Eastwood Town - A tribute to Gordon's modelling.

[G.M.R.]

I have a very similar set up, Martin, using LEDs to indicate turnout settings by wiring them between frogs and one DCC rail.

 

I think that if you just included a short length of isolated rail - couple of centimetres long - and connected that to the other side of the LED/resistor you don't need the bent piece of metal. the first loco wheel will connect the short isolated section to power, and the LED will illuminate.

[martin_wynne]

I think that if you just included a short length of isolated rail - couple of centimetres long - and connected that to the other side of the LED/resistor you don't need the bent piece of metal. the first loco wheel will connect the short isolated section to power, and the LED will illuminate.

 

Hi Geoff,

 

Yes, that will work most of the time. However, if you have a 4-wheel rigid-wheelbase loco or unit (an industrial shunter, or pacer railbus, say), it will be mostly picking up on one wheel only on one-side. So it may stop and get stuck on the isolated section. I don't suppose Gordon will be running such trains down the ECML, but other RMweb members do run such models.

 

The springy contact detects all (metal) wheels, whether they are picking up or not, and doesn't interrupt traction power. It can be installed in finished working track, and moved to a new position if needed.

 

regards,

 

Martin.

[aardvark]

I'm a beginner, but it seems to me that Gordon could power his Tortoises with a single DC supply through DPDT switches. I must be missing something. Perhaps the cost of the DPDT switches and the extra wire to each Tortoise outweighs the cost of the second supply?

Edited January 21, 2016 by aardvark

[gordon s]

There is some merit in what you say Aardvark, but the cost of a simple power supply from RS is less than a tenner from memory and it does reduce the wiring from the panel to the Tortoise motor from two wires to one.  

 

No big deal you may think, but when you are building a large layout with 15 or so baseboards and you want to be able to dismantle it, the number of additional solder joints is considerable.  In my case ET won't leave home, but I am building it in a way that it can be dismantled.  If I were exhibiting, then 15 boards would require an additional 15 lengths of wire and 30 solder joints, so having two power supplies is so much more convenient.  Having just the one wire to the Tortoise simplifies the whole issue and connection to the +12v and -12v bus supply only requires very short jumper leads from the bus wires.

 

I don't know if this is an issue or not, but my 12v bus to power point motors has a run of 30' in each direction from the central control point.  I use 1.5mm copper for this bus, the same as the DCC bus wires.  The link from the bus to the motors is in 16/0.2mm.

[chris p bacon]

All of my secondary power circuits come from a pair of 12v power supplies wired to give 12v/0v/12v.  These are used to run all my Tortoise motors using just one wire to activate the switching.  That 12v/0v/12v supply would also run lighting etc if needed.

 

There are no section breaks in DCC unless you want Power Districts.  I will split ET into three power districts.  The lower level storage, the continuous loops and ET terminus itself.  Both rails are broken to give completely independent power districts and each district has it's own bus wiring (from memory).

 

Edit: Tortoise wiring diagram

 

Screen Shot 2016-01-20 at 18.16.31.png

 

 

There is some merit in what you say Aardvark, but the cost of a simple power supply from RS is less than a tenner from memory and it does reduce the wiring from the panel to the Tortoise motor from two wires to one.  

 

No big deal you may think, but when you are building a large layout with 15 or so baseboards and you want to be able to dismantle it, the number of additional solder joints is considerable.  In my case ET won't leave home, but I am building it in a way that it can be dismantled.  If I were exhibiting, then 15 boards would require an additional 15 lengths of wire and 30 solder joints, so having two power supplies is so much more convenient.  Having just the one wire to the Tortoise simplifies the whole issue and connection to the +12v and -12v bus supply only requires very short jumper leads from the bus wires.

 

I don't know if this is an issue or not, but my 12v bus to power point motors has a run of 30' in each direction from the central control point.  I use 1.5mm copper for this bus, the same as the DCC bus wires.  The link from the bus to the motors is in 16/0.2mm.

I will admit to being a bit thick where electickery is concerned but I don't understand how you connect the + and- to create one bus? or does the digram not show there are 2 seperate wires?

 

Edit -  I think I've just worked it out..........sometimes I get there....

Edited January 21, 2016 by chris p bacon

[gordon s]

I'm not either, Dave, but I run a single bus wire in 1.5mm green conduit cable.  That is my 0v line.  Each Tortoise has a short link to that bus wire.  From each switch on the control panel then all you need is a single wire (I use 16/02mm) to run from the switch to the other power connection on the Tortoise.  Throwing the switch then supplies either +12v or -12v to the motor and reverses the throw.

[gordon s]

Right, a change of subject.  I've been working on ET boards all day and have now reached the point on the layout where the skew bridge will sit.  Here's a pic looking down from above showing the double track above and the single line below.  Rather than have a simple straight line across, the lower line is in an S shape.

 

 

Mt thoughts are to cut away the 12mm ply on the top layer and build up the bridge supports within 6mm of the top surface.  I will then build the bridge track bed in 6mm MDF and lay that on top of the supports such that it is flush with the upper trackbed.

 

It's at this point that I need some clarification as I would hate to cut the upper board incorrectly as it is all in one piece covering the lower level diverging lines..  

 

The bridge itself crosses at roughly 25-30 degrees, so I'm assuming the bridge is in the shape of a parallelogram.  What I'm not sure about is the width of this bridge with it's plate girder sides and centre plate.

 

The supports will be built in wood/plastic card to represent stone supports.  Would these be curved to follow the track bed shape or would it be normal practice for them to be straight following the parallelogram shape of the bridge?

 

If straight would they be set some way back from the lower track line or would they be quite close to the line of the track using the minimum clearance? 

 

Thanks for any guidance you can offer.

[martin_wynne]

What I'm not sure about is the width of this bridge with it's plate girder sides and centre plate.

 

The supports will be built in wood/plastic card to represent stone supports.  Would these be curved to follow the track bed shape or would it be normal practice for them to be straight following the parallelogram shape of the bridge?

 

If straight would they be set some way back from the lower track line or would they be quite close to the line of the track using the minimum clearance? 

 

Thanks for any guidance you can offer.

 

Hi Gordon,

 

Here is my bridge scheme again:

 

 

The abutment walls below the bridge deck would be straight with angled ends. They will be as close to the track as a full structure clearance allows -- test it with the dummy vehicle in Templot. The minimum structure clearance for a single track is 15ft-4in wide (61.33mm in 4mm/ft scale). Set the clearance envelope on the dummy vehicle accordingly.

 

regards,

 

Martin.

[The Stationmaster]

Gordon looking at a couple of examples (Cogload and Battledown) confirms my impression that the walls are normally straight although the abutments can be at an angled and this makes sense when you think of brick or dressed stone walls.  Things are possiby different with modern concrete structures but the flyovers at Airport Jcn on the GWML seem to have straight site cast concrete wing walls.

 

So the basic parallelogram shape would apply as far as I'm concerned.  The wing walls would have to be compliant with structure gauge as an absolute minimum and the application of the permitted minim a on each side would set the distance between the parallel walls - which is quite considerable at both Cogload and Battledown because of the curvature in the double line passing underneath the single line viaduct part of the structure.  The distance between the wing walls at Aynho Junction flyover is even greater due to triple track passing underneath the flyover although the curvature is not as marked as at the other two I have mention.

 

The only type of girder work arrangement I have seen for the flyover part has the sides set paralel to each other with the connecting girders between them set at a right angle to the sides.  How you decide to set your 'flying over' track will also have an impact but as it is curved I would suggest going for a fully ballasted line and not the longitudinal timbered arrangement used on some girder built viaducts.  

 

PS Both Walnut Tree and Pwll-Y-Pant (Llanbradach) viaducts on the Barry Railway, later GWR had ballasted track beds and Walnut tree was built on a curve although the girder sections between piers were a series of straights carrying curved track as did Landore Viaduct at Swansea - Walnut Tree and Landore both carried double line.

 

A quick Google images stroll around the structures I have mentioned above could, I think, prove very useful to your thought processes as you develop your approach to this site.

Edited January 21, 2016 by The Stationmaster

[gordon s]

Thanks for posting that again, Martin.

 

I knew I'd seen it somewhere.....

[Junctionmad]

 

The only point to bear in mind with such an arrangement is that you need an independent transformer for such secondary circuits, you can't use the one which powers the DCC or DC traction.

 

 

much confusion abounds, ultimately in a DCC layout the track power is referenced to 0V, which is referenced to the layout GND,  however each side of the DCC , may be unipolar around half   the track supply voltage or bi polar around 0V.   since neither track is at 0V, its cannot  be commoned with anything that is 0V.  you can of course have   a single AC transformer  that supplies both the  DC layout power and DCC track power. ( via different regulators ) 

 

The issue sometimes comes , when you derive accessory power by re-rectifying the DCC AC voltage  to create a local DC power supply, in that case a new local 0V is created and again can not be commoned with the system 0V 

 

a 0V line is only 0V with reference to its associated supply voltage, the actual 0V line could actually be at 100s of volts in reference to some other 0V.

 

0V and GND are the same, GND and Earth are not the same , earth can and is used to establish a common 0V ( GND) or it may not be ( i.e. fully floating) 

 

hopefully thats as clear as mud

Edited January 21, 2016 by Junctionmad

[Junctionmad]

Hi Geoff,

 

Why not? Please explain. I can't see any reason.

 

Here is a diagram Gordon if you want to try it. Don't forget the £100 saving on optical sensors or proximity detectors:

 

 

regards,

 

Martin.

Note that this method  may or may not cause a DCC power short, it depends on how the DCC signal is being generated 

 

dave

[gordon s]

Clear as mud?  It is for me.....

 

Just to come back on the clearance issues.  I've normally worked from this sheet.

 

 

I'm far more in agreement with your figure of 60mm, Martin, but this drawing shows 30mm to a bridge pier?  Is that a different structure or are these figures just wrong?.....

 

Seems awfully tight to me.  With SMP at just under 32mm wide, that is just 14mm (3'6") to a bridge pier.  I could probably reach that far leaning out the window if I were 4mm scale.....

Edited January 21, 2016 by gordon s

[martin_wynne]

Thanks for posting that again, Martin.

 

I knew I'd seen it somewhere.....

 

And in case you have forgotten it is based on p.30-32 in "Bridges for Modellers".

 

If the underside will be visible, stick on some 2mm plasticard strips at 12mm centres to represent the cross girders, with brick paper between them to represent the jack arches.

 

Martin.

[martin_wynne]

Note that this method  may or may not cause a DCC power short, it depends on how the DCC signal is being generated

 

That seems very vague Dave.

 

Since no part of the circuit which I posted is connected to the red output line, I fail to see how it could create a DCC short-circuit.

 

I remain convinced that my circuit using one side of the DCC as a layout common return will work fine, unless someone can provide a proper electronic explanation why not. At present I can't see one. The DCC output is a variable mark/space ratio AC square wave at about 18volts. I can see no reason why that prevents it being commoned with other independent supplies. The only possible reason would be related to RF emissions and interference with other equipment. Bearing in mind that it is connected to an entire room full of metal rails, a few extra wires are not going to make any difference. Also I doubt the wave is very square in practice.

 

regards,

 

Martin.

[Junctionmad]

That seems very vague Dave.

 

Since no part of the circuit which I posted is connected to the red output line, I fail to see how it could create a DCC short-circuit.

 

I remain convinced that my circuit using one side of the DCC as a layout common return will work fine, unless someone can provide a proper electronic explanation why not. At present I can't see one. The DCC output is a variable mark/space ratio AC square wave at about 18volts. I can see no reason why that prevents it being commoned with other independent supplies. The only possible reason would be related to RF emissions and interference with other equipment. Bearing in mind that it is connected to an entire room full of metal rails, a few extra wires are not going to make any difference. Also I doubt the wave is very square in practice.

 

regards,

 

Martin.

Appologies Gordon for this diversion 

 

In a typical DCC layout you will use a power supply to generate both DCC track signal and say a DC feed for layout use ( often 12v).  The track DCC signal  is either (a) unipolar AC, where each track pulses goes from  0V to DCC track voltage , in effect creating a track AC voltage that swings about track voltage /2  or a bipolar feed where the voltage on the tracks swings  +- around gnd.

 

The unipolar supply is more popular as the circuitry is simpler 

 

The key thing is ​neither rail of a DCC system is at 0V. both rails are " power rails".  

 

there there is no layout 0V reference at a DCC track.   

 

So you can common DCC derived DC power from DCC track signals,( assuming you always maintain correct polarity)  but not include in that common , the layout 0V derived  unless that DC supply which generated that was truly  floating , which few mains derived DC supplies  are. 

 

so the answer is , you can get a short or not depending on the exact makeup of the DC supply ( and the DCC supply )

 

if you wish to discuss further perhaps a PM and I can sketch it , or Ill post it on templot club , rather then clog up this thread , in MERG designs  for example, to be safe, the lines are connected via optocouplers to ensure separation of grounds 

 

 

dave

Edited January 21, 2016 by Junctionmad

[martin_wynne]

Dave I didn't follow any of that. Gordon isn't using any DC power derived from the DCC output and I agree it would be crazy to common that with the DCC output.

 

What he is using is an entirely independent power supply obtained from RS which has no connection with the DCC power source whatsoever. It could just as easily be batteries. It is entirely floating and could be commoned with the DCC output without any problem at all.

 

However, he has decided not to do that -- and who could blame him after this. Sometimes RMweb is no help to beginners at all.

 

Martin.

[martin_wynne]

I'm far more in agreement with your figure of 60mm, Martin, but this drawing shows 30mm to a bridge pier?  Is that a different structure or are these figures just wrong?.....

 

Hi Gordon,

 

My figure was for the full width between both piers. The actual minimum from the track centre-line to a bridge pier is 7ft-8in = 30.67mm. That gives 3ft-2in minimum clearance from the side of a 9ft-wide vehicle.

 

However, this figure is the absolute minimum on straight level track. On curves it has to be increased to allow for vehicle overhangs and the effect of any cant (superelevation). In practice it is usually wider than the minimum even on straight track. I suggest you set a clearance envelope of say 4ft per side on the dummy vehicle and see how it looks.

 

regards,

 

Martin.

[martin_wynne]

p.s. Gordon,

 

Don't make the structure clearance too wide, otherwise the girders may not be long enough. I recall you found some suitable girders 10" (254mm) long on an American web site. They need to overlap the abutments by about 4ft-5ft each end on the padstones. Say about 20mm each end. The abutments should be angled back slightly, as for retaining walls.

 

Martin.

[gordon s]

OK Martin, doing that the old fashioned way was a bit of a challenge so I would be very grateful if you could check this for me and see if it all hangs together on Templot.  

 

I think it's ok, but feel in some ways I have gone full circle as you may recall I was a little concerned about the angle of the crossing when we first considered changing to a flying junction.  

 

Every dimension has a bearing on the other, so a few mm increase in width can substantially increase the length of the girder spans.  All of those are determined by the need to leave sufficient clearance and once again a few mm here will also increase the length of the girder spans.

 

Here is a pic of my taped prints and pencil drawing.

 

 

The trackbed for the upper double loops in this section is 160mm.  (My normal track bed width of 90mm plus 70mm track centres).  The bridge itself is 140mm wide.  I drew a centre line where the lower track centre line crossed the 140mm bridge width on each side and then measured 40mm each side of that centre line to give me width between the supports of 80mm.  These lines are parallel, but the camera has distorted them so they appear tapered on the drawing.

 

I have placed four brick pillars on each side of the span.  These pillars are 45mm x 20mm and serve the purpose of disguising the change in track bed width from 160mm to 140mm.

 

The dimension between the two inside edges of the pillars on the horizontal axis is 255mm.

 

Measuring across the supports along the line of the double loops gives a measurement of 205mm which with 20mm overhang each side will just about fit.

 

The two possible clash points are on the inside of each curve where there is 25mm clearance between the corner of the pillars and the track centre line.  It's tight, but increasing that will increase the span considerably.

 

As I said at the outset, I would be very grateful if you could take a look at it in Templot.  The dummy vehicle aspects of Templot are very new to me and I haven't yet mastered that particular part of the program.

 

Here's a box file of that particular part of my plan.

 

Martin bridge check 2.box

 

 

Edit:  Just realised I have a problem as the 25mm clearance to the corner of the pillar is below the 30mm minimum...Oh ######!...

 

I may have to reduce the 45mm pillar dimension to get the additional 5mm.

Edited January 21, 2016 by gordon s

[martin_wynne]

Hi Gordon,

 

I have moved the outer green curve a fraction, to get a better angle through the bridge and a more gentle S-curve transition. Otherwise it would need longer girders. The new track is blue:

 

 

I realise you may have already fixed the green trackbed for this. If it is not wide enough to accommodate this change I will start again.

 

You have rather lost me with your brick pillars. I suggest reducing the trackbed to 139mm wide over rather more than the minimum length, it is easy enough to rebuild scenic work to fill any gaps. You need at least 260mm length to fit the girders on the sides of it.

 

I set the clearance to 3ft each side on a 9ft-3in wide vehicle. This makes 30.5mm model clearance from the track centre-line on straight track.

 

The critical point is the front left corner as you discovered. There is just about enough space to support the girder on a sensible-sized padstone and maintain clearance for the vehicle below. It could have been made a lot easier by moving the green tracks just a few mm closer to the baseboard edge, but you seem to have changed the design from the last one I saw?

 

The abutments are 90.6mm apart (square across) giving a span on the girder centres of 208mm. The 10" 254mm model girders are just about long enough.

 

The track is offset sideways under the girders because of the different curves at each end, which might look a bit odd. You could fill the trackside space with some p.w. clutter to make it less obvious. The middle and rear girders could be shorter, but that might look a bit strange, and not so convenient as using the ready made ones as-is.

 

Here are some screenshots and a video showing the dummy vehicle running through:

 

 

 

 

Video: https://flashbackconnect.com/Default.aspx?id=wzLCL9io_iJRlpxC8FL86A2

 

The girders are shown 8mm wide for the top flanges (white dotted).

 

I will post the .box and .bgs files after breakfast.

 

regards,

 

Martin.

Edited January 22, 2016 by martin_wynne

[martin_wynne]

Hi Gordon,

 

Here is the BOX file. RMweb has scheduled maintenance today so I will post it on Templot Club too. Also the BGS file.

 

gordon_new_bridge.box

 

regards,

 

Martin..

[gordon s]

Many thanks for that, Martin.  I had a good nights sleep last night and somehow that always seems to work.  I'm convinced that you can keep looking at a problem and then have total blindness.  Taking a break and coming back to it the next morning seems to provide clarity that wasn't there before...

 

I have already cut the trackbed, but that's not an issue as I want to get it right.

 

Here's my revised version this morning.  I set the track bed width of the lower single track to 60mm, knowing that would provide the 30mm minimum clearance required.  As it stands there is likely to be a retaining wall running parallel to the double tracks above.  The trackbed at that point is 160mm wide which reduces to 140mm wide over the bridge section.  The brick pillars were my idea to cover the join from the retaining walls either side to the bridge supports.

 

I have managed to meet the 30mm minimum clearance on the corners and the current width between the two bridge supports is 75mm and the dimension across the bridge supports when measured along the double track is 195mm.  Allowing a 20mm overhang each end would mean plate girders of 305mm as they are mounted on the diagonal.

 

Although the girders I found in the US were 254mm long, I have no problem making custom girders from either Wills or Peco components and did exactly that in earlier versions of ET.

 

I'm interested in the transition from the retaining walls to the bridge supports.  That was an unknown for me, hence the idea of using pillars.  Your method seems to have reduced the overall length of the spans by 50mm, so that may be a much better solution.

 

I'm just off for breakfast and will take a proper look at your plans later this morning.

 

Many thanks for taking the time to look at this challenge.  I have no doubt we'll get there!.....

 

 

 

 

 

 

[islandbridgejct]

Hi Gordon,

 

I'm a bit concerned about that 32" radius on your inner storage roads - not that I think they won't work, but that, based on past experience, I'm afraid you will later cite it as one of a number of compromises* as a result of which the design no longer satisfies you. I don't think I could go through another episode of you ripping everything up. (Sorry.)

 

The argument against the 32" radius, I think, is this: you suggest you might use it for goods trains which will have short wagons. However, you're likely to want to have those trains pulled by long wheelbase steam engines, a WD, 9F or 2-8-0. These may object to the tight radii. Even the larger 6 coupled engines might object to those radii. You will then feel that only diesel stock can use the tighter roads.

 

I wonder would it be possible to relax the radii by taking the turnoff from a different point, and either shorten or lengthen the loops in question (or lose them altogether, or make them single-ended if you have to).

 

Alternatively, if you decide you're happy** with them, I'll have to ask the subscribers to this thread to gang up on you and refuse to allow you to scrap this build until everything is completed.

 

(The current scheme is turning into a really layout design master class. Thanks.)

 

Alan

 

 

* No other compromises detected in this build yet.

** Actually really happy with no complaints, quibbles, worries, reservations or unease whatsoever.

[RedgateModels]

The argument against the 32" radius, I think, is this: you suggest you might use it for goods trains which will have short wagons. However, you're likely to want to have those trains pulled by long wheelbase steam engines, a WD, 9F or 2-8-0. These may object to the tight radii. Even the larger 6 coupled engines might object to those radii. You will then feel that only diesel stock can use the tighter roads.

 

 

 

a 9F will handle Raduis 2 curves (either Bachmann or Hornby) with is half the radius Gordon is proposing, it will be fine