Trebuchet – Cement Blocks

10 11 2008

This weekend we had a strong surge and are very close to completing the Trebuchet!  A very special thanks to all of the those who helped!

In order to reach our goal of throwing a 6 lbs pumpkin the length of a football field we need to have a counterweight 100 times bigger.  So that means we need 600lbs of something.  Well, we looked around but couldn’t find anything that was dense enough, cheap enough.  Lead would be ideal, but where do we get 600 lbs of lead, and who wants to work with lead anyway?

So we went with the next best thing!  CEMENT!  According to the McGraw-Hill Encyclopedia of Science and Technology, “Volume generally assumed for the density of hardened concrete is 150 lb/ft^3 or 2400 kg/m^3.”

Since we need 600 lbs we need a volume of

600 lbs/150lbs/ft^3 = 4 ft^3

of cement.  This translates into 1.58 ft or approximately  20 inches on each side.   Our cement blocks are going to be 21.5 inches wide, and 19.5 deep, and 4 inches high.  We did this so the the cement blocks wouldn’t interfere with the throwing arm when the trebuchet arm is cocked back.   It will make sense once I get a picture up of that.  Anyway… here are the remain 3 blocks of concrete that are needed to make up the counterweight.

cement-blocks

Other Resources

Trebuchet Design

Cement Blocks

Counterweight

Sizing the Axle (Part 1)

Sizing the Axle (Part 2)

A-Frames

Car Throwing Trebuchet

Cool Trebuchet Pictures

The bucket

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Trebuchet – Counterweight

16 10 2008


I was able to test the basket last night by putting the cement block into the basket. The cement block fit perfectly. The cement block is 1/2″ shorter all around so that it will slip easily into the basket. After I had the block in the basket I was able to pick it up but not very high.

Other Resources

Trebuchet Design

Cement Blocks

Counterweight

Sizing the Axle (Part 1)

Sizing the Axle (Part 2)

A-Frames

Car Throwing Trebuchet

Cool Trebuchet Pictures

The bucket





The Next Project

13 10 2008
A Cement Block weighing about 200lbs

A Cement Block weighing about 200lbs

A Cement Block weighing about 200lbs

A Cement Block weighing about 200lbs

I’ve being a new journey with the help of some of my friends. We are going to build something really big. It’s going to need 3-4 of these 200 lbs blocks. These blocks were very easy to make. The first step was to create a mold that would be able to hold a 19.5″ x 21.5″ x 4″ cement block. I made the mold of of 2″x6″ and whatever piece of wood that I could drill to the bottom. Use wood screws to secure the wood in place.

The next step is to mix the 2 bags of cement. I’ve never mixed cement before so I’m not an expert, but according to the bag you slowly add water to the cement mix until it has a nice “plastic feel” to it. I’m not sure what that means, but I’m pretty sure I over watered the cement.

Next shovel the cement into the mold, and wait. The next day the cement will be dry enough to walk on, but it will be a couple of days before the cement is completely cured.

If you are still reading this post, then you are probably interested in why I am making cement blocks. It also has to do with the upcoming holiday’s, Halloween, and Thanksgiving. I mean that in the loosest sense of the word.

I’m going to be revealing a little bit at a time as the next month passes by. I’ll tell you what I can without ruining the surprise.

GOALS:
It will be finished by November 15th.
Keep it under $200.
Be able to _______ a pumpkin __________ far.

Other Resources

Other Resources

Trebuchet Design

Cement Blocks

Counterweight

Sizing the Axle (Part 1)

Sizing the Axle (Part 2)

A-Frames

Car Throwing Trebuchet

Cool Trebuchet Pictures

The bucket