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"The Insensible" - a counterweight trebuchet

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Step 6: Counterweight

Picture of Counterweight
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120kg was deemed the correct counterweight to still be manageable, while maintaining awesomeness. Note: now that the weights have actually been made, I have altered my definition of 'manageable'. Still, 120kg in one weight would have been impossible so what we did is this:

Made four moulds from bricks. 20cm x 30cm x 10cm should fit about 30kg of concrete. Our thanks go out to Riviera park, for supplying the gravel. We collected the sand from the beach, and washed (with tank water of course!) the gravel and sand to remove organic matter from the gravel, and salt from the sand - both of which would compromise the integrity of the concrete.

We mixed up the concrete mix, sand and gravel, the poured each mould 1/3 full, placed chicken wire reinforcement inside, filled 2/3 full, put in another layer of chicken wire and filled to the top.

PVC pipe offcuts were used to make holes where the pins would attach the weights to the arm.

Then came the most important part - writing our names in wet concrete!
 
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