layout planning - geometric calculations for asymmetric layouts

[miyakoji]

I've been playing with XTrackCAD, trying to use track pieces (Tomix in this case, but regardless, no flexible track) to make layouts with varying shapes, curve radii, etc.  But, as I should have expected, the track often doesn't link cleanly when I get back to where I started.  I've googled on search terms like the title of this thread, but I haven't found the information I'm looking for.  Maybe there isn't a proper method to this, but I thought I'd ask:

 

Is there a way to use geometry to properly plan a layout?  For example, I tried to implement the general shape of the outer loop of this layout: http://www.anyrail.com/system-specific5/h0_atlas-code83/h0_atlas-code83-dave-gann-1_large.png featured on http://www.anyrail.com/examples_en.html with Tomix pieces.  Didn't work.  I'm not trying to do anything (yet) with grades.

 

Thanks!

[Densha]

When recreating a layout with another type of track (thus other geometry as well), you have to find a way to make a layout that resembles it but you can't make it exactly the same because of the other geometry. It looks like the layout you linked to features flex track as well...

[disturbman]

There is but involves a lot of calculus. At least Tomix's tracks have quite a simple geometry and it is easy to calculate roughly what is needed. Do not forget that Tomix do have one piece of track that can vary in length.

But yeah, it will be a tedious trial and error process.

[kvp]

First you try to get the general shape in order. Then you find the meeting point and place the last curved section in a way that only straight sections are needed to connect them. Then you use a backtracking algorithm to find the best matching small pieces that fill the distance correctly. I've drawn the layout you mentioned using tomix finetrack as an example (without using flextrack):

 

(can't upload the .scarm file, it's not allowed)

[cteno4]

Miyakoji,

 

That plan uses flextrack sections to fill in the gaps in sectional mismatches. When you use multiple curves you will in up many times with mismatches like this in sectional curves. It takes a lot of playing to get them to line up and sometimes a small straight piece in your 180s to make different ends with different curves match up.

 

The realizable straight section also helps work out these kinks but keep them away from being right near points, curves or cross overs as they can sometime cause issues there. You can also get cleaver with the combos of the different sized small pieces to come up with odd lengths. Also you have a fair bit of play in a good sized loop as well so you can also fudge a little bit!

 

This is the down side of sectional track in that you can't get really georgous Bézier curves and easements, etc. Sectional gives you a but chunkier design.

 

Cheers

 

Jeff

[Mudkip Orange]

Here's what I'd say.

 

---Every sectional track system has a maximum radius, and you'll never get sweeping curves that are broader than that radius. For Kato this is 718mm, for Tomix it's 605mm.

 

---If you're building a layout with Tomix you can use the 541mm-15d and 605mm-10d pieces interchangably to fine-tune the angles of a tangent (straight) track

 

---If you have an idea where you want two curve pieces to go but don't know how to put a straight track in between them, set your units to metric and then connect with flextrack. Then you'll have the total length of track and figuring out which straights to assemble is a matter of addition and subtraction.

 

---If you have an idea what angle you want a tangent to be, draw it and then look at the angle in Xtrak. That'll give you an idea of what curve pieces you need to use to get it.

 

So for instance, here's the layout you linked to in Tomix:

 

[katoftw]

The problem with using component track pieces like Kato/Tomix is that it creates symmetry. Or they were designed with symmetry in mind from the get go. So symmetry will be a product of any layout design.

 

There are ways of breaking up the symmetry to make a layout look asymmetric. Ie- if you have a layout with R280/317 on each end. You could replace some sections with R354/391 (including the opposite side of cirlce/curve to create more of an oval shape at one end of the layout. Or add a straight section somewhere in the curve to create a difference angle.

 

It's not hard, just requires some playing around and experiementing.

 

Tomix I think is the easiest to do it with. Two S18.5 equal 37mm, so easy enough to have different radi curves at opposite ends of your layout.

Edited August 3, 2014 by katoftw

[katoftw]

I was just looking at some Tomix stuff, and turns out S72.5 is the same length as a S70 if turned 15 degrees. Same goes for a S99 turned 45 degrees. These could be added in to really mix up the turns, and all you need to add to a linking straight is a S70 piece.

Edited August 3, 2014 by katoftw

[E6系]

Hello Miyakoji,

 

Must I really give such an experienced modeller a lesson on Tomix Finetrack?  I am surprised!  ;)

 

Firstly, let me say your question has been discussed many times, but not on JNS.  It is true that with Tomix you are limited to the radii provided in the catalog.  But you are not limited to 15° increments of angle.  It is true that Tomix supports the 15° increment by providing the S72.5 track piece, and 45° with the S99.  These pieces are used to bring you back onto the 70mm grid.  But did you know Tomix supports ANY angle and freeform track planning?  It is true. 

 

To do this the part you need is Tomix 1522, also known as V70.  The "V" stands for variable length and the piece stretches from 70-90mm, and anything in between.  This means that you can actually cut the curves to any angle you desire.  Of course, this will result in unconventional connections as the ballast will not clip together at the cut.  Many people make the mistake of thinking that Tomix 1522 is just meant to be a gap filler. 

 

Let me demonstrate how to use Tomix 1522.  Let's say that you wish to create a curve of 25° of radius 354mm.  First, you must calculate the length of the chord of the custom piece, which will be 153.25mm.  Next you need to calculate the straight distance, which is Cos 25° x 153.25 = 138.9mm.  Multiples of 70mm are 140mm and 210mm.  Of course, you cannot get a piece that is 1.1mm long, so there are some limitations to any track plan, but with Tomix 1522 extended by just 1.1mm you will get back onto the next grid increment of 210mm.

 

But Tomix 1522 only extends to 90mm and a 70mm triangle at angle 45° has a hypotenuse of 99mm.  So how do you deal with that?  Very easy!  Just add Tomix 1099, S18.5, a straight piece of track that is 18.5mm long.  Then, combined with Tomix 1522 V70, you have a piece of track that extends from 88.7 to 108.5mm.

 

Edit: -------------------------------------------------

 

Of course, I have only calculated how to get back onto the grid perpendicular to the start angle of the curve.  Good track planning with sectional track requires that you repeat this process for the perpendicular direction, ie: X and Y.  Thus you will need two pieces of Tomix 1522, one for the X direction and one for the Y direction.  The more irregular angles you use, the more pieces of Tomix 1522 you may need, but you don't necessarily need extra for every curve.  This will depend on your track plan.  You can simply continue to make the calculations for X and Y and keep a tally of how far off-grid you are.  In the end, you will need at least one Tomix 1522 in each direction X and Y somewhere on your layout to bring you back to your starting point on grid.

Edited August 3, 2014 by E6系

[miyakoji]

Everyone, many thanks for the help, I'll be referring to this thread for quite a while m(_ _)m :)