2.9.2009 (Monday) – Day 19 –
“Going out on a limb”. This is more than a figure of speech that any kid who’s climbed in trees can explain. The further out you go; the more a tree’s limb bends or breaks. Either way, if you keep going you’re bound to fall.
The labyrinth game requires a surface for the marble to roll around on. With the Science City’s labyrinth game we’re designing it to support a #5 soccer ball. This ball only weighs about 1 pound so it is not very heavy, it is easy to handle and you can carry it around all day without much effort. But if you hold the ball in your hand and outstretch your arm it won’t take long before your arm begins aching.
If you imagine standing in the center of our 10′ x 12′ game platform and reach out to one of the far corners you would be stretching almost 8 feet. How much effort will it take to hold the ball up that far away? Our first problem is how do we extend our arm that far? What kind of materials can we find that will stay flat for a distance of 8 feet without sagging and letting our soccer ball fall to the floor? If we use an 8′ long wooden 2×4 it will support the soccer ball but it adds almost 13 pounds that we now have to lift along with the 1 pound soccer ball.
A Balancing Act
We are designing the labyrinth game to be supported from a single point at the center of the game platform. This requires a large surface that is self supporting across its entire surface. If it sags toward the outer edges it will cause the ball to roll away unexpectedly.
What kind of materials can we find that will provide a flat surface that doesn’t bend (much)? If we use 1/4″ steel plate it probably wouldn’t bend but if we use it for the entire surface it would weigh around 1,225 pounds. That would take some very large motors to make the game move.
We could try plywood in the 4′x8′ sheets. They weigh about 25 pounds per 1/4″ thickness but plywood that thin will sag toward the edges unless thicker sheets are used. If we tried building up a 2″ thick platform it would weigh about 750 pounds. This would be easier to move than the steel plate but it would still take larger motors than we want to use.
If while browsing the lumber yard looking for plywood you look another isle or two over you may find sheets of building insulation foam. A couple of similar products are the Owens Corning pink boards or Dow Chemical Company’s blue extruded polystyrene foam boards.When you pick up one of these boards up they are fairly stiff and very light weight. The 1/2″ insulation boards will sag toward the edges but if you try one of the 2″ thick boards it remains rigid across the boards length and width and at about 9 pounds it is much lighter than other building material options. If we could increase the thickness to 4″ the entire platform would weigh approximately 135 pounds. This could get us into motor sizes we’re more comfortable with.
We still have a problem when using the foam as our platform. It is not as durable as plywood or steel and pieces will begin breaking off. Inspiration for the game’s platform can be found in an office supply or art store when you buy foam core boards. These are sheets of cardboard laminated to both sides of a foam center. They make sturdy signs and art displays which are light weight. Cardboard is still not durable enough for our labyrinth platform but using outer skins of thin aluminum will give us a durable surface and relatively light
For more information about the Owens Corning Foamular brand check out this product information.