A working replica of a trebuchet.

I'm using the old boat weight bricks for the counterweight. These bricks aren't so common these days but really, anything heavy will do.

The instructions just show you how to build the brick structure. Obviously some string is also needed to make it work. You should be able to tell from the video what is needed. The sling should be about the length of the upper part of the arm. I'm using the cargo net that comes in many sets for the pouch, but a piece of cloth will also work.

Obviously the version I'm using in the video is coloured differently and has more decorative pieces. The instructions just show you how to make the basic frame in ugly colours. :)

The wheels in the instructions are different than the ones pictured above. Use whatever you have, or leave them out. They are not critical.
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Name Trebuchet
Designer JKBrickworks
Designed 2013
Inventory 290 parts
Theme Castle


  • 3 years, 2 months ago Timelord Level 19 MOC Designer PRO
    Hi Jason

    finished build 2 weeks ago very admired by all family and friends
  • 5 years, 1 month ago Bolbuyk Level 18 MOC Designer
    I just want a doublecheck from Jason or somebody else:
    If I listened well from your video you used 2 trainweights for a zamor sphere, so the counterweight is 200x the weight of the projectile. In the case of the die you used 12 trainweights, which brings me to 300x. It makes sense to me that for a heavier projectile the factor goes up more or less.
    So I want to use a Duplo 2x2 brick (6,75 gram) and should need a counterweight of nearly 2kg for about the same effect. It seems very heavy to me.
    According to your video you used 2,4kg as a counterweight for throwing your die, is that correct? And how do you make the trebuchet that solid so it can bear that weight?
    • 5 years, 1 month ago JKBrickworks Level 22 Designed this MOC
      You can use any ratio of counterweight to projectile weight you want. It will just affect the performance you get out of it. Your numbers are a bit off though. For the zamor spheres I'm using 4 train weights, so ~2 grams : ~200 grams = 100 times. For the die I'm using 12 train weights, so ~8 grams : ~600 grams = 75 times.
      • 5 years, 1 month ago Bolbuyk Level 18 MOC Designer
        Tnx for your answer. My gut told me I did something wrong with my calculations. So I think a counterweight about 500 grams will do the job, so that will be about 10 train weights or something else that heavy.
  • 6 years, 3 months ago Bolbuyk Level 18 MOC Designer
    Wow, it looks so simple but its great.
    20 feet is quite a distance!
    A pretty cave-troll from a LOTR-set would finish this nicely!
    • 6 years, 3 months ago theskirrid Level 30 MOC Designer ADMIN
      We need an onager too!
      • 6 years, 3 months ago JKBrickworks Level 22 Designed this MOC
        Some other siege machines would be cool. The biggest challenge with most of the torsion based ones is building a frame won't explode when it's used. :)
    • 6 years, 3 months ago JKBrickworks Level 22 Designed this MOC
      Oh, man I totally dropped the ball when I took the pics. A troll or two pushing it would have been an awesome addition!
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