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topic: 3491Slew or Transition where curve difference isn't that big
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posted: 19 Aug 2019 16:08

from:

richard_t
 
Nr. Spalding, South Holland - United Kingdom

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Hi

I have curve that needs to slew around a bridge span - the radius of one curve is 1800, and I'd like it to finish at 1747.44mm. I can't use a transition because the amount of change isn't big enough, and I'm constrained at both ends of the curve. 

I *think* I need a slew, and I've tried to do it, but the results are rubbish. I've closed a screen shot of the area (the control template and the marker coloured template are the two I wish to join), and a copy of the relevant bits from the box file, if anyone cares to lend me a hand...

Thanks in advance.

PS: I'll need to do the same for the next set of rails out...

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Attachment: attach_2885_3491_slew.box     114

posted: 19 Aug 2019 17:45

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Richard,

The problem with the transition isn't that the radii are too similar, the problem is that they are both on the same centres.

Is this any good? You didn't say how far round the curve you wanted to go on the right, so this is just my guess:

2_191229_460000000.png2_191229_460000000.png

2_191229_470000001.png2_191229_470000001.png

Box file below.

Manually create a transition having the required radii change over a suitable length. Add a slew that starts and ends just outside the transition zone. Peg it onto the outer curve on the right. Adjust the slew amount (CTRL+F7) until it is nicely over the bottom template at the end of the slewing zone. Put the peg on the end of the slewing zone position. Make split at peg to leave a short bit of plain curve. Cancel the slew in it. Recreate the bottom transition curve from it. Check running clearances on the right.

You could extend the template to replace the fixed curve top right if you prefer to have one long template.

Hope that's clear. Ask again if not. Here's the box file.

cheers,

Martin. 
Attachment: attach_2886_3491_richard_slew.box     121

posted: 19 Aug 2019 19:09

from:

richard_t
 
Nr. Spalding, South Holland - United Kingdom

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Brilliant Martin - that worked a treat.

posted: 19 Aug 2019 20:20

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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richard_t wrote:
Brilliant Martin - that worked a treat.
Hi Richard,

Glad it worked.

p.s. A more conventional solution without using a slew, would be to use only the 2 transitions, replacing the lower one with a new one:

2_191518_570000000.png2_191518_570000000.png

2_191509_170000000.png2_191509_170000000.png

The transition on the right reduces from 1800mm to 1750mm in a zone length of 700mm.

However, that wasn't what you asked for, and it modifies the concentric alignments at the bottom perhaps more than you wanted. Decisions, decisions...  :)

cheers,

Martin.

posted: 21 Aug 2019 10:47

from:

richard_t
 
Nr. Spalding, South Holland - United Kingdom

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Thanks Martin - I quite like the slewed one, so I might stick with that.

The curves join up a plan of Manchester Central pretty much to scale (until the curves that is), and the start of Cornbrook/Throstle Nest Junctions. I don't have enough space for all of Cornbrook, so only bits of it will be present (and I'll need to be on a permanent diet if it does ever get built to squeeze between Central and the main running lines - but that would probably do me good anyhow). 

499_210544_440000000.png499_210544_440000000.png

I have other plans for the top bit... and I'm undecided on the return curves to the left.


posted: 21 Aug 2019 20:51

from:

Phil O
 
Plymouth - United Kingdom

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Richard,

Have you seen Ron Heggs Manchester Central thread on Rmweb? There's some excellent architectural modelling in plastic, sorry I can't provide a link on my tablet, it's beyond my ability.

Phil

posted: 21 Aug 2019 23:02

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Phil, Richard,

It's here, but there are 136 pages:

 http://www.rmweb.co.uk/community/index.php?/topic/28293-manchester-central-clc-gn-warehouses-castlefield-viaducts/

Some amazing structure modelling.

Martin.

posted: 22 Aug 2019 09:15

from:

richard_t
 
Nr. Spalding, South Holland - United Kingdom

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Hi

Yes I'm aware of Ron's work - we've exchanged notes, photographs and drawings in the past, but I'm rarely on rmweb now.

I was hoping this would work, and with a bit of re-alignment, it looks like Manchester Oxford Road will fit, and I might get Deansgate in as well round the bend (well I must be!)

499_220414_580000000.png499_220414_580000000.png

That's just initial roughing out...

Richard.
Last edited on 22 Aug 2019 09:17 by richard_t
posted: 22 Aug 2019 13:04

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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Hi Richard,

Wow, that's ambitious! I've been thinking of adding a new option for the grid units -- months and years. :)
 
I quite like the slewed one, so I might stick with that.
Did you also try using a mode 2 slew instead? It lets you adjust the lie of the curve by changing the slew factor:

2_220749_590000000.png2_220749_590000000.png

Sorry no spare shortcut available for that. Slewing introduces a distortion to the curve, so its worth finding a setting that gives the smoothest result.

p.s. I noticed you are using a negative image for the background map. Did you see in 223c that you can now do that without leaving Templot, and also reduce the contrast, with some options for the base colour? The low-contrast function can be repeated to reduce the contrast further.

By mixing low-contrast and negative you should be able to get the optimum viewing to match the trackpad colour scheme and not distract from the track templates. 

The negative function can be reversed by simply repeating it, but the low-contrast function can't be reversed. Templot therefore makes a hidden backup of the picture shape so that you can delete the new one and go back to try again, if you wish:

2_220755_310000000.png2_220755_310000000.png

cheers,

Martin.

posted: 22 Aug 2019 14:47

from:

richard_t
 
Nr. Spalding, South Holland - United Kingdom

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Hi



I might have more of a fiddle at some point, I can move the slew up on the plan, as the viaducts out of Central aren't that long (and of course on the real thing, not on that much of a curve.)



Yes I'd noticed those new background image options - but I've not had a chance to use them as I'd already converted these maps a while back. Although I did use the twist option on Oxford road to set the line parallel to the wall.



I might need a decades grid option :thumb:

Last edited on 22 Aug 2019 14:48 by richard_t
posted: 22 Aug 2019 22:12

from:

Rob Manchester
 
Manchester - United Kingdom

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Hi Richard,

.....Old Trafford, Stretford, Dane Road.............Altrincham :D How much space have you got ? Plan is looking great, look forward to hearing of your progress.

Rob


posted: 23 Aug 2019 10:40

from:

richard_t
 
Nr. Spalding, South Holland - United Kingdom

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Well yes …. I've been watching too many tours of US layouts, some of which are multi-level, so....

The circle on the upper left could be a helix (min. radius 1250mm, 1 in 52 gradient with 150mm between tracks), and then on the lower level I could have Ashley/Mobberley/Knutsford/Plumley* under Cornbrook, a scenic break, and something near to Chester Northgate (which also stayed open in my world), under Central. Leaving space for a workbench under Oxford Road.

* One of the stations at least, between Northwich and junctions nearly Timperley so I could have some passing freight traffic.

The room hopefully will be 14m by 7m ignoring the porch, and the utility area for the heating. Domestically I've got it passed "planning", but we're not quite there with the local council. Hopefully it won't be a problem, as up the road they've had a music room of similar dimensions built in the past, and we've got more space than they have...



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