In Illustration 1, both throw bars are to the right,
making the train go left. You can see that the left and center frogs are
both of the red polarity. In this situation, the polarity of the right
frog is irrelevant.
In Illustration 2, throw bar #1 is to the left and
throw bar #2 is to the right, making the train go straight. You can see
that the left frog has green polarity and the right frog has red
polarity. In this situation, the polarity of the center frog is
irrelevant.
In Illustration 3, both throw bars are to the left,
making the train go right. You can see that the center and right frogs
are both of the green polarity. In this situation, the polarity of the
left frog is irrelevant.
At no time do the center and right frog have to have
different polarities. They are either of the same polarity (Illustration
3) , or one or the other is irrelevant. This is how the right and middle
frogs can be tied together to have the same polarity. So, all we have to
do is figure out how to control the frog polarities with the two throw
bars.
By using a set of Single Pole Double Throw (SPDT)
contacts on the switch motor, or a micro switch on throw bar #2 (the
bottom one), we can control the middle and right frogs. When throw bar
#2 is to the left, it will feed green polarity to those frogs so the
train can go to the right. When throw bar #2 is to the right, it will
feed red polarity to those frogs so the train can go straight or to the
left.
By putting a set of
Single Pole Double Throw (SPDT) contacts on throw bar #1 (the upper
one), we can control the left frog. When throw bar #1 is to the right,
it feeds red polarity to the left frog so the train can go to the left.
With throw bar #1 to the left it feeds green polarity to the left frog
so the train can go straight. If the train goes right, the left frog is
not used, so it is irrelevant.
