Frogs

[Anonymous]

This is going to be a newbish question, but let's face it: I am a newb, even though my name claims otherwise.

What is a frog, and why does it matter whether it is insulated or not?

[dehusman]

If you look at a switch there is a place where the two rails cross each other (the right hand rail of the route going to the left crosses the left hand rail of the route going right). The place where the rails cross is called a "frog." Reasons unknown.

Since the model trains run on electric current there is positive side and negative side (two wires from the power pack). Where the two rails cross at the frog there are a couple problems. First since the left rail crosses the right rail that would short out the electrical circuit. Second , when a train goes through the left route the frog becomes part of the right rail and has to have the same polarity as the right rail. When the train goes through the left route the frog becomes part of the left rail so it has to have the same polarity as the left rail.

There are several ways to do this. Completely insulate the frog so the rails don't touch (solves problem 1) and leave it as a short dead section that has no polarity (solves problem 2). Atlas turnouts work this way right out of the box. But that creates a dead spot in the track which can stall some engines. (Amazingly, the Mantua Atlantic has a driver wheelbase that is the same length as a frog casting in an Atlas c83 #6 switch, so it stalls out every time.)
Another solution is to make the points and the frog all one piece and put insulated joints beyond the frog on the diverging routes. Then the points and the frog all have the same polarity as the rail the points touch. Walthers and Shinohara turnouts work this way. The risk here is that a metal wheel might touch the open point and the rail its on and short the system. The other risk is that the electrical connections between the points and rails might momentarily short out as the switch throws (Walthers and shinohara have that problem and have been called "DCC unfriendly").
The last option is to insulate the frog completely and then have some sort of electrical switch that routes the proper polarity to the frog. This involves additional cost and mechanical connections, but is the most reliable electrically.

Dave H.

[Anonymous]

The reason its called a frog, is that it sort of looks like a frog from the top. Use your imagination. Picture a frog that someone has stepped on, and its four legs are all stretched out in opposite directions.

[BR60103]

Get a horse book and look at a diagram of the bottom of a hoof. Find the part called the "frog". That should explain it.