T-Gauge Point Motor Demonstration

In an old post I explained a very simple method to first modify and then motorise a T-gauge point unit. Well, to prove the concept, below is a video demonstration.

In addition to the modified point unit and servo you will also see a PC and Arduino controller. The Arduino is the eventual controller for the layout but a separate servo controller interface will be needed to power more than a couple servos. Using the pulse-wave modulation (PWM) from Arduino outputs for servo and train motor control will be a feature of future posts. 

Viaduct

One of the charms of T-gauge is being able to model big infrastructure items like bridges. And one of the problems with T-gauge is the scale you are working in... tiny tiny tiny. Luckily, as things get smaller, details become invisible without any loss of visual effectiveness.
To date I've been experimenting with Scalescenes scratch building texture prints, printed onto card and paper. Now, the requisite thickness of card and size of structural items means a structure built solely from card in T-scale would not have sufficient strength, and the alignment of components would inevitably go awry. The simplest solution is first to build a sub-structure from balsa and paper texture prints to the balsa - the paper immediately and easily taking the form of the balsa. A resultant 12-arch brick viaduct is pictured below.

Balsa-paper viaduct with HST.

The balsa form for the viaduct was drilled using a 25mm drill bit and a craft knife was used to create the piers from these holes. Texture printed card was glued to outer faces of the structure and a (very) sharp craft knife was used to cut away the spans. Separate strips of texture printed card were glued to the inner faces of the arches / spans. Finally, to mask the gaps between the outer face and inner face card, thin strips of texture printed paper (mimicking brick voussoirs in this case) were folded  (and to permit the bend around the arch, cut perpendicularly to one edge of the fold) and glued in place.

Voussoir detail of the arches.

Some remaining details still need to be added to the viaduct. The track is to have cess ballast added, which will (intentionally) raise the height of the cess to near-level with the viaduct wall. So naturally, some fencing needs to be added and luckily EMA model supplies do a small range of etched brass products in 1:500 scale. In the photos you may be able to see small grey protrusions from the outer faces - these are anchor points for future electrification structures. And finally, the (stone) foundations for the viaduct piers will be added when it is finally glued into position on the layout.

T-Gauge Point Motors

Pictured below is your typical T-gauge point unit. You will see it has two tiny switch rails, and these are moved by a gentle push on one of the tiny tabs you see on the outside of the point unit. Magnets integral to the point unit grab the closed switch rail keeping it tight to the nearest stock rail.


T-gauge point unit.

The design of the point unit is less than desirable - the switch detail is quite poor and the large insulated section can leave trains stalled - but to scratch-build would be a challenge too far for me (but evidently not others.)

The biggest drawback is the lack of provision to motorise (actuate) the point unit. Motorising the point unit is a must and here's my take on how to do it.

Firstly, if you flip-over the point unit you will see two small screws on the underside. Undo these and you will see that the switch assembly drops out.

Underside of point unit with switches removed.

On closer inspection of the switch assembly (see the next picture below), you will see the switch rails fit snugly into a bracket plate, and the switch rails can be gently pulled free. The switch rails are moved by a drive switch plate that has lugs between which the switch rails sit; when the drive switch plate is moved the lugs move the switch rails. Finally, a magnet held underneath each stock rail by the bracket plate grab one of the switch rails if it is within 1mm.



Switch assembly showing alterations for fitting with a motor.

The picture above also shows the main alteration needed to fit a point motor. I have drilled a hole in the switch drive plate and cut a corresponding slot into the switch bracket.

The final alteration is to file or cut a small notch into the point unit that corresponds with the slot in the switch bracket, as pictured below.

Point unit with slot cut/filed into it.

Then simply re-assemble. Put the switch drive plate onto the switch bracket. Insert the switch rails back in switch bracket, aligning them with the lugs on the switch drive plate. Place the assembly back in the point unit and replace the screws. Finally, push the switch magnets into place from the underside of the point unit.

And for actuation? A small servo (sub 10g type will do) with a steel rod connected to the servo arm and cut to length to thread through the hole you've just cut in your point unit. The servo can be connected directly beneath the point unit (as shown below) or else the connecting rod can have a 90 degree bend to allow the servo to be mounted to the side.

Servo connection to the point unit.

  

All told, it takes about 15 minutes to make the alteration and then you've got yourself a T-gauge point motor actuating a T-gauge point unit!

The observant among you might be wondering how to control the servo. All will be explained in another post.

Controlling Two or More Trains on the Same Line?

The planned layout has long sections allowing multiple trains per line. Which presents an interesting set of problems:

• How to create block control in T-gauge?
• How to individually control each train on the same line?
• How to supply power to each train?
• How to vary the power supply to each train for speed control and reversing?

T-gauge is just too small for DCC to be feasible. So...

A schematic of the proposed solution is pictured below.



Schematic of train control concept.

The concept solution is as follows:

• Divide the line into blocks, with overlaps.
• Electrically separate the rails of adjacent blocks.
• Fit train detection to each block and overlap.
• Use software and PC to monitor occupany of blocks.
• Assign in software a unique ID to each train.
• Use software to 'follow' a train as at occupies and clears each block.
• Provide one speed controller per train.
• Use pulse-width modulation (PWM) with H-bridge to generate a variable voltage in proportion to each speed controller.
• Use software and hardware to switch using relays the PWM power from block to block, tracking the movement of the relevant train.
• Isolate power to a block by switching off the relevant PWM power if the occupying train is detected at the overlap and the next block is occupied by another train.

The schematic above shows only two speed controllers per line, i.e. two independently controlled trains per line, but more can be added. The complexity of doing so involves adding additional relays per block section to switch the additional power supplies connected to each block.

Finally, for the concept to work, train detection must be able to detect all vehicles of a train are clear of a previous overlap. Thus 'presence' detection is insufficient; a continuous train detection system is required. How to achieve this in T-gauge will be the subject of a future post - but it can be done!

Layout Plan

Cutting to the chase, here's my proposed layout.

 

Track plan using (mainly) off-the-shelf set-track components on a 1220mm by 607mm baseboard.

And here's how and why I developed it...

All railways are built with a purpose in mind and models are no different. And trains travel from A to B, so it's helpful to have at least an A to justify the existance of trains.

I'm mainly interested in construction and less so the operation of trains - but I would like to see long trains sweeping through expansive landscapes. Due to the super tinyness of the trains, T-gauge does not offer much scope for marshalling so any sidings will only be used for fixed formations. Lastly, off-the-shelf T-gauge rolling stock options have more than a small bias towards modern UK trains, which of course tend to be fixed formation.

Putting this together, my planned layout will consist of:

• A UK setting.
• A two-track main line railway, as is common in the UK.
• A main line that loops to maximise the visual effect of trains moving through the scenery.
• At least one station with two platforms long enought for the T-gauge HST.
• One or more stations with platforms long enough for a typical regional passenger EMU or DMU service.
• A freight container terminal to justify running a locomotive or two pulling a long rake of wagons.
• A headshunt within the freight terminal to enable the shunting of freight trains clear of the main line.

Now for determining constraints. These are essentially the size of the board, how much of that board I want (can afford?) to fill with track and what type of track to use, the latter having been answered in my last post.

A quick read of some websites on baseboard building, selecting a plywood top, and after trip to the local DIY store I have chosen a base size of 1220mm by 607mm to save effort on cutting whilst having a layout that is relatively easy to lug about. Such a board size will leave plenty of room for the largest radii set-track curves.

As for layout planning, there is software for T-gauge such as AnyRail but I've used Microstation CAD software and created standard cells using the T-gauge track specifications. Or you could cut yorself some paper templates and plan it on the floor of your front room.

Plain Line Track Options

Railways begin and end with track. And so too will the T-gauge model railway. Before layout planning begins there needs to be some though about the track construction technique to be adopted - after all, the track alignment will have to fit the track construction.

The first thing to note about modelling in 1:450 scale is: compromised detail does not (always) compromise the effect. The second: seriously small things need seriously precise manufacture.

The Options

As of February 2013 there are only two manufacturers of T-gauge track components: The Railway Shop Hong Kong; and you. For most railway modellers, attempting to hand-lay track is not a serious consideration (although check out David K. Smith) so we can eliminate that and focus on the products of The Railway Shop, which offers:

1. Set-track; or
2. Flexi-track.

1. Set-track.

2. Flexi-track (brown wood sleeper or grey concrete sleeper).

A full technical specification for the set-track can be found at t-gauge.net. A general comment about T-gauge track is it is not exactly to scale: it's real-sized equivalent rail would be 270mm wide! However, the effect is not spoiled by this inexactitude.

A comparison of purchased set-track and flexi-track has found:

• Set-track
• Pros: easy to assemble; no risk of excessively tight radii leading to train derailment; accurate straight alignments; easy-to-achieve parallelism of adjacent tracks; and a useful cavity beneath the integral track bed for installing possible train detection devices. 
• Cons: out-the-box plastic look; lots of large bright-gold rail-to-rail connectors due to the short length of individual set track sections; lack of integral  ballast texture; gaps between the ballast of set-track sections; fixed range of curve radii to choose from; and no transition curves (which can reduce the visual impact of smaller-than-reality curve radii); 
• Flexi-track
• Pros: you can install any track alignment you want, including large-radii curves; the technique you use to ballast the track is your own personal choice; and fewer rail-to-rail connectors.
• Cons: difficult to uniformly bend into required radii; difficult to fix straight; delicate rail supports that are prone to separating from the rails; lots of ballasting to be done; and less-than-simple connection to turnouts (which are all currently of set-track construction with integral track bed).

Another potential concern about the set-track is the track interval (the space between tracks) is not to scale. In the UK the standard track interval is 1970mm or in T-scale 4.4mm, whereas the T-scale set-track interval is 8mm. The 3.6mm difference is explained by allowances for the swept envelope of passing trains around the tight curve radii of the set-track which, due to the lack of transition curves, continues on to straight track. The impact of this compromise is the visual effect of passing model trains having acres of space between them when real trains have very little. In practice, if you plan to use non-scale curve radii with flexi-track, curved track intervals will still need to be not-to-scale and to reduce the visual impact of this you will probably continue this on to the straight track so nullifying the benefit flexi-track offers in this respect.

Selected Option

It probably appears to you readers of the blog that flexi-track wins over set-track. And it probably does. However, for my planned layout out I envisage a two-track railway (as is common everywhere in the UK) and this demands good parallelism between adjacent tracks on curves and straights. On this advantage alone I am going to choose set-track.

Having selected set-track, the challenge ahead is to improve the look of it and overcome some of those cons: plastic look, large bright-gold rail connectors, etc, etc, etc...

Teeing Off

Anyone who's ever seen a railway will appreciate the scale: simply massive. It's perhaps this impressive enormity of scale that attracts people to model railways. But that same scale, even when reduced to lilliputian-tinyness, still remains a bit too big to model anything but small chunks of real railway.

Enter "T gauge" in  the scale of "T". T-scale is 1:450 scale, compressing 450 metres of real railway into every 1 metre of your model railway. Put another way, you can get 3 times as much railway using T-gauge as you can using N-gauge.

With T-gauge it seems possible to model big landscapes or run realistically-long intercity trains like the one below and not have to create the necessary space by kicking-the-kids-out / losing-the-dining-room / divorcing-the-wife / etc.

T-gauge pencil-sized British HST courtesy of TGauge.co.uk

Which neatly brings us to the point of this blog. I've always fancied a model railway that models the trains I see: long thin formations snaking through cuttings and stretching over viaducts spanning deep valleys. And I'm going to attempt to do so in the scale of T. This blog will keep you posted on how I'm designing and building my T-gauge model railway.