Some Considerations for Building the Bascule Drawbridge

This is a bit of a catch-all post in support of a project to build my N-Scale Bascule Style Drawbridge.  The various model files are here and the instructables are here.

Dimensions

The smallest bridge is four sections with each section being 19 full scale feet or 37mm at scale.  I can also do five or six sections just as easily.  Clearance side to side is 28mm and from the road bed to the stringers is 40mm (which, with track laid, is too short for some cars).  The operating part of the bridge is 140mm long, 55mm wide, and stands 120mm high.  Below the table there is another 90mm needed for the motor assembly.

Power for the Bridge

The electronics stack needs 5v and the stepper motor needs 12v (though you can get one of the right form factor that will work with 5v).  You can also drive signal lights from a relay as part of the configuration and for my demo these were 12v.  In my demo configuration I took a single 12v supply and used a little voltage regulator to provide the 5v supply.  Decision Needed:  Provide both 5v and 12v to the bridge or just provide 12v.  If you just provide 12v there are a variety of voltage regulators that you can use.  If you want to trigger signal lights then you will need relays that can be actuated by the Arduino.

Options for Mounting the Electronics

My demo, as described above had the PCB, a relay that drove the signal lights, and a little voltage regulator all attached to a tray that was designed to hold the pcb and allow the other components to be tied down.  There was also another printed part for a control panel.  My assumption was that the tray would be secured somewhere with wire run to the bridge, the control panel, and to power.  The other option is a new one and that rendered the tray as a drawer that slides into two printed guides that would be mounted behind a cutout on the side of the frame the layout sits on.  The control panel becomes the front of this drawer.   What approach works best for your layout?

Configuration One

Configuration Two - Front and Parts

Configuration Two - Back

Stepper Motor Specifications

DC 5 or 12V 2 Phase 4 Wire 35mm Stepper Motor .  The under structure mount is designed for this specific motor (35mm deep).  The electronics would handle a lot of different motors but the mount would need rework (though the 42mm motor may fit).

Parts Needed for the PCB

• Arduino Nano V3
• Easy Driver - Gold Version - Cloned Version
• Screw Terminals - 5mm Pitch - 10x 2 connector, 3x3 connector, 1x4 connector
• Resistors for the LEDs - 4 x 30 ohm
• Headers - 3 x 2 pin

Other Parts Needed

• 4 x LEDs, 2 x RED, 2 x GREEN
• Push Button (SPST momentary) to fit 16mm Cutout
• Switch (SPST) to fit 9mm x 14mm Cutout
• Micro Switch Endstop x 2

Final Note

You may have noticed that my links take you to eBay UK.  I live there so that makes sense!  Simply take the verbiage from the search box and plug it into eBay US (or wherever you live).