Knex Automatic Drawbridge Element

I created an instructable for Oblivion's drawbridge element since even I was having trouble following the pictures. I hope this helps you build Oblivion or just the element itself!

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Step 1: Lower Framework

This step contains the ramp the ball waits on until the bridge allows it to roll.

Step 2: The Main Motor

This step contains the 1st motor and the mother switch that interacts with the pulley systems.

Step 3: Upper Framework

This step contains the spool that controls the bridge movement.

Step 4: Secondary Motor

This step contains the second motor that pulls the mother switch upwards to raise the bridge. It will then automatically turn off. This is a complex step so take your time.
IMPORTANT NOTICE!!!! - Te motor in this step is a slow-turning motor found in the knex amusement part series " Drop And Swing" set.
Other motors may bee too fast for the mechanism.

Step 5: The Drawbridge

Basically it!

Step 6: Pulley Tires

My shortest step!

Step 7: Pulleys

This step is probably the longest in terms of how much adjusting you will have to make! Pay close attention to how the pulleys are attached.



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    6 Discussions

    Good job! I really like this element: it looks very complex, but the mechanism isn't that difficult.

    Excellent work bringing the drawbridge element to fuller life! ;-) Much more exhaustive than an in-step piece. One question, though. I remember when originally watching Oblivion that the bridge would make a short up-down at the bottom between lowering and raising, and still does here. It's fine, I just wondered what caused that motion. :-D

    2 replies

    The reason for that is when the bridge goes all the way down, the string starts to wind back up raising the bridge because motor two has a slight delay before it reverses the rotation making the bridge go down then raise back up. Just a little delay I purposefully implemented to give the ball a little more time to roll off the bridge.