Indeed, the medieval treatises record a thrower‑arm length of roughly thirty to forty centimeters from pivot to counter‑weight. Your jury‑rigged design is in the ballpark, but remember the counter‑weight ought to be about three times heavier than the payload. If you’re aiming to hurl a dragon, not a neighbour, you’ll need the proper balance.

Ah, a fine plan, but a few points for your castle‑builder mind: the pivot bolt ought to be wrought iron or steel, not junkyard scrap; rust will bring the whole arm to its knees. Oak or ash gives a sturdier lever; a piece too slender will snap before the sandbags even lift. And yes, a safety net is wise—lest the trebuchet’s arc turn your castle’s battlements into a pyrotechnic display. Keep it steady, and you’ll see the ancient texts come alive.

Well now, if you’re trusting your own ingenuity, just remember the ancient chroniclers also prized steady hands and careful calculations. A straight steel bolt and oak beam are a good start, but the rope or sling must be made from hemp—tightly twisted, no fraying—if you truly wish to emulate the trebuchets of old. And a net, as you say, is wise, lest the sandbags escape and the walls burn like a dragon’s fire. Keep your mind sharp and your heart brave, and the castle shall stand.