitted with pantographs (or sometimes bow collectors) which slide under the wire and are less likely to get "dewired". For this system to work properly, the wire needs to be taut - so catenary OHLE (overhead line equipment) often includes tensioning equipment (often weights on pulleys) fitted to some towers. The wire also needs to move from side to side (relative to the car and the pantograph), so it doesn't wear a hole in one spot on the pantograph head.
There's no doubt that pantograph / catenary set-ups work well (they're probably the only credible system with high speeds) - but designing them and setting them up involves a lot of skill and patience.
Saying that, trolley poles (as fitted to older tramcars - especially in the UK and USA) don't exactly have a reputation for being easy to set up. When the time comes, I'll be very interested in seeing how Herb has got them to work. In the past, I've tried and failed - judging by the number of exhibition layouts I've seen with "trolley pole style" "soft wire" OHLE and pantograph fitted cars, I don't think I'm alone.
Anyway, that's enough from me for now. I'm looking forward to seeing how this thread develops. I know it'll take time - that's fine by me. However long it takes, it means that I'm getting the chance to learn about this stuff - a chance that I haven't got elsewhere (and probably won't). Many thanks.
All the best,