I am not a historian but I don't think there are any surviving medieval designs showing how you actually build a trebuchet. There are diagrams and descriptions on record, but most of them date 600+ years after the first medieval ones were used, and I'm not sure how accurate / authentic they are. They may portray what later people thought a Trebuchet should look like, rather than what they actually did look like.
Historical narratives from the middle ages state that a Trebuchet had a counterweight and used a sling, but that's about it. It is however clear that they were cutting edge technology when they were first invented, and I read somewhere that very specialist engineers were needed to assemble them, whereas any military carpenter could knock up a catapult. These early engineers had to be "booked" in advance and hired out their services to different kings at different times, until such time as the technology became more widely known, at which point armies started building their own.
I also remember reading that Edward II refused to accept the surrender of Sterling castle, because he had just built a new trebuchet to help win the siege, and having gone to all that effort and cost, he wanted to see his new Trebuchet in action. Sounds the sort of nuts thing a medieval king would do.
There was a one off TV documentary a few years ago about a team of guys who set about building a full size one for real. The team included historians, engineers, carpenters, etc, and they made a "best guess" at what they thought a Trebuchet should look like.
The first few versions they built didn't work at all, or tore themselves to bits when fired, but eventually they put together a "Civ" type Trebuchet, and it really did the business. It was amazingly accurate, and had a hell of a long range, (certainly better than the early cannons).
That said, the rate of fire on the one they built was rubbish, because they had problems with the counterweight, but it worked well enough to hint at how destructive the real Medieval ones must have been.
There's no doubt that Trebuchets were castle killers, but they were huge machines that had to be built or assembled on the spot, requiring very specialist skills, and although widely used in siege warfare, they were not as commonplace as the humble cannon. Cannons were obviously far more mobile, didn't need to be built / assembled on the spot, and like all gunpowder weapons could be used by noob troops with a minimum amount of training, (assuming said troops had some basic understanding of trajectory).
Theoretically the Castle age should really have ended the minute the first Trebuchet was fired in anger, but as we all know it was the cannon that finally did for the castle. I wonder why medieval Kings didn't make wider use of the Trebuchet? The machine could and did kill castles, but there must have been a reason why the armies of the day didn't send 20+ of the things into battle at the same time. Perhaps it was quicker and cheaper for them to expend thousands of peasants to scale the walls / mine the walls, etc.
Unusual really, because new military technology as powerful as the Trebuchet should have been quickly adopted in a completely over the top fashion by all Medieaval armies and yet they seem to have been used quite sparingly.
Does anyone know why the Trebuchet wasn't more widely used?
Regards - Mr P