Monday, June 16, 2008

Trebuchet: Part 06

Today I completed the counterweight bucket. As you can see, each side is made up of three slats. Each slat has a tenon on the end which goes into the mortises on the end caps. The bottom is a solid piece which has two tenons on each end. The uprights are held in place with ¼" dowels. They are braced to help lessen tension caused as it swings around. Between the uprights is a partition. With this in place, the two chambers are roughly square. Items can be put in to serve as a counterweight and be relatively jostle-free. The holes in the top of the uprights are where the box will attach to the arm.

Each half of the box should hold nine stacks of pennies, forty pennies high. This is about four and a half pounds. That is a quite a load. The model is 1/20th scale. So, if it were full scale, it would multiply by 20 in each of three dimensions. So 4.5 pounds x 20 x 20 x 20 = (pulling up the handy Windows Calculator) 36000 pounds! That's 18 tons of scaled counterweight! Not sure if we'll need that much, but it's good to know the power is available.

Here's the counterweight box with the frame completed so far. I checked the width, and the box does fit between the uprights. There's a little bit of wiggle room, but not much. When the arm goes onto the frame, I'll have to make sure it swings back and forth, but not side to side.

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