Locomotive minimum track radius

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David_T
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Locomotive minimum track radius

Post by David_T » Mon Mar 25, 2013 11:27 pm

Does anyone know the simple formula for calculating the minimum radius for a model steam locomotive?
I saw it someplace, naturally, I can not remember where.

Harold_V
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Re: Locomotive minimum track radius

Post by Harold_V » Tue Mar 26, 2013 12:37 am

David_T wrote:Does anyone know the simple formula for calculating the minimum radius for a model steam locomotive?
I saw it someplace, naturally, I can not remember where.
Please correct me if I'm wrong, but wouldn't that be determined by the particular engine in question? It's subject to several variables, so there is no hard, fixed rule.

Having said that, I do believe that most tracks are built to what is considered a "minimum radius" (or greater). so it is known if a given engine can operate on the track, or not.

Harold
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kenrinc
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Re: Locomotive minimum track radius

Post by kenrinc » Tue Mar 26, 2013 2:13 am

This is a link that is often cited when this subject comes up: http://www.islandpondrailroad.com/radius.htm

Ken-

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Loco112
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Re: Locomotive minimum track radius

Post by Loco112 » Tue Mar 26, 2013 2:20 am

I'd like to see that applied to a typical locomotive, like a USRA Mikado.
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Bill Shields
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Re: Locomotive minimum track radius

Post by Bill Shields » Tue Mar 26, 2013 5:41 am

ok if you would like to see that applied, we need wheel base (fixed drivers), and lateral motion of each axle.

once you have those numbers, start plugging them in, see what you get.

There is no 'magic jinn' that can answer a mathematical questions without accurate input.
Too many things going on to bother listing them.

Pontiacguy1
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Re: Locomotive minimum track radius

Post by Pontiacguy1 » Wed Mar 27, 2013 2:53 pm

Also depends on whether or not any of the drive wheel sets are 'blind' or even have thin flanges instead of the standard thickness. You may be able to 'fudge it' by adding more to the lateral play for the axles to account for it.

It also depends on how far your lead and trailing trucks will swing, if it has any. I've seen locomotives that wouldn't go around certain curves before because the trailing truck would bind up and come off the track, or even the lead truck. Fixing that will go a long way to making one go through tighter curves.

Is this purely a mathematical consideration, or is there a particular raduis that you are trying to build a specific locomotive for?

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Bill Shields
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Re: Locomotive minimum track radius

Post by Bill Shields » Wed Mar 27, 2013 3:53 pm

without being too obvious -

if someone asking the question doesn't know to ignore blind drivers....

then perhaps they should think about something else to build .....giggle....
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hudson
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Re: Locomotive minimum track radius

Post by hudson » Wed Mar 27, 2013 4:20 pm

Hi,

Check the homepage of Giles Favell:
(he is building in 10 1/4 in gauge)

http://www.gilesfavell.seriouslyinterne ... 0index.htm

You have to scroll down a bit to see the graphical version of Baldry's formula.

Best regards,
hudson

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Loco112
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Re: Locomotive minimum track radius

Post by Loco112 » Thu Mar 28, 2013 3:05 pm

Heres are a few locomotives for your formulas. I know what radius two of them have trouble with, so we can check the results based or real world usage.

D&RG and later D&RGW;

K-36
Driver wheel base is driving wheel base 12' + 3"
It has aprox 1" total of lateral movement on the front axle.
the spacing from the front driver to the lead wheel is 40"
the spacing from the rear driver to the trailing truck wheel is 96"

K-37
Driver wheel base is driving wheel base 12' + 3"
It has aprox 1" total of lateral movement on the front axle.
the spacing from the front driver to the lead wheel is 40"
the spacing from the rear driver to the trailing truck wheel is 108"

K-28
Driver wheel base is driving wheel base 12' + 3"
It has aprox 1" total of lateral movement on the front axle.
the spacing from the front driver to the lead wheel is 39"
the spacing from the rear driver to the trailing truck wheel is 108"
total wheel base is 28' + 10"

K-27
Driver wheel base is driving wheel base 11' + 5"
no lateral motion devices
the spacing from the front driver to the lead wheel is 39"
the spacing from the rear driver to the trailing truck wheel is 66"
total wheel base is 24' + 6"
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FLSTEAM
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Re: Locomotive minimum track radius

Post by FLSTEAM » Thu Mar 28, 2013 3:08 pm

Can you apply this formula to my Shay? :D

John B.
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Fred_V
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Re: Locomotive minimum track radius

Post by Fred_V » Thu Mar 28, 2013 5:39 pm

FLSTEAM wrote:Can you apply this formula to my Shay? :D

John B.
Good one John but seriously I've been behind a Mitchcal Shay where the square drive shaft came out of the socket on every left hand curve.
Fred V
Pensacola, Fl.

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Bill Shields
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Re: Locomotive minimum track radius

Post by Bill Shields » Fri Mar 29, 2013 5:15 pm

Formula is for fixed frame calculations.

Pivoting truck locos, like the Shay have many other considerations - like u-joint angle limits and other 'interference' concerns - not binding front to rear driver.

HOWEVER, if you want to calculate using the formula, you do so defining the loco as as a 2 axle loco.

Use the distance between axles on any truck and calculate your minimum radius....
Too many things going on to bother listing them.

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