T Gauge - Monbulk Creek (Australian Narrow Gauge)

[martink]

I have been modelling in T Gauge for several years for UK and Australian prototypes.  After becoming disheartened with the physical and electrical limitations of conventional T Gauge, I looked for an alternative and settled on a custom variation of IDL Motors' (teenytrains.com) linear motor drive system.  I have developed my private own version of this, with their permission, and over the last two years have been building a series of small, experimental exhibition layouts of increasing size and complexity.  IDL has recently allowed me to let a few other people make use of this work, including a contributor to this forum (Sokramiketes) who is starting on a small CP layout.

The first of these test layouts was Monbulk Creek, depicting a locally well-known horse-shoe trestle bridge on a 2'6" heritage railway on the outskirts of Melbourne, Australia.  This 37" x 15" layout  was built in 1:350 scale with what would be 2.2mm track, just qualifying it as a micro-layout.  The track plan is a simple dogbone, half hidden behind the backscene, with some basic automation that allows three trains to take their turn running through the scenic section.  The chosen trains are typical of current day (well, pre-Covid) tourist operations, including the mandatory fire patrol trolley required for steam operations in Summer downunder.

The sectional track system consists of small doubled-sided printed circuit boards, with paper overlays to make it look more like rail track.  The controller/throttle is similar to a conventional PWM unit, but with three wires instead of two and generating a different sequence of pulses.  The trains are 3D printed body shells with embedded rare-earth magnets instead of mechanisms, which slide along the smooth track surface (i.e. no wheels).

The linear motor technology has a completely different set of strengths and weaknesses than conventional model rail.  Its biggest plusses are extremely high reliability with low maintenance, very low speeds, long trains, steep gradients, ease of automation and applicability to road and canal models as well as rail.  Its biggest weaknesses are not being a true railway with wheels rolling on rails, inherently jerky motion, track spacing issues due to the powerful magnets in the trains and high electrical complexity for non-trivial layouts.  It is best suited for the ultra-small scales, certainly given the design trade-offs I have used in this version.

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[dem34]

That's awesome, and I bet sound wise the low electronic beeping beats the coffee grinders found in traditional T.

Now I have to wonder on the topic of jerkiness, would it be at all possible or even feasible to put some kind of non magnetic bearing embedded in center of the rolling stock to improve smoothness?

[martink]

The jerkiness has several related causes.  The main reason is that as each set of coils in the track is powered in turn, the trains leap forward so that their magnets line up over them.  With larger and heavier models, or at high speeds this would be a smooth continuous motion but at lower speeds the models have time to slow down and speed up with each step.  The basic step size with this system is 1mm, which is painfully obvious at low speeds, so I use the trick of rapidly oscillating back and forth between two adjacent states in varying proportions to simulate a smaller step size of 0.25mm.  This allows me to get decent results down to 2mm/sec, which is about 1.5mph in this scale.  The second cause is that the amount of force applied to the trains when advancing a single 0.25mm microstep is minuscule, and sometimes not quite enough to overcome friction between the model and the track.  This means that some vehicles in the train can hesitate slightly and then catch up again when the force increases with the next microstep.  A third issue comes from the pattern of coils in the track which repeats every 12mm - the forces vary slightly within this pattern and cause a bit of side-to-side wobble. As with most things, the idea is to find the best working compromise.

The trains are not exactly silent either.  The combination of track and trains forms an electric motor with a lot of very loose, rattly parts!  The higher frequencies generated when using the 0.25mm microsteps are in the audible range and make it worse, very much like using a conventional low frequency PWM controller, so the trains buzz and growl as they move along.

[Sokramiketes]

Great to see you here on Railwire, Martin!

The sound and the slight jerkiness are completely outweighed, in my mind, by the consistent and reliable operation you've been able to achieve. 

I think Jesse put it best, it's a great modeling scale but T gauge doesn't run well enough.  (http://jessestmodels.blogspot.com/2019/06/the-case-for-t-scale.html)  The linear motor concept changes the game entirely. 

[martink]

And for what it is worth, here is a video of the final layout.  I have thought about going back and revisiting it, adding extra detail (more trees, telegraph poles, signs, still more trees, etc.) and building freight stock from a century ago when it was a working line, but prefer to put the time and effort into new projects.

[martink]

The sound and the slight jerkiness are completely outweighed, in my mind, by the consistent and reliable operation you've been able to achieve. 

I think Jesse put it best, it's a great modeling scale but T gauge doesn't run well enough.  ...  The linear motor concept changes the game entirely.

I obviously feel the same way.  It takes a great deal of work to get any sort of reliable running in standard T, and even then there are far too many frustrating limitations.  While the linear motor approach certainly has its own collection of drawbacks and limitations, its potential for reliability, slow running and long trains allows many of the things T could and should have excelled at.

[Lemosteam]

@martink I am totally fascinated, but have some questions.

Is the magnet spacing and quantity per car required?

Could only one magnet at each typical truck (bogie) center still work?

What size are the magnets?

Can the cars and tender be coupled together, and if not sure, what happens if you do?

Printed side frames and wheels could just go along for the ride and would hide the magnets.

Have you thought about clear matte adhesive backed mylar for the track surface?  These can be printed on with a laser jet printer.

[martink]

Some good questions there...

@martink I am totally fascinated, but have some questions.

Is the magnet spacing and quantity per car required?

Could only one magnet at each typical truck (bogie) center still work?

What size are the magnets?

Each magnet is roughly equivalent to a powered axle on a conventional train, with similar issues to contend with.  More magnets mean more traction and better steering, but too many magnets cause trouble negotiating the curves.  In practice the best combinations are 4, 8 or 4(gap)4.  The magnet spacing and positioning has to exactly match the coil spacing on the track, and with this track design that means 3mm centres with alternating N/S poles.  The easiest way to do that is to use 3mm diameter disc magnets, which naturally snap together into the correct alignment. There also needs to be a 12mm (4-magnet) gap to the next car's magnets to avoid mutual interference and jack-knifing.  This is turn means that certain chassis lengths work best, cramming in as many magnets as possible even though they don't line up with the correct bogie/truck position on the model.  The best lengths for carriages are multiples of 12mm, with a minimum of 24mm (23mm body plus 1mm gap) using a block of 4 magnets.  Given the short narrow-gauge rolling stock on this line, the layout scale of 1:350 was chosen specifically to match this figure.  I originally planned to do this layout in 1:450 scale, but the 18mm coaches did not work reliably, nor did the next try with 21mm and 1:400.   

Can the cars and tender be coupled together, and if not sure, what happens if you do?

The 24mm minimum length issue is the key factor here.  Trying to actually articulate the Garrett (2-6-0+0-6-2) just did not work, nor did separate tenders for steam locos on later layouts.  The same thing applies to short UK 4-wheel wagons, where I ended up putting two bodies onto a single chassis.   

I also tried actual couplings between cars rather than simple pins, but that did not work out too well.  The controller generates pulses to the coils that move the train in 0.25mm steps.  The amount of force applied for such a short jump is very small, and sometimes not enough to overcome friction with the track, so sometime the carriage doesn't move until the next step to 0.5mm adds more push.  This causes a bit of a shuffling motion which is more-or-less synchronised along the train, but when I tried hook-and-socket couplers to try and improve this, the laggard car gets jerked along unpredictably and it just did not look right. 

Printed side frames and wheels could just go along for the ride and would hide the magnets.

I tried this on my latest layout, but it was not satisfactory and it was tricky to apply to the models.  At any normal viewing distance, just the suggestion of wheels with a bit of 3D relief and a different shade of grey paint seems to work well enough.  Each of these layouts is an experiment - I try different techniques to see what works best.

Have you thought about clear matte adhesive backed mylar for the track surface?  These can be printed on with a laser jet printer.

I have used several approaches for the track surface, from simply painting the track (bad move), to clear styrene sheet painted on the underside (first mini-layout), to normal paper printed with imagery from AnyRail (this layout), to self-adhesive label paper printed with imagery from a custom program (later layouts).  I haven't tried Mylar, but it sounds worth a go - I might give it a try on one of my little test tracks.

This a shot of some of the trains from my latest layout (#3) - it shows my best efforts so far with magnet spacing, couplings, underframes, general finishing, etc.  It should clarify a lot of the above.

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[Lemosteam]

@martink that all makes much sense.  Thank you so much for the info!

I would also think that the coplanarity of the magnets in the car helps with smoothness, so I assume you line up the mags on a metal plate before you adhere the carbody to them.

can the "track" be purchased in individual sections or is it one long PCB strip?

One more, I assume this would not work on anything but near-flat track elevations, right?

Byt eh way, that last shot looks like a nice PRR K4, (lol, I know many Australian steam had Belpaire boilers)  ...

[DKS]

Another thought about track... and what I'll be trying for my layout:

Print the track image in color on self-adhesive paper, then laminate it with Avery 18665 clear label material, which has a flat finish and is very thin.

This way the image is protected from wear by plastic that isn't shiny.

[martink]

@martink that all makes much sense.  Thank you so much for the info!

I would also think that the coplanarity of the magnets in the car helps with smoothness, so I assume you line up the mags on a metal plate before you adhere the carbody to them.

A 6" steel rule is far and away the most useful tool for working with those magnets - even for finding them when dropped on the carpet!

The alternating N/S pattern is used to reduce the effective step size and get better, smoother low speed running.  The coils on the track are in three interleaved strings on 2mm centres, and are always driven so that one string is North, one South, and the last Off. With coils 2mm apart, and the magnets 3mm apart, when driven correctly you get a 1mm step with the magnets never quite lining up over the coils.

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can the "track" be purchased in individual sections or is it one long PCB strip?

The track pieces are generally around 100mm long (the black U-shaped thing in that last pic is my standard 96mm straight - and there's that 12mm figure again).  For a new layout I design one or two panelized PCBs with 6-10 different pieces on it plus a mix of joiners, then get that built as a batch of either 10 or 20.  They then get soldered together into a complete mini-layout.  I have attached an under-construction pic which might make this clearer, although I neglected to take a full bare-track-on-bare-board one of this layout.

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One more, I assume this would not work on anything but near-flat track elevations, right?

Wrong.   Every vehicle is self-propelled, so unlimited length trains can run up a 10% gradient.  However, the system does not cope well with sideways tilt, so any sort of cant or camber has to be avoided at all costs.  Since this layout was my first attempt, I built it all on the flat even though that bridge should be at the bottom of a dip.

Byt eh way, that last shot looks like a nice PRR K4, (lol, I know many Australian steam had Belpaire boilers)  ...

It actually is a pair of UK GWR Hall class 4-6-0s from my latest layout - most British companies had adopted the Belpaire firebox by then.

[martink]

Another thought about track... and what I'll be trying for my layout:

Print the track image in color on self-adhesive paper, then laminate it with Avery 18665 clear label material, which has a flat finish and is very thin.

This way the image is protected from wear by plastic that isn't shiny.

I use self-adhesive label paper with a suitable track design printed on my little inkjet, and with multiple coats of matte acrylic spray to protect it - that works very well. 

[Lemosteam]

Aha.. But all grades com to an end whether going up or coming down, correct?

Exaggerated:
   _
_/

How do the magnets and cars handle the grade transitions in the vertical plane, or I assume that must be a very gradual curve?

[martink]

Aha.. But all grades com to an end whether going up or coming down, correct?

Exaggerated:
   _
_/

How do the magnets and cars handle the grade transitions in the vertical plane, or I assume that must be a very gradual curve?

Yep.  A gradual vertical curve.  The PCB material is thin and quite flexible, and I use a thin plywood trackbed which is also flexible, so they naturally form a smooth transition, typically over 6" or so.  The most extreme gradients I have tried so far were on an early experimental road layout that I never took to completion: