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Young Jr High Disigning Bridges Obelisk

The opening of the obelisk was the climax of our story. The explorers had found all the hidden millennium pieces and solved the puzzle. When the Rod was inserted into a container the Obelisk opened to reveal a treasure.

There are simple sketches of the designs at the bottom of this page. We built the 4 sides of the obelisk with hinges on the bottom so that the sides could fold down. We then constructed a series of push bars that we hooked bungee cords to that would pull down and out on the sides to make them come down. We put a pulley onto the side of the motor and ran ropes through a series of eye bolts and connected them to the top of they pyramid walls. We would reverse the leads on the motor and the motor would slowly draw up the sides of the obelisk. While the sides were raising up we had to make sure that at our bungee cords were in place and putting pressure on the push bars on the sides of the obelisk. For the performance we would reverse the battery leads so that when the motor was switched on the ropes would unwind and the bungee cords would push down the sides of the obelisk.

The motor we used was a 24V motor taken from a construction demolition site. It operated an automatic door. We made the pulley on the shaft of the motor from wood and a large piece of PVC Pipe. We drilled holes in the PVC pipe pulley for each of the 4 ropes that ran to the sides of the obelisk so that we could feed them through the holes and adjust each rope individually.

The switch to operate the motor was a doorbell pushbutton screwed to a piece of wood in the bottom of the jar (the top of a 5 gallon water jug). We built a small open top frame box around the doorbell with sides that were just shorter than the height of the door bell button. We then loosely screwed a piece of hardboard on top of the frame surrounding the door bell. This gave us a solid surface for the rod to push on to close the door bell button.

We learned a lesson between regional and state. One day while practicing we forgot to switch the leads on the motor after raising the sides of the obelisk. When we turned on the motor it continued to roll up the ropes. The switch also stuck with the motor on. The motor was very strong and crushed several of the sides of the obelisk before we could get it turned off.

These sketches are not to scale. Only one wall of the Obelisk is shown for clarity.