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What is the minimum radius for oo gauge on a double track using ready to run loco's. Also how much space is needed to put in a return loop using the minimum radius?.
 

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QUOTE (TERRYSVR @ 12 Oct 2008, 18:58) <{POST_SNAPBACK}>What is the minimum radius for oo gauge on a double track using ready to run loco's. Also how much space is needed to put in a return loop using the minimum radius?.
Hi
The larger the radius the better. 24inch (600mm) minimum is ideal, but the Hornby/Peco Setrack second radius of 438mm to centres is considered the absolute minimum for most RTR stock.
 

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If you look at Hornby and other catalogues you will often see, particularly for locos, the minimum curve that the maker considers they can run on. With both Hornby and Peco now doing '4th Radius' curves (571.5mm, 22.5inch radius) you have a wider choice of ready-made curves to work with. If you have the room for larger radius curves made up from flexible track that's even better both for smooth running and appearance.

So a return loop should be a minimum of 438mm radius, or 876mm (17.25 inch) diameter and will then need 50mm (2 inch) each side for the track and clearance from the edge of the baseboard (so if the train derails it doesn't go crashing to the floor!) So you need a baseboard of at least 535mm/21 inch width for such a loop.

Regards,
John Webb
 

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QUOTE 438mm radius, or 876mm (17.25 inch) diameter

I think John has calculated the inches equivalent for the radius and forgotten to double it for the diameter. Allowing for 50mm each side, the number of mm required is 876 + 2 * 50 which gives 976 which is near enough one metre and thus 39" for the minimum width of base board give or take a wee bit.

David
 

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If the question is 'what is the minimum radius RTR OO stock will go round' then '2nd radius' is the answer.

If the question is 'what is the minimum radius for reliable running with RTR OO locomotives pulling full size trains' then with careful track laying I would suggest 24" radius as a bare minimum with 24" radius points.

If the question is 'what is the minimum radius for reliable running with RTR OO locomotives pulling or pushing full size trains' then with careful track laying I would suggest 30" radius as a bare minimum, with 36" radius points.

With a minimum radius of 36", and 36" or 60" radius points, reliability is very good indeed. If the layout is operated at scale speeds even a 'power cut' caused by a DCC shutdown rarely causes a derailment; and on investigation the root cause will usually be due to slight coupler misalignment.

I have done the experiments myself with Bachmann, Hornby and some older RTR stock and kit built locos and rolling stock, on Peco streamline to prove what was required to build an ultra reliable layout, and have accepted the space constraint that 36" minimum radius brings, in the interests of operational reliability.
 

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Adding a further and hopefully relevant question onto this post; if I was to put a test loop together of 00 to test locos before I converted them to EM lets say or for running in purposes , should I a) use set tracks or flexible and
what radius should I use? I was thinking of using some nice C&L 00 code 75 BH flexible so it at least looked nice!
 

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Discussion Starter · #7 ·
QUOTE (Lancashire Fusilier @ 13 Oct 2008, 02:13) <{POST_SNAPBACK}>Adding a further and hopefully relevant question onto this post; if I was to put a test loop together of 00 to test locos before I converted them to EM lets say or for running in purposes , should I a) use set tracks or flexible and
what radius should I use? I was thinking of using some nice C&L 00 code 75 BH flexible so it at least looked nice!

Thanks for all the replies they are very helpful, i'm using PECO flexi track with templates so will try and maintain 24" radius for the inside track.
 

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QUOTE (Lancashire Fusilier @ 13 Oct 2008, 01:13) <{POST_SNAPBACK}>Adding a further and hopefully relevant question onto this post; if I was to put a test loop together of 00 to test locos before I converted them to EM lets say or for running in purposes , should I a) use set tracks or flexible and
what radius should I use? I was thinking of using some nice C&L 00 code 75 BH flexible so it at least looked nice!
The limitation may be with the C&L flexible track. Ask the retailer or supplier what minimum radius they recommend with this track. For sure it would look nice with the C&L, but for test running purposes some 4th rad curves will do just as well. On the other hand, lay the C&L at 35" rad or greater, and you may well decide not to bother with EM...
 

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QUOTE (34C @ 13 Oct 2008, 16:11) <{POST_SNAPBACK}>The limitation may be with the C&L flexible track. Ask the retailer or supplier what minimum radius they recommend with this track. For sure it would look nice with the C&L, but for test running purposes some 4th rad curves will do just as well. On the other hand, lay the C&L at 35" rad or greater, and you may well decide not to bother with EM...

***The C&L is OK to about 30" without nipping the webs...

34C, I really like your overview you posted earlier a lot. It is a very good and well explained set of general planning guidelines!

The thing nobody added was how bad the look is with big locos and scale length coaches when radii are tight.

The real limit isn't the ability to take the curve well, but when do they stop looking acceptable!

Tight curves + big locos + coaches makes a model look like a trainset, no matter how good the scenery is! I'd say your analysis is at the small size limit... never less than 36" to look acceptable, with 60" a good "minimum target" for visible areas!

Otherwise, stay with short to medium goods stock and keep it a "pacific & long diesel free zone"

(Yes, I do know its not always easy to find the luxury of space
)

Kind regards

Richard
 

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QUOTE (Richard Johnson @ 13 Oct 2008, 08:54) <{POST_SNAPBACK}>..
Tight curves + big locos + coaches makes a model look like a trainset, no matter how good the scenery is! I'd say your analysis is at the small size limit... never less than 36" to look acceptable, with 60" a good "minimum target" for visible areas! ..
Quite so; the 36" radius is for concealed return loops - that they are concealed is part of the reason for wanting really high reliability - trains are regularly propelled off scene and return, during shunting and reversal. On the visible section I have a 40' radius curve, (about 186th radius) that's over half a scale mile; so I am 'entitled' to run trains at express speed there, and the big engines look right at home.
 

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QUOTE (dwb @ 12 Oct 2008, 23:03) <{POST_SNAPBACK}>I think John has calculated the inches equivalent for the radius and forgotten to double it for the diameter. Allowing for 50mm each side, the number of mm required is 876 + 2 * 50 which gives 976 which is near enough one metre and thus 39" for the minimum width of base board give or take a wee bit.

David
Oops! You are quite right, David, I did forget to double. My brain had obviously started to go to sleep before the rest of me!


Regards,
John
 

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Another good thing to know is that if you use panning software like xtrkcad it will calculate the radii as you design and highlight any below your target radius -

you can also use it to print out templates of your specific track.

Cheers

TimP
 

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QUOTE ... nobody had mentioned ....

Another thing no one had mentioned is "transition" curves. This is the practice of starting the curve at twice the "main" radius and then tightening into it. An old book I have recommends about one coach length at the large size. As I have no way of drawing curves directly on the baseboard, I did some calculations and found that for radii between 24" and 36", a 15 degree arc gave approximately one coach length. For a 36" radius curve I create two 7.5 degree segments for 72" and then four 15 degree segments at 36". These are finished off with another two 7.5 degree segments at 72". The result is that it takes about 48" to get through 90 degrees. I have yet to find out if it works...

David
 

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QUOTE (Lancashire Fusilier @ 14 Oct 2008, 05:30) <{POST_SNAPBACK}>Should I worry about transition curves for a test track do you think?
I wouldn't. My test track is deliberately slightly more challenging in all respects than the layout. That means that a loco or piece of rolling stock that is capable of running reliably on the test track should have no trouble thereafter on the layout.
 

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QUOTE (34C @ 14 Oct 2008, 07:10) <{POST_SNAPBACK}>I wouldn't. My test track is deliberately slightly more challenging in all respects than the layout. That means that a loco or piece of rolling stock that is capable of running reliably on the test track should have no trouble thereafter on the layout.

The last test track that we had in the workshop was deliberatly set up in this way, tight raduii, reverse curves, & so on, we even used points well past their "sell by" date, cannot fault the logic at all.
 

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This is a massively useful thread
Might I suggest it get stickied?
 

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I am about to start a new layout, I measured up last night the available space and have had to shorten the plan. So my questions is can i tighten up on the radius now that the locos are only going to move through max 90 degree bends now instead of 180.

Was thinking of shifting down to 2nd and 3rd radius from 4th and 3rd.
 
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