from: Floating Arm Trebuchet, the most effecient catapult! http://www.youtube.com/watch?v=-qDvMwa71Fg&feature=related

We are three guys from Sweden who made a Floating Arm Trebuchet as a school project. This is the most effecient catapult design known today. We managed to throw a 0.5 kg (1,1 lb) projektile 110 meters (361 ft), this gave us an effeicency of 41 %. Our counter weights were made out of concrete and had a mass of 40 kg (88 lb). The trebuchet is 2 meters (6,5 ft) high.

does th beam have to be 1:2 (te ratio between the lng arm and short arm?) and and the degree at first whenyou pull the counterweights up should there be a certain angle?

im telling you again to try to come up with your own design, there is no rules that say that a specific ratio needs to be 1:2. The angle between the ground and the arm is 45 degrees in loaded mode, nothing says thats the "right" angle tho, we just made it as simple as possible and it turned out really well..

Cool! I built a standard type 6 foot treb that launched 2lb rocks about 200 feet, using 230lb of counterweight. I heard that if you add wheels to a normal trebuchet, it is almost as efficient as the one you have here. Cool, have fun launching things!

Estimate the inside diameter by subtracting 1/4-inch from the outside diameter, if your pipe is standard Schedule 40 galvanized pipe. If you suspect your pipe is Schedule 80 extra strong pipe, subtract 3/8 inch. Schedule 120 double extra strong pipe is significantly heavier and if you suspect you have it, subtract 11/32 inch.

http://www.ehow.com/how_6390397_measure-diameter-galvanized-pipe.html

6"

3 1

/2"

1 1/2"

2 1/4"

4'-8

"

1 1

/2"2 1/4"

1'-10"

3'-8"

2'-1" 2'-1"

1'-3

1/2

"

1'-4"

1'-6 1/8"

1'-5

1/4

"

4'-3 1/2"

1 1/2"

2'-8

"

1 1

/2"

4.5” diameter wheels w/ ¾” steel axel.

Counter weight on 1” to 1 ¼” diameter axel. Could use galvanized pipe (1” I.D.).

Tip Detail The Release Pin is held on with the twine, as shown below. Make the turns neat and tight. I used glue in this area also, to help prevent the twine from fraying and give it all a little more strength. You may wish to put a right angle bend in the Release Pin, under the twine, to help keep it from twisting and insert it into a pre-drilled hole in the top of the Throwing Arm. The Eye Screw is placed on the bottom and as close to the tip as you can get without interfering with the twine wrap. http://medieval.mrugala.net/Armes%20de%20siege/Tennis%20Ball%20Trebuchet%20Plans/Tennis%20Ball%20Trebuchet%20Plans.htm

The throwing arm has a prong on the end to hook the sling ring. It is from a back yard gate locking hardware set - the bar that slips into the latch. The original prong had a small ball welded to the end of it, I sawed it off and filed down the end of the prong. The sling is made from a sliding pouch and one long, continuous piece of cord. The reason for this is that any time any parameter is changed (weight of object thrown, the weight of the counterweight, relocating the pivot point in the throwing arm) the length of the sling must be adjusted to ensure an optimal launch angle. Without an adjustable system, you'd need to have a lot of pieces of rope of different lengths to change the sling length. With the system shown here, a combination of a double-overhand slip knot (which is at one end of the rope) and an overhand loop that can be tied at any point, provides the ability to lengthen or shorten the total sling length as needed. The excess cord is run through a hole near the end of the throwing arm, then down to a boat cleat screwed into the throwing arm and wrapped between the cleat and the axle.

After the trebuchet throwing arm is pulled down as far is it can go in preparation for a launch, the cord in the picture with the ring on the end of it is passed over the top of the arm, then down between the two eye-bolts; a pin attached to the red and white trigger rope is passed though one eye-bolt, the ring, and then the other eye-bolt. The throwing arm is slowly allowed to rise until the cord has tension on it; after that all that needs to be done is pull the red/white trigger rope to pull the pin and the launch is under way.