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How to Build a Project-Sized Electric Drawbridge

Drawbridges were originally designed as a means of defense, in Medieval times. Many castles during this era were constructed with a moat or ditch to protect against invaders, with the only entry into the castle a defendable drawbridge. These often simple wooden platforms were hinged on one side and spanned the moat or ditch chasm. When danger neared, the castle inhabitants raised the drawbridge to prevent entry. Today, drawbridge technology is used to allow large ships to pass under bridges.

Things You'll Need

Bridge structure
Plywood
1 or 2 micro servos
1 or 2 servo controllers
Battery pack
Glue gun
Glue sticks
Band saw
Measuring tape
Eye protection

Instructions

- 1
  Select a design for your drawbridge. There are several types of drawbridges, which use different movement of the bridge platform to clear the chasm it spans. The Bascule drawbridge is most common and raises the platform vertically. Select either a one-platform or two-platform design, depending on your final application. If your project is a castle model, then choose a single platform. If your project is a model bridge, then you may select a two-platform design.
- 2
  Set up your bridge structure. Your bridge structure will be highly dependent on the type of final project of which your drawbridge will be a part. For single-platform drawbridges, your bridge structure will consist of two bases. The first structure is where the servo will be mounted and act as a hinge. The second structure must include a lip for the bridge platform to rest upon, when the bridge is in the down position. For a two-platform drawbridge, both bridge structures will be where the servos are mounted and acting as the two hinges. In both bridge designs, the structures where the servos are mounted must be large enough to accommodate this mounting, so the drawbridge platform can fit flush with the edge of the structure.
- 3
  Create your drawbridge platforms. Measure the distance from the edge of the first structure to the edge of the second structure. Measure the width of these two structures. For a single-platform drawbridge, cut the piece of plywood to these dimensions. For a two-platform drawbridge, divide the length measurement in half and cut two pieces of plywood to these dimensions.
- 4
  Connect your platform to the bridge structure. With the glue gun, hot glue your bridge platform to the servo arm. Mount the servo to the bridge structure so that when the controller is operated, the platform pivots freely. For a one-platform design, ensure the end of the platform that is not attached to the servo comes to rest on the lip of the second structure of the bridge. For two-platform designs, ensure the two platform ends are flush with one another, when both are in the down position.
- 5
  Connect the wiring of your drawbridge. Connect your servo to the controller, per the manufacturer's instructions. Mount the controller in the desired position. Connect the controller to the battery pack and mount the battery pack where desired.

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