Does Size matter? (Treb. Questions)

galenow · Post by **galenow** » Sat Apr 03, 2004 7:37 pm

What are the sizes of SCA "War" Trebuchets seen at various events? How do they handle?
We are finishing up a 9' high, 12' long and 6' wide, (not including the support braces) and a throwing arm of about 10',5". and short arm and bucket 8'. It is constructed from 4x4"x12' . I figure this is probably small for what is to be found with SCA seige engines- but we could not really build it any bigger due to our school budget limits and space in our metal shop here at school. It should throw up to 10lbs pretty far with a 200lbs counterweight in the bucket according to our school computer model. It is also break-downable, and can transport in parts on a larger size trailer and truck as it is weighing in about 300 lbs assembled. I will try to post pictures as I have to present it to our school PTO, as they sponsored its construction, in about 10 days at the monthly meeting. They are coming out to the pratice football field to watch it go.

Any tips on the care and feeding of this beast (Called "Raven"-school mascot) by anyone with experience in these matters would be welcomed as we are currently sewing the sling together and placing the various ropes to fire it next week.
cheers,
galenow

Gaston de Vieuxchamps · Sat Apr 03, 2004 9:46 pm

First off, that's way bigger than most SCA trebuchets used for combat. I think I've only seem one that was a lot larger and one other that was slightly larger.

One thing, from your description it sounds like the ratio between the length between the sling and the pivot is not long enough compared to the length between the pivot and the weight. I might not have read your description right, but that's how it seemed. That ratio is very important and it might need to be toyed with a bit.

If all the ratios are right and the hook that releases the sling is right, then your treb should be able to make 10lbs really sing.

Good luck. Throwing heavy things far is cool!

galenow · Post by **galenow** » Sun Apr 04, 2004 11:48 am

Hi Gaston,
Thanks for the tip, The ratios are this: long arm 10',6" short arm and bucket together 8' adjustable to 9', with an adjustable sling 9-10' depending on the weight of the object thrown. , height is 8'6" adjustable to 9'. I'm not really sure if I got it right and field testing this week will tell.

The computer simulations say it should work with about a 70-73% eff.ratio. that is the best we could up with this size of beast. Another great thing is with canvas sheeting it also makes a splendid tent frame! We have had a lot of rain the past two days here. :shock:

cheers,
galenow

Gaston de Vieuxchamps · Sun Apr 04, 2004 11:40 pm

I'm not sure what you mean by "short are and bucket together 8'. What is the distance between the pivot point on the frame and the pivot point where the short arm is attached to the hanging bucket of counterweight.

If your throwing arm is 10'6", then your short arm should probably be less than 3'. The acceleration of gravity is constant as long as your counterweight is enough to overcome the weight of the throwing arm and the projetile. 28.8 feet per second per second? Sounds right. Anyway, making the other arm longer multiplies that acceleration and lets you get good distance.

My friend's small trebuchet gets the best distance with a 1 to 7 ratio. The only way a lesser ratio is better is if your counterweight is not heavy enough or if your arm is too heavy.

Then again, you might not want max range, you might just want "Hey cool, it works!" Either way, have fun.

I always wanted to find some old cinderblock building in the country somewhere that someone would let us destroy with a treb. I see them on the side of the road sometimes falling appart when driving to an event or somesuch and think "Hmmmm."

I've thought about making a big one sometime but then I would have to hit stuff with it :-)