QUOTE (Richard Johnson @ 16 Dec 2008, 08:06)
<{POST_SNAPBACK}>***No, it is theoretically possible to do it (and it
is done on trolley and electric only layouts) but its advised against because:
(1) Operating catenary HAS to be way overscale to take the load of the model pans and unlike with DC there is absoutely no operating advantage in doing so, so why would you bother
That is true if you use the pantographs straight out of the box, even Sommerfeldt ones, the spring pressure is quite considerable. However my club, Nottingham MRS, has two layouts Deepcar and Carstairs, which have scratch built catenary and the catenary wires are much finer than proprietary ones, as you can see in the links to pictures on our web site of Deepcar:
http://www.nottingham-modelrailway.org.uk/dbl76.jpg and
http://www.nottingham-modelrailway.org.uk/tommystn.jpg and of Carstairs
http://www.nottingham-modelrailway.org.uk/carstpics.htm All our OHL locos run with the pantographs up, but
with the spring pressure much reduced so that the pans don't push up the catenary wire or bend the masts as they pass below.
The catenary is wired in to the common return but the pantograph locos do not depend on it as the catenary doesn't extend into the fiddle yards. It did once but got in the way, and was taken down.
As to why would you do it, well why not? We always try to emulate the prototype don't we. After all electric traction is more prototypically correct than steam, unless it's live steam, or diesel.
If you want to see Deepcar, it will be at our show in Nottingham in March next year, see our web site for details
http://www.nottingham-modelrailway.org.uk
QUOTE (Richard Johnson @ 16 Dec 2008, 08:06)
<{POST_SNAPBACK}>and
(2) as you surmised, if you use catenary for the power pickup on DCC, you lose all the directional flexibility of operation DCC gives as reversing loops/any reverse capable trackage like Wyes would become a no-no .....and the loco's could only ever be placed on the track one way (ie the electric locos would all need 100% consistency in wiring and then in being placed on the track ....or a short will happen).
All you need to regain the operational flexibility is automatic switching within the loco of the return path to the track from the left to right side of the loco, or vice versa. I suspect that an electronic circuit to do that could be built with rapid switching to avoid shorting, but I'm no electronics whizz, but I did devise a theoretical circuit to do it with relays, but space inside the loco would be a problem, and I suspect the relays wouldn't act fast enough to avoid a short. Hence the need for electronics, but there's little enough space inside a loco as it is. However the problem wouldn't arise if your layout didn't have any Ys or return loops, or you bonded both running rails together so it didn't matter which way round the loco was facing. Only snag with the second option is that you could only run OHL locos unless you had Maerklin stud contact track and used that in lieu of the catenary for non OHL locos. Where there's a will there's a way, even it its only to cause excessive complication.
Keith.