How to Assemble a Wig Wag Motor

Wig wag signals warn of approaching trains.

Railroad crossings once had signals that rocked a warning signal back and forth while lights blinked and buzzers sounded. These "wig wag" signals have largely disappeared, although the frames of wig wag signals can still be found, but the electromechanical controls -- the wig wag motors -- have to be rebuilt. The fundamental principle of rebuilt motors are the same as the original motors: an electromagnet pulls the swing arm to one side until it trips a switch that activates an opposing electromagnet that pulls the swing arm the other way to trip another switch and reverse the process.

Things You'll Need

• Frame with a swing arm attached.
• 2 electromagnets
• 2 SPST relays
• 2 SPDT micro switches
• Normally open SPST push button
• Normally closed SPST push button
• Battery
• Wires
• Tools for wiring

Instructions

1. Label one of the microswitches, one of the relays and one of the electromagnets “left” and label the other three of the same items “right.” This simplifies both wiring and description. The items designated “left” will be pulling the swing arm to the left and vice versa. The swing arm and the frame that houses the motor can be found at flea markets and antique stores. Usually the old motors have been removed.

2. Connect the positive terminal of the battery to the center posts of the two microswitches. Connect the normally closed contact of the left microswitch to one contact of the right relay. Connect the normally closed contact of the right microswitch to one contact of the left relay.

3. Connect the normally open contact of the left microswitch to one of the coil connections of the right relay, and connect a short wire from the last connection to the unconnected contact of the same relay. Connect the normally open contact of the right microswitch to one of the coil connections of the left relay, and connect a short wire from the last connection to the unconnected contact of the same relay. Connect the normally open push button between the positive terminal of the battery and the wire running between either relay and the electromagnet on the same side.

4. Connect the other coil connection of the left relay to one end of the left electromagnet. Connect the other coil connection of the right relay to one end of the right electromagnet. Connect the unused connection of both electromagnets to the normally closed push button, and connect the other side of this push button to the negative terminal of the battery.

Tips & Warnings

• In the off state, the positive battery connection is connected through each microswitch to an open relay contact so no current flows. There is another connection to a push button, but it is normally open so no current flows through this route. When this button is pushed, one magnet attracts the swinging arm to one side activation one microswitch, which starts a process where the two relays will alternately turn each other on and off until the power is removed. Pushing the normally closed push button breaks the cycle.

• The point of attachment of the swinging arm must be occasionally greased or it will have so much friction that the electromagnets cannot move it.

References

• AlphaRail: Signals and Signal Maintenance on the Central Oregon and Pacific Railroad
• RailroadSignals: Wig-Wag Crossing Signals
• TrainWeb: Wig Wag Motors

Resources

• BruceHarper: When Signals Were New