Trains.com

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Can someone explain frogs?

4112 views
19 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    March 2009
  • 63 posts
Can someone explain frogs?
Posted by captwilb on Tuesday, January 23, 2024 4:13 PM

I have been an active model railroader for almost 20 years but I have never quite "gotten" how frogs works and how to think about them when designing a layout.  I am designing my second layout and want to better understand the differences in switch types as it related to frogs.  So if anyone can explain or direct me to a good resource I would very much appreciate it.  Thank you in advance, captwilb

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,221 posts
Posted by richhotrain on Tuesday, January 23, 2024 5:21 PM

In simple terms, a railroad frog is a device that helps the wheels rolling from one track to another.

https://railroadrails.com/information/what-is-railroad-frog/

Rich

Alton Junction

  • Member since
    December 2004
  • From: Bedford, MA, USA
  • 21,442 posts
Posted by MisterBeasley on Tuesday, January 23, 2024 5:49 PM

Unless you are hand laying track, the physical nature of frogs should not be a problem.  However, electrically there are things to consider.

Some turnouts have plastic frogs and require no particular consideration other than realizing that a plastic frog is dead electrically, so an engine may stall if going over one.

Other more high-end turnouts have metal frogs.  Those may be left dead, if you wish, but I have found that powering the frogs is helpful, particularly with short engines.  Powering frogs is pretty easy with modern switch machines, but the methods differ.

It takes an iron man to play with a toy iron horse. 

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,221 posts
Posted by richhotrain on Tuesday, January 23, 2024 6:18 PM

captwilb

I am designing my second layout and want to better understand the differences in switch types as it related to frogs. 

A simple turnout has one frog. So does a wye.

A slip (single or double) has two frogs. A crossing has four frogs.

Rich

Alton Junction

  • Member since
    December 2015
  • From: Shenandoah Valley
  • 9,094 posts
Posted by BigDaddy on Tuesday, January 23, 2024 8:56 PM

I think Mr B comes the closest to your mark.  If you have the luxury of having locos with keep alives, powering the frog is less important.

My Bachmann GE 45 tonner navigates most nearly all but one of my unpowered #5 Atlas turnouts.  Why that one is different I cannot tell.  As the turnout number increases so does the length of the frog, meaning if it unpowered, that maybe more of an issue.

Some things in life are impossible to learn.  Not that there aren't explanations, they just don't sink in.   Peco turnouts with the insulfrog, powerfrog and unifrog fall into that category for me.  What I think I know is you can't power the fron on insulfrogs or the cheap Atlas snap switch turnouts.

The other thing to be mentioned is that three way turnouts are known to be troublesome as her certain parts of the frog on Peco turnouts. Wiringfordcc.com shows the troublesome area here

Henry

COB Potomac & Northern

Shenandoah Valley

  • Member since
    July 2009
  • From: lavale, md
  • 4,665 posts
Posted by gregc on Wednesday, January 24, 2024 3:57 AM

captwilb
how frogs works and how to think about them when designing a layout.

want to better understand the differences in switch types as it related to frogs.

the basic types are left, right and wye.   but frog #s determine the angle of the diverging rails and lead-length of the turnout, the distance from the points to the frog.  different brand turnouts with the same frog # may vary in length depending on the length of track past the frog

the angle of the frog affects appearance but also how well locomotives with long wheel bases negotiate the switch.   turnouts with higher frog #s (6, 8) reqiure more space that smaller switches (4).  smaller # turnouts are better suited for yards and industrial spurs while larger # turnouts are better suited for mainline tracks

some turnouts (e.g. atlas snap switches) have curved diverging rails designed to replace curved sections of track, but most have straight diverging rails

there are electrical consequences when rails cross one another.  Frogs need to be isolated from the adjoining rails to avoid shorts. some frogs are insulated which affects locos with small wheel bases because they may lose power when the loco wheels are on the frog. Uninsulated frogs can be powered to match the polarity of the rail that the switch is aligned for.   

Tortoise switch machines have built-in switches to connect the frog to the correct track bus.   Frog juicers are electronic device like auto-reversers that detect a short when the frog power is not correct and quickly reverse the polarity to the frog

greg - Philadelphia & Reading / Reading

  • Member since
    July 2006
  • From: Bradford, Ontario
  • 15,718 posts
Posted by hon30critter on Wednesday, January 24, 2024 4:29 AM

captwilb
I have never quite "gotten" how frogs work and how to think about them when designing a layout.

Hi captwilb,

Here is my My 2 Cents worth. Basically there are two types of frogs: powered or unpowered. Which type you want to use depends largely on which locomotives you are running. If you have larger locomotives with lots of wheels to pick up power, then unpowered frogs will work for you (assuming all other factors like clean wheels and properly laid track are in place and your locomotives do not have keep alives installed). If you have smaller locomotives with relatively few axles, then you would be better off if you used powered frogs.

If you are going to use powered frogs, then you will need to be able to switch the polarity of the frogs so that, for example, if the adjacent rails are positive then the frog has to be positive and vice versa. Switching the frog polarity can be done manually with a toggle switch or you can use the circuits built into a Tortoise switch machine to do it automatically. 

I will not attempt to provide a full list of which turnouts can have their frogs powered and which can't.

There are other things to consider as well. For example, some turnouts are 'DCC friendly' which means that they don't require any modification to use in a DCC system (although their reliability can be enhanced by making a few changes), whereas other, usually older, turnouts may require some modifications in order to avoid shorts.

I will second the advice to read through Alan Gartner's 'Wiring for DCC' website. It is a bit dated but there is still lots of useful information in it.

https://www.wiringfordcc.com/switches.htm

Cheers!!

Dave

I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!

  • Member since
    October 2005
  • 1,045 posts
Posted by betamax on Wednesday, January 24, 2024 6:13 AM

There are basically two types of frogs: Insulated, which are electrically dead, and live frogs.

How you wire them depends on whether or not DC or DCC is being used, as there are slight differences between wiring requirements.

https://dccwiki.com/Turnout

has a lot of information on frogs, turnout types, and how to wire them for DCC.

Tags: DCC , turnout
  • Member since
    January 2009
  • From: Maryland
  • 12,897 posts
Posted by ATLANTIC CENTRAL on Wednesday, January 24, 2024 11:10 AM

I'm going to ask the question everyone else just assumed. Do you mean the mechanical and geometric properties of our models vs the prototype?

Or do you mean the electrical properties of our models?

Or all of it?

Sheldon

    

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,221 posts
Posted by richhotrain on Wednesday, January 24, 2024 11:20 AM

ATLANTIC CENTRAL

I'm going to ask the question everyone else just assumed. Do you mean the mechanical and geometric properties of our models vs the prototype?

Or do you mean the electrical properties of our models?

Or all of it?

Sheldon 

Great point, Sheldon. 

From the way in which the OP titled his post and phrased his question, I presumed that he was looking for a discussion of the properties of the prototype frog, not the electrical wiring of a model railroad frog. But, I could be wrong.

captwilb

I have never quite "gotten" how frogs works and how to think about them when designing a layout.  I am designing my second layout and want to better understand the differences in switch types as it related to frogs.  

Rich

Alton Junction

  • Member since
    September 2003
  • From: Omaha, NE
  • 10,621 posts
Posted by dehusman on Wednesday, January 24, 2024 4:38 PM

gregc
the basic types are left, right and wye. 

From a prototype standpoint, left, right and wye frogs in the vast majority of switches are all identical pieces of metal, the only difference is how the rails around them are configured.  Trolley tracks and switches with a very sharp diverging curvature might have a left and right configuration but they are very rare for most prototype railroads. 

There are different types of prototype frogs depending on their construction (bolted rigid frog, manganese insert, cast frogs), whether they have guard rails (self guarding frogs or jump frogs) or whether they have moving parts (spring frogs or moveable point/swing nose frogs).  And then there is, as Greg mentioned the different sizes of frogs, expresssed as a number, which is a measurement of the ratio of divergence between the routes.

Dave H. Painted side goes up. My website : wnbranch.com

  • Member since
    January 2019
  • 2,560 posts
Posted by John-NYBW on Thursday, January 25, 2024 3:52 PM

I haven't read all the replies so I might be repeating something others have said. The frog is simply the place where the rails of the two routes cross each other. On a right hand turnout, the right rail of the main route crosses the left rail of the diverging route. The rails are recessed to allow the wheels to pass through the crossing. 

This presents a potential problem electrically since the two rails that cross require a different polarity. One solution is to insulate the frog by either making it out of plastic or putting an insulated gap on all four ends of the frog, two on each route. If frog is going to be powered, it has to be wired in such a way to change the polarity depending on whether the turnouts is routed to the main or diverging route. That can be done by either wiring the frog to the turnout machine, such as a Tortoise, or having a mechanical switch attached to the throwbar change the polarity. Peco makes such a switch. 

If the frog is to be powered and it is not insulated from the frog rails, it is necessary to insulate the ends of both frog rails because the polarity for both rails changes depending on which way the turnout points are set. 

  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 23,330 posts
Posted by selector on Thursday, January 25, 2024 4:48 PM

I think you might be curious about frog 'geometry', and not about their function and powering/insulation. Is this so?

The frog number, if this is what confuses you,  is simply the number of units of length down the main axis of the turnout that the rolling stock moves for each single unit of diversion, or deviation, from the through route.  Accordingly, a #6 turnout moves the rolling stock from the points down the length of the turnout by 6 cm/inches/whatever for each cm/inch/whatever it moves the rolling stock toward the axis of the diverging route.  So, a #20 frog has a very low ratio of divergence while a #4 turnout has a very sharp angle of divergence, and you can see that from overhead when you look at examples of each number of frog.

[Edit- added...] I see, after posting, and reading the previous five or six posts, that Sheldon had already wondered the same thing...what really is the question.

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,221 posts
Posted by richhotrain on Thursday, January 25, 2024 5:17 PM

selector
 [Edit- added...] I see, after posting, and reading the previous five or six posts, that Sheldon had already wondered the same thing...what really is the question.
 

Yep, we are waiting and hoping to hear back from the OP.

Rich

Alton Junction

  • Member since
    December 2015
  • From: Shenandoah Valley
  • 9,094 posts
Posted by BigDaddy on Thursday, January 25, 2024 6:06 PM

The OP is not a one post wonder.  He will be back to tell us what he means.

Henry

COB Potomac & Northern

Shenandoah Valley

  • Member since
    February 2008
  • 2,354 posts
Posted by kasskaboose on Friday, January 26, 2024 3:18 PM

Merely adding to the speculation, does the OP mean a specific turnout #, type, manufacturer, etc. 

I presume turnout lengths also are different in real life.

 

  • Member since
    July 2009
  • From: lavale, md
  • 4,665 posts
Posted by gregc on Saturday, January 27, 2024 5:19 AM

kasskaboose
I presume turnout lengths also are different in real life.

the lead-length (frog distance in table below), the distance from the points to the frog depends on the frog #.

commercial model RR turnouts have a varying amount of the track beyond the frog.

greg - Philadelphia & Reading / Reading

  • Member since
    March 2009
  • 63 posts
Posted by captwilb on Sunday, January 28, 2024 7:50 AM

thank you very much to everyone that responded.  again, these forums have been a huge help for me.  thank you again!

  • Member since
    September 2004
  • From: Dearborn Station
  • 24,221 posts
Posted by richhotrain on Sunday, January 28, 2024 8:20 AM

You are welcome. Good to hear back from you.

Rich

Alton Junction

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Users Online

There are no community member online

Search the Community

ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!