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Monbulk Creek

Postby martink » Sun Mar 31, 2019 6:21 am

I keep getting diverted onto all sorts of weird and wonderful projects. Here is one that has reached an interesting stage.

The Monbulk Creek trestle bridge is a popular viewing spot on "Puffing Billy", a 2'6" gauge tourist railway on the outskirts of Melbourne, Australia. This layout will be a 1:350 scale model of that spot, with 3D printed Victorian narrow gauge trains running on my linear motor tracks.

The layout is now functionally complete and nearly ready for the scenic work to begin, although the trains and bridge are still only test pieces and need more work. Overall size is 37" x 15", just qualifying as a micro-layout (up to 4 sq ft).

Video:
https://youtu.be/w3ZlAIuZqGU

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Re: Monbulk Creek

Postby kajovog » Sun Mar 31, 2019 7:12 am

Wow, you are really coming along with the linear motors tracks. It works really well.
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Re: Monbulk Creek

Postby msimister » Wed Apr 03, 2019 8:28 am

Hi Martin,

That's brilliant.

For an electrical dumbo like me, can you explain how the linear motor and track work, please:

* Does the rolling stock have wheels or does the linear motor just drag the locos and carriages along the track?
* Is there any track or is it just paper, per the blurb in the video?
* Assume you 3D printed the Garratt and other rolling stock? Looks pretty realistic (I'm a guard/signalman on Puffing Billy)

Thanks in anticipation

Cheers,

Malcolm
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Re: Monbulk Creek

Postby martink » Wed Apr 03, 2019 9:55 am

Each piece of track is just a small PCB (printed circuit board), and these are connected (soldered) together to form a layout (after checking the plan in AnyRail), just like a normal model railway. The PCBs have no components on them, just three wires forming three interleaved strings of coils (electromagnets) on 2mm centers. The controller is basically a modified PWM design that powers each of these strings of coils in succession, so that anything with a magnet gets dragged along like a conveyor belt.

The paper surface serves two purposes: improved appearance and smoother running. Vehicles running directly along the coils sound like they are moving on cobblestones, which in effect they are. The same technique also works really well for roads - I will be able to print all the necessary road markings, customised and true to scale.

The 3d-printed vehicles have flat undersides with holes for small disc magnets, and just slide along on those magnets. Each vehicle is effectively self powered, and the biggest difficulty was getting them to move in concert in a proper train-like manner. It is like herding cats! The design I have settled on (for now) has a horizontal coupler pin at one end and matching socket at the other, purely to keep the vehicles in line and reduce sway, especially on the curves. Imagine mounting a long coach body on a very short 4-wheel chassis, and you should get an idea of the problem. With longer coaches, I could space the magnets out and effectively group them into bogies, but not with the short Puffing Billy stock.

And yes, all the stock is 3D printed, but they are still only trial pieces. Ditto for the bridge. Since I now know how much detail I can actually print, I will tweak them for the best result. The NBH coaches in particular need work, but I think I can see how to get them looking right, even to the people sitting in the windows with their legs hanging out.

When comparing it to conventional T gauge, the linear motor drive has some really painful drawbacks (no wheels, an inability to do short 4-wheel wagons or less than triple-track spacing), but some equally impressive advantages (reliability, low-speed running, full-length trains, easy automation, road/rail interaction). I now want to see how far I can take it all. Also, I have been marveling at the work of some of the micro-engineers here, so have to carve out a unique niche for myself!
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Re: Monbulk Creek

Postby msimister » Thu Apr 04, 2019 10:07 pm

Thanks Martin. That's very helpful. Very interesting stuff. Couple of further questions:

* Can the PCBs, magnets and electrical controller be purchased commercially or did you make your own? If purchased, where from?
* Can you make 'points'. If so, that would be another big advantage of linear motors.

I assume you're aware of the leg-dangling ban on Puffing Billy? For those not aware (most of you probably), Puffing Billy used to allow passengers to sit with their legs dangling over the side of the open-sided carriages, which was very popular. However, about a year ago, a mini-bus ran into the side of a train on a level crossing (bus driver's fault); fortunately, no one on the train was injured but the Office of the National Rail Safety Regulator banned leg dangling and that ban is still in force.

Martin, I'm sure PB would be interested in your model...

Cheers,
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Re: Monbulk Creek

Postby martink » Fri Apr 05, 2019 11:35 am

All the key patents are owned by IDL Motors, so anything I do with it must be purely for my own use. Alas. That said, the magnets are off-the-shelf, and the controller is a straightforward variant of standard PWM/stepper motor controllers. I've helped a couple of people build one to get better control of tracks they have bought from IDL. The tracks, however, are the kicker. I design the PCBs and get them manufactured by a standard commercial PCB fab, and my out-of-pocket costs for the finished track work out to about AUD $15-$20 per meter.

Points are in the pipeline at this time. I have done preliminary proof-of-concept experiments, but have yet to actually build one and integrate it into a test layout. A real pain to drive from the electrical side, so I won't use many on any single layout. Test layout #2 design is underway, so soon now...

Leg dangling on Puffing Billy? Yep, well aware. I think I can see how to do that properly on the NBH models, so back to the good old days. And when finished, the layout will turn up at one of the local shows, where PB always has a stand.
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Re: Monbulk Creek

Postby martink » Thu Apr 11, 2019 8:16 am

The scenery is beginning to take shape. Literally.

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Re: Monbulk Creek

Postby martink » Sat Apr 13, 2019 2:54 am

The first hint of what it is meant to look like...

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Re: Monbulk Creek

Postby martink » Sat Apr 13, 2019 7:33 am

The initial rough painting is done, ready for grass and surface texture...

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Re: Monbulk Creek

Postby martink » Sun Apr 14, 2019 3:16 am

And the scatter has been applied. Now for the fiddly bits...

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