|
black cow press a free-rangin' publication |
|
Black Cow Press
Back to BCP Home
|
 Xtreme Engineering
-with Butch Halvorsen
Children get into trouble because they got too much time just sittin' around. Idle hands, devil's playground, you know. As kids growing up outside Des Moines in the forties, we was always into something constructive. I fondly remember when I was ten and my pals and I devised a way to keep corn fresh by injecting starter kernels with an elixir made by scraping the green stuff off of glow-in-the-dark wristwatches. But I'm getting side-tracked. That's for another day. Today we'll start with something a little easier: a Bascule Bridge.
A Bascule Bridge is a hinged structure used in a place where you have to accommodate two types of traffic, say a canal where cars go over a road which has to scat out the way when a boat comes along. You might have seen one before and called it a drawbridge. See diagrams:
*12 steel "I" beams at 30 feet long
*Scaffolding
Two tips here: First, it's important to get the ratio on those two cog gears right. The big one is fixed to the left pier and does not rotate. It oughtta' have twice the number of teeth as the little one in the middle which is fixed to the end of the right span. If you get this right, and your two spans (also called "leaves") of the bridge are of equal length and weight, the whole arrangement will balance nice, and it taxes the engine less. This, in turn, saves you a lot in fuel and maintenance over the life of the bridge.
Secondly, don't scrimp on that chain. Use a metal one sturdy enough to handle the combined weight of both leaves of the bridge. Two 30 foot spans could easily weigh more than 15 tons. All the mechanical force from the two sections pulls along the top of that chain. If it breaks you'll get hurt bad. Get your dad to help with this part.
Don't be intimidated. We built our first bascule behind the train station when I was in the fifth grade. My allowance didn't have room in it for the diesel fuel, and we reckoned we were stumped 'til Jimmy Pierson figured out how to render a substitute fuel from hog fat and soy beans. He went on to big things in... ahh, but I'm forgetting, you kids don't want to hear all about us old-timers. Have a good one, anyway. Enjoy your bridge. Build safe, and I'll see you next month, on "Xtreme Engineering," when we'll learn how to build and fly a real helicopter. -bcp
© Copyright 2003-2010, Black Cow Press. All Rights Reserved. |
