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Software => Tutorials => Topic started by: disisme on March 18, 2006, 12:19:50 PM



Title: Tutorial 3 - elevations
Post by: disisme on March 18, 2006, 12:19:50 PM
The fact you are reading this means you have done the other 2 tutorials, so you have some idea on how to configure Xtrkcad and how to lay track.  I wont be making any concessions for people who dont know how to do that, or I'd be here all year.  If you dont know how to do it, go and do the otoher 2 tutorials first (or again...whatever :) )

OK, in this tutorial we are going to do elevations.  While you an do an entire lqayout plan without actually doing the elevations in the program, there are times when you really MUST know what grades your going to be pulling to make the overpass or whatever.  Theres nothing worse than having what seems like the perfect plan, then when you start to build it you find out you are way too steep to make that critical crossover.

In general, I tend to do my plans 'flat', then add elevation later.

click on this link and save the file as 'elevations1.xtc' in your xtrkcad folder, then start xtrkcad and open the file.
http://layoutparty.disisus.com/elevations1.xtc

You'll see that you have an 8' x 4' HO layout with a figure 8 track on it.

Now, where the tracks cross is going to present difficulties if you want 2 trains running on the mainline.  While a 30 degree crossover would do the job, thats gonna make you juggle throttles like a madman.  It would be much better to have one track pass over the other, now wouldnt it?

Set your zoom level to 8:1.  You'll see that the curves are all one piece of track, joined together by 2 straight sections.  We need to 'lift' the track where the 2 straight sections intersect.  How much we lift them is related to the scale you are modelling.  Since we're in HO, we need 3", rail head to rail head.  This allows for subroadbed, bridge bases, tunnel floor or whatever while still allowing the low train access.  Since the measurement is rail head to rail head, we only need to allow for ONE set of those structural elements.

OK, now, xtrkcad measures an elevation at a track end point (ie where two track sections join).  You'll notice on the plan that there is NO track joint at the intersecting point on either track.  Now, in theory we can raise the entire straight section by setting the same elevation at each end of it.  This would actually be quite good, because it actually provides some room for transitions.  A transitions is the changeover from grade to level, which can take a few inches that xtrkcad doesnt cater for.  If you go from an incline to a decline, the problem is compounded quite a bit and can make quite significant differences in your grade if you retain the same start and end points.  Since 3" is an abundance of headroom though, we will use a single point of elevation 'peak'.

This means we need an end-point where the tracks intersect.  Select the "Split a track" tool (4th button in the modify tracks group...looks like a piece of track with 2 red arrows pointing at it). Then go down to the track intersection and click it.  You'll see a track joint appear on one of the tracks....probably the top left to bottom right one, but it doesnt matter which....

OK, we have an end point to set our maximum elevation.  Right click in the main screen and select 'Elevation'.  Its down towards the bottom of the list.  Click on that track end point and you should get a red dot appear.  If the red dot appears on a different joint, keep clicking around that area till it appears on the joint we want.  Xtrkcad will actually select the end point closest to where you click, so you dont have to actually click on the intersection itself...just somewhere on the track that has the joint in it close to the end point.  Got it?  Good.

You'll have a little window open that will have several fields in it.  Theres a quite long list of radio buttons on the left and "None" should be selected at the moment.  The other little field boxes should be ghosted.

Change the radio button from "None" to "Defined".  The boxes become active.  The top box will read 0.00, and under that will be 2 lines that read 0.00" and 0.0%.  Since we have a flat track at the moment, thats absolutely correct.  Since we want a 3" elevation here, type 3.0 in the top box but DONT hit enter.  If you did, right click and select elevations again..... NEVER hit enter while that window is displayed because it takes it as 'OK' and closes the window.... painful. 

Right, highlight that end point again by clicking on the track close to the joint.  You window should read Defined, 3.000, 3.0" and 0.0%-0.0%.  All is good.

Hold on, why does it say 0.0%-0.0%?  There are now 2 measurements for that end point.....one for each piece of track going in each direction.  Why are they 0.0% in both directions?  Doesnt that mean the track is still flat?  Well, yes it does.  At this stage we've only defined the high point, with no low point.  Xtrkcad has, therefore, raised ALL the track to 3" automagically.

To establish a grade, we now need to define a low point to get the low track back to our benchtop.  Click on the end of the straight track thats going to be the low track.  Your elevations window will now change to particular end point.  The numbers will look pretty much the same, except "None" will be selected and the top box will be ghosted.  Click 'Defined' and type 0.0 in the top box, then click on the other end of that same straight piece.  Ignore what it says for now.... Click back on the end point you just changed the elevation on.  You should see "defined", 0.00, 0.0" and 2.0%-2.3% or numbers very close to this.  What this means is, the track is climbing through the curve at 2.3%, and the straight piece is at 2.0%. 

Click on the other end of that same straight piece again.  Now we'll take notice of the numbers in the box.  They should read something like "None", 0.401, 0.40", 2.0%.  Notice how theres only 1 grade percentage figure?  Thats because the grade on both sides of the end point are the same.

For those logoistical and mathematical geniuses out there...and arent we all...you'll have already realised that if this end oof the straight is almost half an inch above the benchwork, and the other end is ON the benchwork, then the track at the intersection point is NOT going to be at the benchwork height.... in fact, its going to be about 0.2" above the benchwork at a 2% grade.  We need to fix that or we're losing headroom for the low track, right?

OK, you should still have the 'non defined' end of the low track straight section selected and the elevations window open.  Lets change that end point to Defined and 0.0 in the top box.  What youo've got now is a perfectly flat straight track at benchwork height so it passes under the overpass with exactly 3" of headroom.

Click on the high point of the overpass again.  It should read Defined, 3.000, 3.0" and 2.3%-2.3%.  This means we have an incline of 2.3% each side of the end point...1 is an incline, the other is a decline.

Wow, this is all going well, but we have a bit of a problem.  Almost all of our track is elevated to some extent of another.... Theres probably only about 20" (20.169 actually...the length of out low track straight section) thats at benchwork height.  Lets get a steeper grade...... 

You still have the elevations window open, right?  Hit enter so it closes.  Select the 'split a track' tool and split the curve on the right at the point where the track is going straight up and down.  Right click and select elevations and set that new end point to defined 0.0 inches.  DONT hit enter, remember.... Click on the end of the 'high' straight section.  You should get "none", 2.563, 2.56" and 4.3%.  Oops... thats a little steep so we need to move that end point further away from the high point.

Click 'undo' until that end point you added on the curve disappears.  Select the 'split a track tool' and split the right curve in about the 2 oclock position.  Set the elevation here to Defined at 0.0, then click on the end of the high straight section again.  I get "none", 2.634, 2.63" and 3.6%...yours will probably differ slightly.  I now know that my 'low' point should be halfway between the straight up and down and where my new end point is to hit 4%.  Calculate from your own readings where your new end point should be.  We're aiming for CLOSE to 4%...lets not get too pedantic about being exact.... within 0.2% is close enough.

OK, that should give you a good idea on how to mess with elevations.  ITs a very simplikstic explanation, but you can 'manipulate' the track end points to get the desired results.  Go play with it and you'll get the hang of it pretty fast :)


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