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.


Other Resources

Trebuchet Design

Cement Blocks


Sizing the Axle (Part 1)

Sizing the Axle (Part 2)


Car Throwing Trebuchet

Cool Trebuchet Pictures

The bucket