Lionel post war early model #313 Bascule Bridge operation

[Willie]

I am wondering what the problem is with my bridge.When I activate the on button the bridge starts to lift,the cam on gear shaft passes past the stack of contact points thereby closing one set of points and opening another.At this point,I can release the button and the bridge continues to raise.The problem is that it doesnt stop at full lift,like others that I have seen operate.It continues to cycle to the down position,the cam touches the stack of contact points,thereby closing the one set ,and opening the other and shutting off power to the bridge.The only thing that I can think of is that the rotating cam must have one of those little pegs on both sides of the cam,as this is what activates or disactivates the points. That way,when the cam rotates 180 degrees (full lift) it would open the points and the bridge would stop. Help.

[rlplionel]

The bascule bridge on my layout operates in the same manner. I use an inline on-off switch to shut the power off when the bridge reaches full lift. Then, I reapply power when I want to lower it back down to track level. Here's a video of the bridge in action:

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Robert

http://www.robertstrains.com/

[lionelsoni]

I have wired my modern bascule bridges in a way that may be of use to someone.  An SPDT-CO toggle switch controls each bridge.  In the switch's center position the bridge does not move.  In the up position, the bridge rises but stops at its full height.  In the down position, the bridge falls but stops when horizontal.  I find this to be a very simple, intuitive way to operate the bridges.

The wiring is very simple:  The bridge motor's return is the layout common.  The bridge is otherwise powered through a single wire from the control panel.  The toggle switch supplies half-wave DC to the bridge by connecting the wire to one of two diodes in series with the transformer output voltage.  The diodes are connected in opposite directions so that the polarity of the DC voltage depends on which way the switch is thrown.  (Note that two diodes can serve multiple bridges.)

At the bridge, the motor has two diodes in series, connected in opposite directions.  Each of two limit switches, actuated at the two extreme positions, opens a shunt around the appropriate series diode when the bridge has reached the end of its travel, blocking the polarity of voltage that was moving it in that direction but still allowing voltage of the opposite polarity to get to the motor to move the bridge back in the other direction.

I don't have a postwar bridge; but I guess that it has a universal motor, with a field winding.  It could be used in the same way by connecting a bridge rectifier upstream of either the brushes or the field winding, to make it into a DC motor.

I use my bridges to cross a gap in my around-the-walls layout.  As built, they are useless for this, since they rise only 45 degrees.  It turns out that the gear-segment castings actually have over 90 degrees of teeth.  I have rotated these relative to the bridge itself so that my bridges can rise completely to a vertical position, allowing unobstructed entry to the room.

[BigAl 956]

As we used to say in the software industry, "That's not a bug, it's a feature!" According to the Lionel service manual that is how the postwar 313 operates. It completes an entire cycle of up then down when you press the button. The switches on the cams represent a NO contact that keeps the bridge motor going and a NC contact that kills the power to the track for an oncoming train.

Modern era 313's toggle when you press the button. They will go up and stay and come down when you press the button again.

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